by its length gives 28in. for its breadth, and for that of the bar between the ports also. The exhaust port is double the breadth of the steam port, or '56in. The exhaust edges, E E, of the steam ports are 112in. apart, and that is also the breadth of the cavity of the slide valve, and the length of the cavity is the same as the ports, 2:48in. The "admission " edges, A A, of the steam ports are 1·68in. apart. The travel of the valve is equal to 34 times the breadth of the steam port, or 980, and its "lap" is one-fifth of that, or 196in., and when the valve is laid evenly over the ports its "faces" project 196in. beyond them, so that the total breadth of the valve is 2-072in., say 2 1-16in. The lead of the valve is one-fifth of the lap, or 039 = about 1-32in. full throw.

Fig. 3 will answer as an elevation of the link motion also, the throw of the excentrics is equal to the greatest travel of the valve, or 98in.; their centres, F and B, are, therefore, 49in. from the centre of the shaft whose diameter I have taken at 1in., the small side S of the excentrics I have made in. wide, and that added to the throw gives 1-48. for the width of the large sides L, hence the diameter of the excentrics is 3-23in., and their thickness may be made lin. I suppose I need not tell Mr. Watson that the mere diameter of the excentric has

every 4 of magnesia used; evaporate to dryness and
heat in an iron crucible with metallic sodium.
TESTING GOLD (4275.)-Dissolve in aqua regia.
If the solution has a blue or green colour, copper is
present; if there is a white residue upon adding water
it is alloyed with silver; if there is a precipitate with
a blue or green coloration, copper and silver are
present together with the gold.
ALABASTER GLASS (4254).—I am afraid "J."
would not be satisfied with his results if I were to give
him a method of glass analysis. I will do so if he
particularly wishes it; but I should advise him, if he
wishes for correct results, to place the specimens at
once into the hands of a professional analyst.
EFFECTS OF CARBONIC ACID (4599).-When car-

bonic acid is inhaled it produces spasms of the glottis,
which prevents the poison from entering the lungs. A
candle will not burn in a mixture of four volumes of air
to one of this gas, and the proportion that will not
support combustion will not support life. A candle
may burn in a mixture of carbonic acid and air, and
yet not support life. Six volumes of air to one of acid
would quickly act as a narcotic poison, for if suffici
ently diluted it passes the glottis and enters the lungs.
PICRIC ACID (4601).-Picric acid, also called car-
barotie and nitrophenisic acid as well as trinitro-
carbolic acid) in which three hydrogen atoms have
been replaced by nitroxyl; the formula is Ca H (NO2)
with fuming nitric acid and afterwards purifying the
O. It may be prepared by acting upon carbolic acid
product. If present with colouring matter, this latter
must be precipitated with sub-acetate of lead and the
acid taken up with ether. Its solutions are intensely
yellow. Its lead salt is soluble in water and explodes
in water and behaves as the above. Picrate of am-
on heating. The potassium salt is sparingly soluble
monia deflagrates only when heated, and solutions of
the acid possess a high yellow colour and an intensely

The boiler power will, therefore, best be deters by exemplifying what this amount of steam anga capable of doing. Assuming then a condensing s engine of 26 in. diameter of piston; the latter at 300 lineal feet per minute, we shall have a ra expansion of 1:4, and an average pressure passages, &c., and 3lb. per square inch for imp Vacuum) of 20-8621b. per square inch of piston

nothing whatever to do with its throw or excentricity; as the diameter may be increased or reduced without phenol, being in reality a substitution alcohol, is phenol deducting one-tenth of steam volume for making any alteration in its throw, and the size I have prescribed for it is merely what I should myself consider suitable for his engine.

The "lineal advance" of the excentrics is equal to the sum of the "lap and lead," or "235in.; this link is the same pattern as that in Fig. 3, and its length from pin to pin of excentric rods is equal to three throws, or 294in., say 3in. even; the length of the excentric rods is twelve throws, or 11in. nearly; the motion at the ends of this link is 98in., and at its middle it is 562in. or 9-16in.; the lead of the valve when in full throw is 039in., and when in mid lle gear it is 085in.

If I have not been sufficiently explicit in the foregoing description to enable Mr. Watson to construct a link motion for his "road-steamer" I shall have much pleasure in answering any further questions he may

ask.

JAMES BASKERVILLE,

Manager, City Foundry, Limerick.

UNNOTICED QUERIES, ETC. [331] SIR,-Having looked over the list of Unnoticed Queries I came across some I had not noticed, I therefore send you answers to them.

bitter taste.

FLUORINE (4625).-If "E. L. G." will turn to the analysis of bones in Simon's "Medical Chemistry," he will find every analysis is marked by the presence of fluorine, and if found in every sample surely it ought to be regarded as a normal constituent. Small quantities, even traces, ought not to be despised; nuclei, which cannot be discerned by the naked eye, determine the crystallization of supersaturated solutions.

CHLORIDE OF GOLD (4621).-If the gold is only alloyed with silver, place in a flask,cover with aqua regia, and digest at a moderate temperature on a water bath; when dissolved, filter and evaporate to dryness (well alloyed with copper, dissolve in aqua regia, neutralize washing the filter) on a water bath. If the gold is solution. The gold is precipitated as a fine powder, with carbonate of soda, and add ferrous sulphate which must be collected and re-dissolved in aqua regia and evaporated to dryness on a water bath.

NITRATE OF SILVER (4622). Take the plating solution, evaporate to dryness, mix with carbonate of soda to moderate the action, and heat in a clay crucible, gradually increasing the heat until the silver is completely reduced. Take the silver and dissolve in nitric acid, evaporate to dryness, re-dissolve in water and crystallize.

MAGNETIC QUERIES (4233, F. Peel). The total intensity of a magnet is that force which brings a needle to a position of equilibrium when disturbed. The total intensity is capable of being resolved into the horizontal and vertical intensity. The vertical intensity tends to make the needle dip under the influence of the terrestrial magnetism, and when one end of the needle is loaded, the vertical intensity of the north and south end counteract each other. The horizontal intensity tends to make the needle recover its position when displaced from equilibrium under the influence of the earth. The resultant of these two forces is the total intensity, from a knowledge of which the other values can easily be trigonometrically determined. SOUTH KENSINGTON EXAMINATION PAPERS (4640). Secular variation is that disturbance which is gradually-I shall be most happy to supply your triple subtaking place, and which takes centuries to complete; scriber, "J. B. H.," with a set of the above papers if thus, before 1663, the variation at London was to the he will write to me through you. They are not yet to east; at that year and a few years before it stood at be obtained through the publisher. the geographical meridian 0°, from then it gradually GEORGE E. DAVIS. went west till 1818, when it stood at 24° 41'; from then it began steadily to return, and is now about 20 W. As regards the magnetic curves, F. Peel can imagine those which occupy the field of a bar-magnet, making allowance for a spherical field, instead of a flat one, as is the case in most illustrations; he can also compare them with Sabine's chart of isoclinic lines.

ASSOCIATE IN ARTS DEGREE (4269).-Every candidate is required to satisfy the examiners in 1, English Grammar, including Analysis; 2, English Composition; 8, Arithmetic; 4, Geography; 5, English History. Questions are set in Faith and Religion; one portion of this section is, however, optional, if any objection is raised on conscientious grounds. The optional subjects are divided into four sections, of which the candidate will be required to satisfy the examiner in two. A, English History, Literature, Economy, and Law, with Physical, Political, and Com mercial Geography. No candidate will pass if he does not show a fair knowledge of one division. B, Latin, Greek, French, or German, at the option of the candidate; C, Mathematics, Geometry, Mechanics, and Hydrostatics; D, 1, Electricity, Magnetism, Light, and Heat; 2, Chemistry, including practical analysis; 3, Animal and Vegetable Physiology; 4, Geology and Mineralogy. No one passes who does not show a fair knowledge of one of these divisions. Candidates can also be examined in Drawing and Music. No one is admitted over eighteen years of age. CHEMICAL (4270).-Carbonate of soda mixed with finely divided charcoal may be distilled in an iron retort, the neck of which dips under paraffine. Caustic potash may be neutralized with tartaric acid, and the dry salt projected into a red-hot crucible; the black mass is mixed with a small quantity of charcoal, and treated as above in the case of sodium. In the case of sodium, Deville recommends the following mixture: -Dry carbonate of soda, 717 parts; charcoal, 175 parts; chalk, 108 parts; to be intimately mixed and calcined before placing into the retort. Magnesium may be procured by dissolving the caustic magnesia in hydrochloric acid, and adding 6 parts of salt to

EQUIVALENTS, PAINTING CISTERN, ETC.
[332] SIR,-I have not long been a subscriber to this
journal, but, by the kindness of an old subscriber, I
have for some time been a reader, and desire to say
that as such I have derived much useful information
and considerable pleasure, in return for which, it is
my intention to give answers to such questions as I am
able. It will also be my pleasure, if requisite, to ask
questions of other correspondents. (One I have
already asked, 4453, p. 502, to which I hope, if not a
complete answer, a partial one will be sent.) I will now
endeavour to answer a few queries.

(4537.)—EQUIVALENTS.-The question of "MaO Co,"
seems rather out of place. As no doubt you have in
some previous number given a full list of elements
with their equivalents it would therefore be a folly to
reinsert the list. I shall recommend "MaO Co" to
get "The New and Old Notation of Chemistry," by S.
W. Rich, price 1s., which is a list of elements, and the
more important compounds, 217 in all, with their
symbols, and equivalents according to both the old and
new notation, or any new book on chemistry.
stated whether the paint shelled off alone, or whether
(4560.)-PAINTING CISTERN. "Cistern" has not
it was forced off by a scale of the oxide of the iron,
which I suspect to be the case.
If so, "Cistern"
paint again with safety, it will not shell off. I am
engaged where most of the work done is ironwork, all
of which has to be painted. Experience has taught
that it is necessary to let the surface of the iron oxidize
first, scrape off the scale of oxide and then paint. The
paint will not again shell off. If the water in the
cistern is for drinking, it would be much better not to
paint at all, it being dangerous to have paints which
contain lead in communication with drinking-water.
(4519.)-TENDER FEET.-I would advise J. T. Hill
to bathe his feet frequently in strong salt and water if
sea water is not available.

may

(4492.)-RAISING WATER.-If time permits I will make a sketch and answer this next week. PSI.

and

(26

282

* 07854) x 20-862 x 300 82

horse-power.

= 107.5 indige 33000 cated thus arrived at is usually assumed at 0-5 for the The proportion of useful effect to in thus developed, would be 107.5 x 0.5 size of engine, so that the effective power of the boile (Some large boiler manufacturing firms of my se = 59-75 horses. quaintance would call this a 60-horse boiler.)

This (53 75 h.p.) gives per effective horse power per hour, 124 square feet of effective heating surface, 5:15lb. of coal, and 33-41b. of steam-results ah af actually attained in this case, might be considered sufficiently satisfactory. It is, doubtless, possible to

get more work out of this boiler by harder firing, and
indeed, instances are reported, where, with Lancashire
boilers of nearly same dimensions, as much as 5-75lb.
of water have been evaporated per square foot of
effective heating surface per hour-burning, however,
nearly 221b. of coal per square foot of same propor-
tioned) grate surface. Such results are not attainable
in regular practical boiler working, and cannot, there-
objects sought after.
fore, be estimated upon if economy and durability are
Indeed, the figure of 27. is
in the engine proper.
twice that of instances of practice in Cornwall; thee,
however, balanced by a greater percentage of “ daly

It would, doubtless, be a great boon-and I trust
these few imperfect remarks will lead to its realization
if various correspondents having the opportunity
steam boilers of various types, or already, perhaps, in
of experimenting upon the evaporative capacities of
possession of summaries of results-would carry out
and kindly publish them for the benefit of all, and expe-
cially of those less favoured, in "our" journal, along
with such "notes" of peculiarities of construction, &c.
as would enable a fair comparison with each other
being made. There is especially wanted a more com-
plete and wide-spread knowledge of the evaporative
capacities of a class of boilers now much in demand-
viz., semi-portables of the vertical and horizontal type
consisting of:-1. The vertical and horizontal fire-tube
(multitubular) boilers; 2. The vertical cross
tube boilers; and 3. The rertical "Field"
boilers, all with internal fire-box and grate, and
ployed now, especially those of the latter class #
powers up to 80 horses. For fair comparison, howeve
with the older and simpler type of boiler-the cylindr
cal with hemispherical ends, evaporating about 6.
of water per 1lb. of coal-as the most simple form to
start from, the use of the blast nozzle should be d-
carded, and the usual means of securing the requiste
draught-the chimney-alone employed. For the sa
reason cold feed should be used, or if used hot, d
should be duly accounted for.

On the continent it is usual to allow for se
portable "Field" boilers with normal draught bee
chimney about 20ft. high, 143 square feet of hes:z
surface, and 0.55 square feet of grate surface
effective horse power; and if this type of boiler,
repeatedly asserted, is capable of evaporating
water per foot of heating surfaces per hour, withe
tensifying the dranght beyond that naturally at
able by 20ft. of chimney; the quantity of steam the
raised, and that, too, at a pressure of 5 to 6 atmospheres
from zero should give out in a good non-condensin
formation is wanted, and I doubt not but that your
engine even a very much larger increment of pove
than one horse. It is evident, therefore, that more in-
esteemed correspondent Mr. Olrick will be both able
and willing to supply it; at all events, in respect to
sults at Oxford been (seemingly) unfavourable as regard
"Field" boilers-the more so as not only have the re
this type of boiler, but because there is also not wanting
men, both engineers and others, who utterly deprecate
tube (multitubular) boilers there is a great discrepanes
their employment. Then, again, as to rertical fire-
makers assume as little as 114 and others as much
in regard to their stated efficiency. Some English
effective horse power-in the
as 18 square feet of total heating surface per

the vertical surfaces of tubes above the water
one case claiming

Line

equally with those below; and in the other, putting the upper surfaces out of the question, as of no evaporative power whatever. For this class of boiler

ceived that the lines intersect each other at the opening
B, crossing each other and passing on to C. I ask
where is the focus ? Is it at this opening, or where
the picture falls on the screen D? Perhaps some of
your kind readers will help me, with, at the same time,
that indulgence for my ignorance, which is so necessary
E. O. S.
in answering the inquiries of others.

it is usual on the Continent to allow 174 square feet of
total heating surface per horse power (effective) with
steam at a pressure of 6 and 7 atmospheres from zero.
I think, sir-and this must be my excuse for occupy-
ing so much of your valuable space-that you will
agree with me that there is wanting some practical
data upon the evaporative capacities of surfaces, as
applied in the various forms of boilers now principally
in use; and I doubt not but that many others would,
equally with myself, be much benefited by such data TOBACCO AND SNUFF AS PREVENTIVES OF
being supplied through the medium of your estimable
journal.
E. W. A., Cologne.

Young Photo" (4621, 4622), had better precipitate his silver with hydrochloric acid, and sell it to a refiner, who will give him nitrate of silver, if he desires, in exchange for it. If he attempt to evaporate and fuse it he might blow up the neighbourhood, as fulminating silver may easily be formed in electroplating solutions. He may dissolve his gold in aquaregia (nitric acid, 1 part; hydrochloric acid, 3 parts), and evaporate to dryness on a sand-bath under a chimney, but he will do better to sell his gold and buy the chloride; nitrate of silver and chloride of gold, the former especially, being sold for the merest fraction over the intrinsic value of the

metal contained.

THE SATELLITES OF URANUS.

[335] SIR,-Allow me to express my thanks to Mr. Proctor [257] page 540-for so promptly taking up this question. I very much regret that I am not now able to quote the exact words of Mr. Lassell, my extracts from the "

CONSUMPTION.

[837] SIR,-At the recent meeting of the British Medical Association at Newcastle, a paper was presented by Dr. John Murray, on the above subject, to which I wish to call the attention of "our" readers. Dr. Richardson, some years ago, in a lecture on the effects of tobacco-smoking, pointed out that the greater number of the patients in our hospitals for diseases of the chest were non-smokers, and he accounted for this fact, if I remember rightly, by saying that the bronchial membranes of smokers were covered by a coating of mucus, which, he argued, protected those delicate tissues from the effects of our damp atmosphere. Whether this be true or not, Dr. Murray has now come forward as an exponent of the advantages of snufftaking as a preventive of catarrh; and, by a process of inductive reasoning, he arrives at a conclusion that smoking and snuff-taking are preservatives against, if not cures of, bronchitis and phthisis. He states that an habitual smoker seldom or never dies of consumption, and he further declares that he has seen the progress of consumption arrested by practising the habit of snuff-taking. The reasons given by Dr. Murray for this emphatic expression of opinion are as follows:-"By titillating the lining membrane of the nostrils, snuff acts as a powerful derivative and counter-irritant, and its use will tend to preserve the more important and susceptible pulmonary mucous membrane from evil. The sneezing which succeeds the unaccustomed application of the errhine, or agi tates even an old and seasoned nose when a new titillant is tried, and the cough which is induced when, by chance, some of the lighter particles get into the throat, may be of some avail in effecting the elimination of albumenoid matter (the precursor of tubercle) from the lungs-ere it has had time to fill the air-cells and minute bronchi, and coagulate-in like manner as sea-sickness is believed to do. The majority of medical men, when recovering from a common cold, will take a pinch, in order to speed the going guest.' hesitation in affirming that it will be better still as an If good to expedite the departure of a cold, I have no expedient in altogether preventing the catarrh."

exceedingly doubtful. It is more than probable
that cheap tobacco is extensively adulterated, and
it is quite possible that whatever evil effects are
laid at the door of the "fragrant weed," may be traced
to the action of the substances with which it is mixed
or prepared.
SAUL RYMEA.

ma's

TO" SIGMA."

I

[338] SIR,-I have been a diligent reader of "Sigpapers on the different kinds of battery, but have not been able to avail myself of the valuable information contained therein to the extent I had hoped for, from my previous ignorance of the subject. I shall feel much obliged if "Sigma" will, as opportunity offers, explain to me a few difficulties which I will state. don't know how many liquid grains there are in one pint, therefore I have not been able to make up a nitrate of soda solution, which I was anxious to do. In the nitric acid table (p. 266) the number of atoms in a pound decrease with the gravity, but in the fourth column the number of atoms appear to increase for the first three figures. In the above table aquafortis is treated as a weak nitric acid.

Does "Sigma" know anything of the article made to be used for all ordinary trade purposes as dipping aquafortis, which is composed of certain proportions of brown oil of vitriol, and nitrous acid, as they call it in the trade? It is a bright brown fuming acid, and a smaller proportion of it is used than of the oil, if I am correctly informed. Would not such an article give worse results than the acid mentioned in the table? A few words as to the selection of an instrument to take the gravity would be very acceptable. At the risk of being thought very dull, I must confess I have not been able to master as yet the table on page 340; but if "Sigma" will give the quantity of nitrate of soda and of acid, to make, say a pint of solution, and the number of fluid grains in the same, I think, with this additional help I shall succeed.

I certainly should not venture to ask so much, did I not recollect that probably there are others whose only source of information on many subjects is our much loved MECHANIC, and who, like myself, after honest effort have not reaped all the benefit those papers can afford.

HORSE POWER.

H. K.

[339] SIR,-I am much obliged to "R. D." (4581) for his kind reply to above query, and find that our views coincide in respect to sections 1 and 2 of query, i.e., that the pressures in boiler, when stated as in excess of the atmosphere, are to be assumed as wholly effective in non-condensing engines, whilst in condens

'Monthly Notices" being only the tobacco can be said to occasion, but, on the contrary, ing engines the force of the vacuum has to be added to

substance of them. I have notes to the effect that in
1851-2 the positions were as stated on p. 522 of the
ENGLISH MECHANIC; the apparent ellipse of the orbits
being as 8 to 6 (Vol. XII.).
In the papers by Mr. Dawes containing a discussion
of Lassell's and O. Struve's observations (Vol. VIII.) the
major axis of the orbits was assumed to be Pos. 10° and
I now see that Humboldt refers to "Astr. Nachr."
No. 493, for Madler's account of the ellipticity of the

190° in Nov., 1847.

planet.

It would be too much to expect Mr. Proctor to examine these papers for one inquirer only, but if he were induced to do so from his own interest I am not cer

tain that he would not be repaid. I am more certain that he would be helping an

FOCUS.

ETUDIANT.

FIC.3

FIC.2

It is believed, that in tobacco and snuff manufactories, the workmen do not suffer from any disease which the employés seem to have an immunity from typhus case, let the steam pressure in a given boiler be 601b. these pressures. Thus, for a clear understanding of the fever, consumption, and cholera. The majority of the in excess of the atmosphere (75lb. from a vacuum), the State physicians of France agree in believing that gross theoretical horse power of a non-condensing employment amongst tobacco is instrumental in pre-engine (full pressure throughout the stroke being preventing consumption, and may even restore consump-sumed) will be expressed by either of the following tives to health. As regards the effects of tobaccosmoking there is still much that requires elucidation. Does the empyreumatic oil or the nicotine affect, in any way, the health of the smokers? Tobacco is supposed to be repulsive to the uninitiated system because sickness and nausea invariably follow the pipe;" but then again so is the motion of a vessel at sea, which generally brings on vomiting. In the one case something may be said to be imbibed (or infumed) into the system; in the other there is nothing of the kind, unless we are to suppose that the fresh air is the cause of the sickness. Who, therefore, shall say that tobacco must be injurious because the system repels it at first? Many persons cannot partake of some species of shell-fish without nausea and sickness supervening, and instances are on record where such a simple repast as roast mutton invariably caused "alarming symptoms." But surely no one can say that either mutton or shell-fish is, per se, repulsive to the human stomach? One fact is generally overlooked by the opponents of tobacco in relying too confidently on the supposed antagonism of the system to smoking, as exhibited after the first pipe, viz., that novices do not understand the method of smoking, and so probably pump the smoke into their stomachs. Of course, no habitual smoker ever does that.

In regard to section 3 of query (Compound Engines), the answer of "R. D." is not quite so explicit. Although the reply is satisfactory as far as it deals with the question, it does not go to the full extent of the inquiry, i.e., does not explain how the power of an engine of the given dimensions and data is estimated. I with agree "R. D." that the ratio of expansion is as 1 : 4, and that the mean steam pressure is 361b. per square inch in excess of atmosphere, but I desire to know,-and it is this point upon which I trust to be enlightened,-upon what areas this mean pressure takes effect. Does it operate with its mean force upon both the pistons equally per unit of surface or only upon one, i.e., upon the largest?

It is acknowledged by all smokers that tobaccosmoking acts upon them as a sedative, and enables them to perform heavy mental labour without that nervous prostration which otherwise is its invariable concomitant. Many of our great mathematicians and literary men are, or were, great smokers; and I know gram 1), how can it be said that a picture is produced but few hard-working members of the press who are in that focus, inverted or upside down, seeing that the not habitual smokers. Sir Isaac Newton, Charles rays which are so converged do not intersect or cross Dickens, and Mark Lemon were all great smokers, each other, but merely meet or centre in one spot ? whilst Professor Masson, Mr. Punch, Fun, and others Practically I find, however, in order to obtain a clear too numerous to mention, are all well-known patrons I have noticed in a scientific work, that the power of and distinct picture, it is necessary that the lens or of the "weed." It is said by some anti-tobacco a compound engine is the same as a single cylinder enscreen, it matters not which, should be shifted so as to men, that smoking is an insidious poison, weaken-gine of the same dimensions as the low pressure cylinincrease the distance between the two, as in diagram 1, ing the brain and destroying the stomach of its der, and working with the same initial pressure of where C, B, A are the rays received on the screen, devotees. I ask for proofs. Take the great Teutonic steam and the same ratio of expansion. some distance beyond the focus F; it can be seen at nation, notorious for its inveterate habit of smoking. If this be so the gross theoretical horse power of once, therefore, that these lines having crossed each Are Germans weak, either in brain or body? Do engine particularized in section 3 (see also corrections other, that then, and not until then, does the picture they invariably die young? Or, rather, are they in No. 283, page 543) would be :become inverted. How can it be said, with respect to not a nation of deep thinkers? No one can say (262 x 0.7854) × (36 + 15) × 880 the eye and vision, that to see distinctly, or that a they are deficient in muscle. Of course, smoking distinct picture should fall on the retina, the focus carried to excess is a dangerous habit; but then, the should centre on it, as in diagram No. 2, B? I main- same applies to eating, and in fact, to everything else. tain that it would be indistinct, and not inverted; what What we really want to know is what sort of tobacco is is meant, therefore, by the focus falling on the retina, the best, and what kind of pipe most effectually reand how can it be reconciled with long and short sight? moves the poisonous properties which tobacco is said Again, if a screen with a small hole permit the rays to contain. There can be no harm in removing the of light reflected from some distant object, such as a nicotine, if possible; though whether it is really abcross A in diagram 3, to pass through it, it will be per-sorbed in sufficient quantity to do any harm is

cylinder forming the basis for estimate of power, would be demonstrated.

In conclusion I would further take the liberty of inquiring, What percentage of the gross theoretic power obtained on the basis of the foregoing formulas as applied to the three several classes of engines (single-cylinder condensing, single-cylinder non-condensing, and compound-condensing) may be safely assumed as effective from off their respective crank-shafts in the form and character of useful available power? Of course good construction and finish pre-supposed. A WORKING ENGINEER.

SCREW POWER.

[840] SIR,-I wish to submit to the scrutiny of the gentlemen who have recently been writing in the ENGLISH MECHANIC on the subject of screws and inclined plane, the following result, which I have arrived at theoretically, as to the most economical angle for the thread of a screw, but which might, at first sight, seem to contradict the commonly-received idea that the finer the thread of a screw the greater its mechanical power. Now, although if it were possible to to do away with the friction of a screw, there would, theoretically, be no limit to its power, yet as the friction of a screw absorbs a very large proportion of the power applied to turn it round, it becomes a question as to how many times it is necessary to turn it round to produce a certain effect, and as that number of times is dependent on and inversely proportional to the pitch of the screw, the question resolves itself into a consideration of the angle at which the thread of the screw is to be cut to produce the best result.

The simplest possible form in which we can present the screw with a view to this investigation is represented in Fig. 1, where the screw is itself fixed, and the nut with the weight attached is supposed to be moved round by a cord stretched horizontally and falling over a pulley with an experimental weight hung to it. And that is the form that an apparatus for determining this question experimentally would probably assume. Now for the matter according to theory:-Let angle

Р sin (i + )

cos (i + p)

=

W

..

P

=tan (i + )

W tan (i + ) and A C H cot i.

As the differentiation mentioned above is a long one, occupying nearly a whole side of letter-paper, and some of the steps being too long to be got into the space, even when written length wise of the sheet, it becomes desirable to adopt the simpler plan of approximation, with the help of a table of tangents, in which way of doing it it comes out thus:

First suppose 2 = 30 and p = 103

then tan i. cot (i + ) tan 30' x cot 40
= 577 x 1·19 = 686

Next suppose i = 50', then tan i 119 and cot
(i + p) = 577 which gives the same result as before,
so that the proper value of i probably lies somewhere
half-way between the two.

Therefore, lastly, let i= 45°, then

tan i. cot (i + p) = ·839 × ·839 = ·704
and this seems obviously a maximum without trying any
more values, from the consideration that, as the tan
and cot vary simultaneously, the largest possible pro-
duct of the two would certainly be a square, which
this is.

The illustration that I give above of the probable
form an experimental apparatus would assume is by
no means a practical one; in fact I can hardly imagine
a case in which it could be applied to any useful pur-
pose; but the usual manner in which the power of a
screw is applied is by the screw working through a fixed
nut, as in a letter-copying or ordinary house-press, or
else as in a smith's vice.

Fig. 3. Take for instance Fig. 3 as a type of the
ordinary application of a screw. Not considering the
rate or pitch of screw, let us take account of the fric-
tion. Now bearing in mind that the amount of friction
depends for the same material solely on the pressure,
and that all the rest of the calculation is a mere matter
of leverage, it becomes obvious that the friction on the
under side of the head of the screw-as it is exerted on
an annular plane, whose mean diameter is greater than
the mean diameter of the screw thread-takes more
power to overcome it than the friction of the screw-
thread itself does (unless, indeed, the nut fits the screw
very tight, which is considered by workmen to be per-
fection of work, but is on a par with many other absurd
ideas that workmen have), and the broader the collar
under the head the more loss through friction. Hence,
as it is inevitable that much more than half the power
applied to this arrangement, as compared with No. 1,
is utterly thrown away, it becomes desirable to reduce
the number of times that the screw has to be turned
round, or else to reduce the diameter of the screw and
its collar with a view of decreasing the distance from
the centre of the screw at which the resistance acts; and
this is done either by retaining the same diameter and
increasing the pitch of screw, or else retaining the same
pitch and reducing the diameter, which increases the
angle of thread, or else a judicious mixture of the
two. Also to reduce the friction of collar, make its
diameter as small as possible consistently with strength,
either making it press on its extremity (pointed if pos-
sible), as in a letter copying-press, or by making the
collar in the form of grooves as is sometimes done with
propeller shafts, recollecting that twenty gooves that
fit properly, not tight, have no more friction than one.
I believe that there is hardly an application of the
screw, except for bolts, in which this plan of very high
pitch would not tell advantageously, particularly for
planing machines, lathes, and screw presses; the
velocity of action being modified when necessary by the
application of wheels and pinions, as is done in a crab,
or crane, or screwing lathe; and I believe there would
be much greater economy of power from the less
number of times the screw itself would revolve, than
there would be loss through the additional gearing. Of
course to turn a high-pitched screw round once requires
more force or a longer lever than a low-pitched one, but
it requires doing so much less frequently.

A screw of 40 rises 8gin. with a circumference of
10in. or a diameter of 3in., or say the rise of the
thread is about 2 times the outside diameter of
the shaft, which appears extravagant, but I have
screws of 45 actually in use, so there is no question
about their working or sticking. I wonder whether the
same would hold good with propellers? I believe it
would with 43 ?

BICYCLE RIDING.

J. K. P.

[841] SIR,-Notwithstanding all that has been written on the experience of various riders, the fact is that the performance of the bicycle can be reduced to a simple sum in arithmetic. reaches 3ft. 6in. in diameter, but assuming such diThe driving wheel seldom mensions, and acknowledging that the driving wheel must inevitably measure the length of road passed over, it must make 560-7 revolutions to accomplish one mile. The action of the crank requires the legs of the which has to be made the smallest possible, or, which driver to make the same number of strokes for the same

Now, in raising the mass O through a distance equal to B C, the power P has to move a distance equal to A C, or the whole work done will be

Px AC W tan (i + p). H cot i

-WH tan (i + ). cot i

distance, and to cover seven miles, seven times the
number will be required, and to perform that distans
in one hour, 65 1 strokes per minute must be made a
rather more than one full stroke per second.
rate of motion is impossible to many, and very
could keep it up for any length of time. Theme
the statements of 8 or 10 miles an hour as havi
performed must be entirely fabulous, or executed a j
descent, when no action is required, for we slow,
unfortunately, how easy it is to go down hill.
The greatest fallacy of all is the propos
more than one driver upon a velocipede, fr
two nor fifty on one machine could increas de ned
lin. per hour. Two drivers do not divide sale,
they double it. The only means of giving ve
pede a commercial value is to cause the driva vel
or wheels to revolve with a velocity at leas
that of the legs of the driver.
HENRY W. R

AN ENGLISH MECHANIC MICROSCOPE
SOCIETY.

[342] SIR,-The thought has occurred to me, Ta
it not be a famous plan to have an "English Meta
Microscopical Society "? I believe there are a pa
many more amateurs in this very interesting m
than we, perhaps, suppose, all of whom
no doubt be glad of any little help that mu
afforded them by better hands if they only
where to find them; besides which a society so form
would be one of the best means of disposing of
duplicate slides. I am not sure that the plan Iz
about to propose is the best, but I think it a good om.

Let all those interested in microscopy send their name to the editor to be published on the "Micro." page. I the propose that the person whose name stands first, whom will call A. shall send list of duplicates (bearing his

I

name at top) to B.; at bottom of same sheet A. might
write any question he wishes to ask or make known
any idea of his own. In not more than two days after
receipt of same by B., he shall add another sheet,
bearing his name, list of duplicates, answer to A.'
questions, and anything else of interest, and forward
same to C., who will send it to D., and so on to last
member, who will send the whole on to A. A. sball
then take away his first sheet and add new one at end.
B. to do same, &c. This list may always be sent from
one member to another for a penny by book-post. The
best way to fasten sheets together in proper order will
be with one of the patent paper fasteners so generally
used.
A. A. F.

VARIOUS VARIETIES.

(No. 4536), will find some difficulty in obtaining an ex-
[348] SIR,-I fancy your querist, "Melting Point"
actly correct answer to his query, as the data necessary
does not, I believe, exist. Even if it had been ob
tained for one sample of paraffine melting at 109 Fahr.
and 128 Fahr., to all probability it would differ in an
other.

To all practical purposes, though, the melting points may be assumed to be about 115 Fahr., 114 Fahr., and 113° Fahr.

Mr. Young in his letter on page 568 is a sulphuric sed The acid solution of phosphate of lime referred to l solution of phosphate, and is also known as super phosphate.

With reference to the degree of Twaddell's hydro meter equal to 53° of Baume's, is, taking Franceour division, exactly 98°. If it would be of any use to him, I will, if possible, forward to him an approximate rule for converting Baume's into Twaddell's degrees.

44

I find "An Exhibitioner at the Royal College of Che mistry" states, on the authority of Professor Huxley, that "15 to 20 per cent." of carbonic acid gas breathed without producing any immediate evil effects, may be provided the quantity of oxygen is increased in a like proportion."

I do not know from whence the above was taken. certainly it may be from some such little work as his

for

as

Elementary Physiology," in Macmillan's series; but though I remember casually looking through that work. yet I do not remember any such statement. Perhaps though, your correspondent, "An Exhibitioner at th Royal College of Chemistry," will state his author As it stands it is almost too indefinite for even giving that Professor Huxley's opin fessor Huxley; for reading it literally and incre the oxygen in the same ratio or proportion as the bonic acid gas has been, we should have to imagine atmosphere containing some thousands per cent. of to an whole, and more than I can manage. oxygen, which is considerably worse than three halves If we are simply to increase the oxygen only to some 80 per cent., we can hardly be said to have so done, seeing we have increased the carbonic acid some hundredfold. Dr. Taylor, too, has found that a mixture of equal volumes of oxygen and carbonic acid produces death.

Dr. Angus Smith categorically contradicts the assertion that 4 per cent. of pure carbonic acid produces any apparent effects, and that from personal experience (Proc. Royal Com., 1864).

That possibly picric acid might be detected by the two extremely simple tests detailed by an "Associate of the Royal School of Mines," on page 578, is undeniable; but that it would be so done I should hardly care to so gravely affirm. Accordingly I think an "Associate" might have so far exercised his ingenuity as to have at least found some little more decided and certain test than those: acknowledging freely though the difficulty in so doing, due to the very small proportion of picric acid present.

The test of "Crow Trees," described on page 578,

is a very neat little reaction, founded on the production of a picramate; but in its practical value, hardly better than those of an "Associate of the Royal School of Mines," for the very infinitesimal amount of picric acid present in beer, and the very complex constitution of that liquid, would render it hardly more trustworthy than as an indication that picric acid might be present.

With all due courtesy I should commend to your energetic correspondent, Mr. Boord, a little care in reading queries; as of course I can but ascribe to his having very carelessly indeed read a "Young Photo's" query his very incorrect and misleading answer, that might easily cause much annoyance and expense to a "Young Photo." If I am unfortunately wrong in my supposition, and Mr. Boord did read the query with all care and attention, then I am sure Mr. Boord will accept my apologies, and excuse and kindly pardon my mistake. In that case he will allow me to assume the only other supposition, and ascribe his lapse into error to an imperfect acquaintance with the various reactions he writes concerning; so, doubtlessly he will excuse my setting matters right.

In his answer to "A Young Photo" (4622), he gravely directs him to precipitate with common salt the silver from his solution of cyanide of silver in cyanide of potassium. Now, as a matter of fact, chloride of sodium produces no precipitate whatever in a solution of the cyanide of silver in cyanide of potassium-a fact that has been known ever since Professor Ittner discovered the salt. If Mr. Boord will refer to any work on chemistry, as Fownes' or Professor Miller's, as he might almost have done before replying, I have some idea he will find it prominently stated that metallic chlorides produce no precipitate in solutions of eyanide of silver in alkaline cyanide. Also, Mr. Boord seems quite unaware that, as Professor Rammelsberg was first to ascertain, chloride of silver is very readily soluble in cyanide of potassium, which of itself would, in my idea, effectually prevent any precipitation. If Mr. Boord would so far oblige by referring to some little work, as Professor Fownes' "Manual," or Dr. Miller's "Elements," I am most decidedly under the impression that he will find the same stated therein, and which, had he but thought fit to take the trouble to refer to, would have possibly prevented his falling into so flagrant a blunder. Lastly, if I have not already troubled him too much, will he again oblige by referring to some work, and I have some idea that he will find stated therein that chloride of silver is soluble in excess of chloride of sodium.

on the line of Barriéres. The zone between these two
circuits, known as the Faubourgs, is certainly more
densely and, in the northern half, more loftily built,
even than the central city, and more solidly and
handsomely on the whole than perhaps any town in
the world; but nearly all is private, except a few in-
ferior churches and the railway termini.
must remember the Parisians have far better refuge
from bombardment than cellars or sewers; among the
bones of their ancestors, in the quarries whence all the
noble material of their city has come, undermining its

whole southern half.

Then we

E. L. G.

[847] SIR, Two things appear to have escaped the thoughts of "Thinker." 1. That the power produced, in any form, heat or motion, by a given chemical action, has been found always proportional to the number of equivalents (or what Dalton terms "atoms ") of matter, combined or set free. Now, as the equivalent (or "atomic weight") of carbon is the lowest of any but that of hydrogen, while that of zinc is rather high, they are held to be as 6 to 32. This would imply that the oxidation of 321b. of zinc in a battery can yield no more power than the burning 6lb. of coal. But, secondly, he must have overlooked that every pound of zinc he oxidizes or combines has first had to be deoxidized or set free from combination, by an expenditure of coal, for no zine is found in a free or uncombined state, as all coal is. The native oxide, or sulphuret of zinc, has first to be decomposed by an equivalent power (yielded by the combination of something else, usually native coal and native oxygen). The zinc has to be separated from those very elements, oxygen or sulphur, one or both, to both of which "Thinker " must recombine it in his battery, its whole poweryielding value to him depending on this previous artificial separation from these elements. He is, therefore, as it were, proposing to compete with an engine by the power of the water that this very engine has pumped up for him.

E. L. G.

THE FLUTE AND FLUTE PLAYING.

REPLY TO "A CUMBERLAND MINER'S
APPEAL."

[350] SIR,-If not too late, I will give a little advice
to "Cumberland Miner" (p. 307), so that he may avoid
The whole
the distressing accidents he speaks of.
cause is in the use of the pricker, which I had imagined
quite obsolete years ago, and all the replies have given
palliatives, only they have not gone to the root of the
matter. My advice is, throw away the pricker, and use
the patent safety fuse-not the gutta-percha fuse,
which I grant you, is expensive. The patent safety
fuse is only 41d. a coil of eight yards; and if required
in damp places, use the fuse with tape wound round
the outside, called by us here tape fuse. This is 6d.
the coil, but much superior to the ordinary fuse.
have used this fuse at the slate quarries in this reigh-
bourhood for the last twenty years, and have never had
an accident in the blasting during that period. The
fuse will be found less expensive than the pricker, as
the hole left by the latter must be primed with fine
sporting powder. The pricker is only fit to be put into
a museum as a relic of the dark ages. Wishing the
"Cumberland Miner" success with this fuse, I beg to
subscribe myself,
TIMOTHY BURSTALL.

THEORETICAL.

We

It seems

[351] SIR,-I have no objection to Mr. Proctor enacting the part of scientific policeman, and checking me in statements that appear to him erroneous, if the duty is fairly and courteously executed. It is difficult to judge the motives prompting the acts of others, and I fancied there was more of the spirit of counsel defending a client right or wrong, than was consistent with a philosopher seeking natural truth. from the letter (No. 241, p. 564), that I was mistaken in this surmise, and therefore hope Mr. Proctor will pardon the suspicion. But he is also wrong if he thinks me altogether unacquainted with the writings of other men on the subject of light. I am as well aware as he can be of the discordance between my views and theirs, and will explain to him in a few words the reason of the difference. The prevailing belief is, that the powers and activities of material substances result from the action of properties they inherently possess. This is not my belief, and in dissenting from that doctrine, I think myself able to advance irrefutable proof of, its fallacy. Indeed the questions I have already propounded, both to Mr. Proctor and "F.R.A.S.," were introduced for the purpose of showing the impossibility of accounting for certain natural phenomena by the prevailing theories, although readily explicable by the theory I have framed, as also others still more recondite.

I shall not now dwell farther upon this subject, having at present little leisure to work it out, but I hope shortly to show Mr. Proctor another theory of

The consequences of Mr. Boord being, as we must assume, ignorant-no, unaware of these very simple facts, and of his not having seen fit to take the immense trouble to refer to such simple sources as might have enlightened him, is that his answer to "A Young Photo," on p. 573, is erroneous and useless ab initio. [348] SIR,-Since the begining of last month I have That Mr. Boord will regret having written a wrong been so much occupied by various matters that I have having given an erroneous reply to your correspondent, ENGLISH MECHANIC, and it is only this day, 5th Sept., answer is to be supposed, and that he will regret been entirely deprived of the pleasure of reading the the cause of the zodiacal light, which I think he will "A Young Photo," is certain. that I have seen in your number of the 5th August, two letters on the flute, one signed by Mr. T. Cridland, and the other by "Flautist," and the latter, addressed to me. I will furnish the information the above two gentlemen ask for. The instruction book that Mr. Cridland wants to know about, is by John Gunn. It is an excellent work, but it is long since out of print, it was

Perhaps I have quite mistaken what "An Associate of the Royal School of Mines" intends "A Young Photo "to obtain in his answer to query No. 4622, p. 578; but if your querist, "A Young Photo," thinks he will obtain by it pure nitrate of silver he will be sadly disappointed.

Let "Paddy" (No. 4676), boil well his precipitate

with strong caustic potash, and dissolve as much as

possible in dilute nitric acid; dilute with water, filter and precipitate with sodic chloride. Collect and wash

own was not considered in his paper.

ASTRONOMICAL MATTERS.

T. A.

[352] SIR,-I am glad to see that Mr. R. A. Proctor has given Mr. Firth a few words of advice, which I hope he will profit by. Mr. Firth ought to be well acquainted with the fact that it is almost impossible to avoid errors in printing scientific matter, and especially in cases where the writers have not had proofs. Let us hope that your correspondent will see the folly of his recent of our warmest thanks. In reply to "Young Amateur" printed scale for that instrument of Messrs. Chappell (4670), the planet Saturn is situated between Ophiucus & Co., New Bond-street.

published by the author, towards the close of the last
century, and I find that the quotation is from Sir J.
Reynolds, "Academical Discourses," A.D. 1776. "Flau-
tist" is quite right in supposing that there is an
Siccama flute. I beg to inform him that he can get a
HENRY CHAPMAN.

well the precipitate, boil with pure strong caustic pot- especial fingering for many of the upper notes on the endeavour to find fault with one who is really deserving

ash, until converted into a dense black powder. This is to be dissolved in nitric acid and evaporated to dryness in a water bath; dissolve in water and crystallize; re-dissolve, neutralize with ammonia, and re-crystallize.

Mr. Proctor, I fancy, is explaining a mere supposition and unknown circumstance. URBAN.

THE PARIS DEFENCES.

[345] SIR,-There must be an error in the statement (p. 560) that "the distance from the Boulevard to the enceinte continué averages about 1,093 yards." This may be probably the smallest interval anywhere between the Barriéres (not boulevards) and the enceinte. The Barriéres are the very irregular, approximately oval, line of roads at which the shading on p. 560 terminates; including about four times the area of ancient Paris as defined by its Boulevards. These form a far more circular, or rather decagonal circuit, tolerably traceable in the plan, except on the S.E.; nowhere, I believe, so little as two miles behind the outer glacis ; and it is remarkable that they either enclose or touch every monumental or public building of any dignity, with the sole exception of the Arc de l'Etoile, which alone stands

VINE CULTURE.

[349] SIR, I have an old and vigorous vine that covers the lower half of the back of my house, which faces the west. Last year a few branches turned the corner and ran along the northern wall of my garden, and this year there are several fine bunches of grapes

on them, while there are none on the house.

wall and to check its growth on the house by keeping
This induces me to encourage its extension along the
it topped. The young branches not having been pro-
perly attended to, have grown very irregularly, some-
times in clusters of half-a-dozen, an inch apart, and I
"would fain lay knife aboard," right and left, but that
I fear, without proper advice, to take off the wrong
shoots.

me.

The only books on the subject I can refer to deal only in generalities, and do not make the matter clear to I therefore appeal to some of your readers to help me; and as it would be difficult to explain my case without drawing, I will begin from the beginning and plant a young shoot from my own or some other vine, and ask for such instruction as will carry me on to the first crop of grapes. This will enable me to treat the old vine properly at the same time.

The wall is 10ft. high, faces due south, and is exposed to the sun from 10 till 3.

What I wish to know is

1st. Will white or black grapes be preferable ?
2nd. When should the cuttings be taken and how
much of them planted?

3rd. What kind of mould should they be put into at
first, and what kind of subsoil should they have to
strike down into?

4th. Should they be struck in pots or in the places
they are henceforth to occupy?
5th. What should be the future treatment after they
are in the ground?
IN VINO VERITAS.

and Sagittarius. If, on any fine evening, he will look towards the south-west sky, he will not fail to perceive a star shining with a very steady light, and much brighter than any others in its vicinity. The planet will not be high above the horizon.

The solar spots have recently appeared in great numbers. I was much surprised, on examining the disc two or three days ago, to find that there were enormous that one or more of these groups has now passed off the groups visible in the north hemisphere. It is probable disc, but there is no doubt that the sun's photosphere expect to see is in a very disturbed state, and we may therefore numerous large and well defined A MEMBER OF THE OBSERVING ASTRONOMICAL SOCIETY.

macula.

INDUCTION AND MEDICAL COILS. [359] SIR, Mr. Coffin [304], p. 567, is quite correct in his idea (which I have frequently stated), that for medical use the induced current of the primary wire is more valuable than the more intense shocks of the secondary, though these have also their value in some cases. The plan of construction given by me in last volume furnishes both, and carries the current of the primary into the secondary and secures a current always in one direction, a matter of great importance.

In reply to the questions. A Rhumkorff coil could be used as suggested, taking care to leave the secondary circuit open, and disconnecting the condenser and providing an additional conductor and screw from the end of the primary within the break, but it would not be a wise process as a special coil is a very simple matter. A certain amount of force would be absorbed by the secondary wire even when open, but it would be small. I think that the magnetic effect on the core would be increased by increasing the middle layers, but am not certain. At all events it is unnecessary for medical use, as quite sufficient effect can be obtained from a single cell by even layers. My own coil, made

as described, gives action with a single Smee cell, varying from such a current as might be passed to stimulate the most sensitive organ, up to one which would set a strong man screaming. SIGMA.

CHASSEPOT.

[354] SIR,-We see now and then in the papers statements regarding the supply of the rifle bearing the above name to the French. The first remarks on the subject that came under my notice were about a

REPLIES TO QUERIES.

In their answers, Correspondents are respectfully requested to mention in each instance the title and number of the query asked.

[3942.)-MAKING BUTTER.-See, under the heading of Useful Notes," page 23, present volume.-SERGIUS. [3949.] "GUAYANA," OR GUIANA.-I find I have month ago, to the effect that 50,000 of these rifles sent misconstrued what "Bernardin" said; I therefore to France in the spring of the year were so many apologize. In answer to "E. L. G.," who points out my reasons for Napoleon III. deciding to make war. From error in omitting the a, I cannot acknowledge that the neighbourhood of Finsbury was stated to be their such is an error, since greater authorities do not use it. origin. This morning too, Sept. 3rd, I see in the I must certainly say, in my opinion, that the word is long, Times, in Mr. Muntz's letter, that Count Palikao stated not short, as introducing such a letter would make it. that 40,000 had been sent from this country and more The Rev. Thomas Milner, M.A., in his "Gallery of Geocontracted for. I think I can reconcile all these state-graphy," writes it as Guiana, and Stieler's "Hand Atlas" gives Guyana, so I wrote it both ways, although I do not ments thus. A firm somewhere near Finsbury did have myself think the substitution of i instead of y correct. a contract for say 50,000 rifles for the French; and early The word, as the Rev. Thomas Milner says, "is derived this year, when the time was expired for completing from the aboriginal tribe Guayanoes-a form of Wai-ini the whole order, they had done only, say 40,000, and a small tributary of the Orinoco." There does not the French Government then told them that they might exist at the present time any republic, but I find that discontinue making more, as they thought they had such territory has merged into the Venezuelan Republic, enough. This accounts for the 40,000 delivered, and as spoken of by your correspondent "E. L. G." While more said to be contracted for. This occurred before in Brazil last year, I made enquiries respecting these the second week in March, though how much before I (Quinto) had given them to the three Powers after three dependencies, and was informed that Don Joao cannot say. It is absurd to suppose that an order for which they are named for some services, but for what 40,000 rifles came over, and was supplied out of stock my informant did not say. No one who has been residsince the declaration of war. I should think few ing in Brazil, or on the South American Continent near makers kept in stock many specimens of such a the equator, can say it is healthy for Europeans.-J. G. Beestly rifle as a chassepot. Also the rifles were [4002.]-MUSLIN.-Aquilla (my better half) informs not wholly made here. The barrels, sword bayo- me that some colours may be restored to muslins or nets, and scabbards, came from France; they cashmeres very easily by simply washing them in butterwere "actioned" here and went home again to be milk.-AQUILLUS. stocked, so that although the French may have and undoubtedly did get a superior quality of workmanship in this small number (a mere fleabite compared with the whole quantity their army carries) yet had these 40,000 been entirely instead of one-half made in London, that would have had but small influence on the exact time when Napoleon III. thought proper to

declare war.

The above agrees too with Earl Granville's statement that no rifles have been sent to France since war

was declared.

A friend of mine in the course of an interview with the Emperor on another subject, three or four years ago, was asked what he thought of the chassepot, and told H.I.M. that in his opinion the chassepot was the worst military arm in Europe except the needle gun. And I am quite of opinion that the Snider is the best, and amply good enough for any soldiers in the world. I have made breechloaders myself before now, and studied the matter a little too. J. K. P.

[4208.]-ADULTERATION.-This query of J. Moody, if consigned to the limbo of the "unnoticed," will be so for the contrary reasons to the usual ones; in fact because too important, and too continually cropping up on every side. He must remember not only Mr. Bright's eternally memorable dictum that adulteration, false weights, and measures, and so forth are a form of competition;" but (as is plainly implied) they form that particular sort of competition by which Mr. Bright's "nation" (or the two mobs that we dignify with that name) have resolved to try the experiment of living. The world is, in this century, to be enlightened on the possibility of thus living; and so grand an experiment must not be interrupted. Mankind must see it carried out a outrance. A querist put exactly J. Moody's question last year, in July, in Public Opinion, and I, happening to see it, replied to this effect, that there neither is nor ought to be any means of detecting or publishing names of such traders as he and J. Moody complain of. It would be unjust if there were, for they are not of fenders. They do but act as we force them. If there be wrong-doers, it is not they who adulterate tea by putting in what ought not to be in tea; but those who adulterate mankind and the "nation," by creating therein classes of EXTRACTS FROM CORRESPONDENCE. the shopkeeper-makers that are answerable. Perhaps I beings that ought not to be. It is not shopkeepers, but hardly make this clear, but enough for the querist to rejoin immediately that when he wrote the other day plain of it as a whole," and so we parted. He may (or on our commercial system, it was not with a view to commay not) have understood the fact, that he and each what way, I will readily explain if any one wishes to one of us must either attack and fight it as a whole (in know), or accept it as a whole,-with adulteration, short weight, cheating of the blind, and all its other features. Let none dream there can be any neutral here. He must be the system's soldier or its enemy. It is because this begins to be seen by many, I think, that we hear less and less of querists like J. Moody. They see, and silently choose their side.-E. L. G.

KEEPING VARNISH BRUSHES.-A correspondent of the Hub writes: The following method of keeping brushes may be of interest to painters. Should any dirt collect in the brush while varnishing, or the brush drop on the floor, which will happen sometimes, then clean it out well in varnish, and before putting it away in the keeper fill the brush full of varnish, and in time the dirt and dust will all settle to the bottom. By cleaning it with turpentine, which is a very volatile substance, you will draw all dust and dirt up to the tin of the brush, and when using it next time it will all work out, and in many cases spoil the job. Every brush should be well dipped in varnish before putting it back in the keeper. I have used brushes now for eight years, and never had them in turpentine.

PARIS GREEN.-A correspondent says:-"Of itself I do not think Paris green is a difficult paint to manage, but it is of a delicate shade which is easily affected by outside causes. It is a good and permanent colour, but the drawback of its changing, which is so commonly experienced, is generally due to the varnish used over it. This can be proved very easily. I have a panel before me which was painted with this green eighteen months ago and varnished, and now it is of a very dark and dirty shade. But by pumicing it until the varnish is removed I find the colour beneath it is still of the original shade almost precisely. As with several other colours, the continued beauty of Paris green depends very materially upon the paleness and purity of varnish which is used over it. Paris green needs more than ordinary care in mixing, from the same reason that its shade is so easily changed. I mix it with white lead, and grind as stiff as possible in oil and a little japan gold size. As it quickly settles it should be stirred frequently during application, and should be worked as rapidly as possible, the whole panel being laid on and not touched again, otherwise it will give a streaky appearance."

AN AMERICAN SALT-MINE.-The Patriot, of San Jose, California, gives the following account of the great mine, or rather plain, of salt which lies about eighty miles N.W. of Austin, in Nevada territory, and not far distant from the railway. The mine is thirty miles long by about twelve or thirteen miles broad, without any break or interruption. The surface presents the appearance of a frozen lake with a light sprinkling of snow over it; the first stratum of salt is from twelve to fourteen inches in thickness, beneath which is a layer of argillaceous mud of a uniform depth of two feet; and under this again is the principal layer of salt, the thickness of which has not been ascertained, although a shaft has been sunk to the depth of several yards. The salt of this main stratum is described as being hard as quartz and clear as glass; it is also stated to be remarkably pure, containing only 5 per cent. of soda. The world will not want salt for a time at any rate.

[4209.]-WATER-WHEEL.-This cannot be answered without knowing approximately the quantity of water falling per minute. "J. Royd" might see from stateMECHANIC that to yield a horse-power, the weight falling ments repeated in almost every number of the ENGLISH 5ft. must be 6,6001b. (or about 660 gallons) per minute. E. L. G.

[4232.]-UNNOTICED QUERIES ON MAGNETISM. -The horizontal intensity is that of the directive force in a common compass-needle-i.e., one balanced after being magnetized-its tendency to swing back when disturbed horizontally. Vertical intensity is that wherewith a dipping needle, or one that was balanced on a horizontal axis before being magnetized, returns to the local angle of dip, when disturbed therefrom in a vertical plane, up or down. Both are measured, or their strength at different places compared, by counting at each place the oscillations made per minute by the same needle; just as local amounts of gravity are compared by the numbers of oscillations per day of the same pendulum. The needle shows the magnetic forces to vary over the globe like gravity, but to far greater extent and very irregularly. The horizontal force vanishes at the earth's magnetic poles, the compass there having no directive power; but the vertical intensity is there a maximum, as also the dip. Secular variation is the change observed in any of these data in a century; or the term expresses merely time variation as distinguished from that of locality. Four kinds, at least, of magnetic curves exist all over the globe, and are slowly changing. 1st. Those through places of like declination (or direction of the compass relatively to the meridian), and these roughly resemble meridians. 2nd. Those of equal horizontal force. 3rd. Of equal inclination (or dip). And 4th. Of equa vertical force. And of the three latter all resemble wavy parallels of latitude.-E. L. G.

[4246.]-GLYCERINE FOR COD-LIVER OIL.-We have many better substitutes for cod-liver oil. Although patients increase in weight while taking it, they rapidly fall back if it is discontinued for only a short time. MEDICUS.

[4251.]-PAINT FOR AQUARIUM.-Common paint answers very well for the aquarium, but you must varnish when dry, with a weak solution of shellac in spirit, the painting you have done outside.-MEDICUS.

[4265.]-TRANSPARENCIES. -For these, prints a

a close thin even-surfaced paper should be selecte
Colour on the right side of the picture with mout
colours, apply strong even washes and use the tip
as sparingly as possible. As the pictures are to be se
by transmitted light, they will require deeper cole
To determine the exact depth will require practice. S
should be kept very clear. Prepare a solutio
Canada balsam (not too thick) in rectified oil of tas
tine, coat the face of the coloured picture n
evenly with this cement, taking care that no parte
left untouched by the brush, and immediately agya
the glass which must be scrupulously clean,
closely and carefully, expel all air bubbles or the
become hard and dry (about thirty hours will
will be irrecoverably spoiled. When the
this) varnish with the best picture copal. F
hair tools should be employed for the cen
varnish. The following are the proper coloan
madder, pink ditto, yellow lake, Italian pisk
umber, burnt sienna, brown pink, Prussian bia. G
shades of purple may be made with the madders
blue, also in green with the yellows and blue, and to
adding little burnt sienna as in draperies, &c., in vim
and the browns. The madders may be enric
case, shade with madder mixed with burnt amber. Te
dyke brown is a useful colour in transparent paints
Use a little ox-gall with the water in colouring, and ad
gum and dust.-SABLE.

[4288.]-FORCE-PUMP FOR IRRIGATION.-Small They are very useful for watering flower or kitche portable force-pumps are made by most pump-maken gardens. They will throw from 30 to 40ft. Price she 30s. Names of makers can be found in "The Directory and in the advertisement pages of "our" journal-SED GIUS.

[4361.]-METHYLATED SPIRIT.-I beg leave to con tradict most emphatically the statement of "T.L. H. that "as a rule all the tinctures now sold in chemists' shops are prepared with the methylated spirit, and many could be no greater mis-statement, or greater display of of such tinctures are for internal application." There ignorance on the part of "T. L. H." than this. No respectable chemist would ever dream of making tinedid so he would find them unsaleable. Moreover, the tures for internal use from methylated spirit, and if he use of methylated spirit is now strictly prohibited in the manufacture of any medicine for internal ase, except ether and chloroform. This is on account of cleaned spirit " having been sold by some unscrupulons druggist among the poorer classes as a stimulaat, under various names. Methylated spirit may be used for liniments, with the purchaser there can be no objection.-HENRY &c., for external use, and where cheapness is an object JAMES, Pharmaceutist, Woolwich.

[4383.]-THREE COINS.-Though I am no judge of coins, I fear there is a misprint in W. J. Eggleston's reply to "Hastings." Should not "London" (first word, fourth line) be "Londonderry"? "John Ervin at ye ferry of Londonderry."-AQUILLUS.

[4298.)-MILLERS.-In reply to the query of "J. S. H.," I beg to send the following description of Howes, Rabcock, & Co.'s " Eureka Smut and Separating Machine," one of which we have been using for some time, and find it far surpasses any other machines which we have hitherto tried for cleaning Ghirka or other kinds of wheat. Cut No. 1 is a perspective view, one section of

the outer easing being removed. It represents, on the right, the screenings dropping from the separator, and on the left, at the bottom of the machine, the discharging of grain. No. 2 is a sectional view, showing an internal arrangement of the machine. The direction of the arrows represents currents of air, created by the action of the fan through the separators and different parts of the machine, for separating the grain, collecting the dust and other impurities, and discharging them out of the mill. On the left showing the wheat entering