tained at as high a temperature as possible point, the proper position for the shunt is shown
without volatilising the zinc; that is to say, to at Fig. 9, where F and F' are the field magnets of
about 1,200 Fahrenheit, and the zinc will then the dynamo, S being the armature, the wires
take up as much as possible of phosphuret of from which make connection through the commu-
iron, ferro-manganese, or spiegel-eisen, about tator to the binding screws A and A'. When we are
8 or 9 per cent. in each case. If the bath is kept working our dynamo as a series machine against
at a lower temperature, the amount of phosphuret a small and unvarying resistance, we connect the
of iron, or ferro-manganese, or spiegel-eisen binding screws Aʼand B' with the outer circuit,
taken up
will be less than 8 ог 9 per in which case the current leaving the armature
cent., the amount SO taken up depending flows along to the binding screw A, which is
upon the temperature employed. As the connected with the field magnet binding screw B
proportional quantity of phosphorus or man- by the fixed piece C, and from thence in the
ganese combined with the iron will be known, direction of the arrows round the convolutions of
it is evident that the requisite quantity F, into F', round F', to B', which is one of the
of iron and phosphorus or manganese can be in-binding screws used for the main circuit. From
troduced into the alloy with great nicety and thence the current traverses the outer circuit C,
accuracy. The saturated composition is, where the work is to be performed, and then
with or without a quantity of pure zinc, added to re-enters the dynamo by the binding screw A',
molten copper. The proportions of copper and which is connected with the negative brush of
zinc employed in the manufacture of the above the commutator. But if the outer circuit pre-
alloys are from 45 to 75 per cent. of copper com- sents too great a resistance, or is variable, so
bined with from 55 to 25 per cent. of zinc that the quantity of electricity it allows to cir-
compound containing the phosphuret of iron, culate round the field magnets is insufficient or
ferro-manganese or spiegel-eisen or mixture of unequal, then a shunt is introduced at C', and
the same alone or combined with pure zinc. the outer circuit is completed by coupling up the
Ferro-manganese frequently contains silicium, binding screws A' and A, to whatever work it is
which increases the tenacity of the alloy, and if
the proportion of the silicium contained in the
ferro-manganese exceeds one half per cent., Mr.
Dick adds a proportionally larger per-centage of
pure zinc than he would do if no silicium were
present. The preliminary combination of zinc
with the phosphuret of iron, ferro manganese, or
spiegel-eisen, as effected by the method de-
scribed, requires but a comparatively low tem
perature for its formation, the phosphuret of
iron, ferro-manganese, or spiegel-eisen being
brought into contact with the molten zinc while
in the solid state (in excess) whereby the oxida-
tion of the phosphorus or manganese present is
avoided, which is not the case when the phos-
phuret of iron, ferro-manganese, or spiegel-eisen
is melted at a high temperature and then added
to the molten copper, it being well known that
the ferro-manganese and spiegel-eisen require an
extremely high temperature to melt them.

EXPERIMENTS WITH THE HAND
DYNAMO.-III.*

By S. R. BOTTONE.

UR" dynamo is eminently adapted to will work well and easily (id est, without fatiguing the operator) any coil capable of giving from in. up to 1in. spark. It will be found necessary to use a shunt in working these coils; not so much because they present resistance (though that, of course, affects the current), as because the break and make contact arrangement of the induction coil entirely cuts off the current from circulating round the field magnets at every oscillation of the clapper, unless a shunt is used; and this interruption of current, militates very strongly against the production of the best effects, since the field magnets have not time to get magnetised to the full. About a foot of No. 36 iron wire will be found to give the the proper resistance for any ordinary-sized coil. In order to get the best results, both in this and in other experiments, it is well to have at hand shunts of stated varying resistances. These are easily made of sufficient accuracy by coiling up in a helical form around a pencil, different lengths of No. 36 iron wire, which can then be inclosed in short lengths of glass tubing, the extremities of the wire passing through corks placed at each end of the tube. (Fig. 8 shows the arrangement.)

B'

Fig 8

Fig. 9

S

F'

F

B

coil, as usual for vacuum tube experiments, and having darkened the apartment in which the experiment is performed, to attach to the coil a plain vacuum tube containing a little phosphorescent powder (freshly calcined barium and calcium sulphides). On turning the handle of the dynamo the coil works, and the tube becomes illuminated with ruddy purplish streamers; on stopping the dynamo this coloured light ceases, but the phosphorescent sulphides glow with a beautiful soft light, which by contrast appears greenishwhite. Vacuum tubes containing phosphorescent powders may be obtained from the electrical warehouses; but should these not be at hand, a very fair substitute may be extemporised, by placing a small phosphorescent tablet (one of such as are sold along with lucifer boxes) against an ordinary vacuum tube, and then setting the coil in action. The phosphorescence is not, however, quite so vivid as when the powder is inside the tube.

MICROSCOPIC ITEMS.*.

tubes, &c., use a piece of the round leather NOR a good swab for cleaning small vials, test belting sold by dealers in sewing machine supplies. Disinfectants.-What is the best disinfectant? Answer-A high degree of cleanliness. There is no disinfectant besides this that is perfect in its action. If not thorough, it is almost useless. Many disinfectants only narcotise disease germs, but do not destroy them.

Method for Double Injections.-The veins are first injected through the arteries with coloured gelatine, and then a differently coloured plaster of Paris is injected in the same way, forcing the gelatine before it, but as this stops at the capillaaies, the arteries and veins can readily be distinguished.

The Beautiful Snow.-From the pure and beautiful snow, just fallen, Floegel has obtained living infusoria and algae, bacilli, and micrococci, mites, diatoms, and great numbers of fungi spores, also fibres of wood, mouse hairs, pieces of butterfly wings, skin of larvae of insects, cotton fibres, pieces of grass, epidermis, pollen grains, rye and potatoe flour, grains of quartz, minute pieces of roofing tiles, and bits of iron and coal.

A Pretty Slide-A very pretty slide, and one very easily made, is the raphides in the sap of the daffodil. It is only necessary to squeeze out a drop of sap from the flowering stem on to a slide, and on its drying, which may occur spontaneously, or be done over a spirit lamp, we find hundreds of crystals strewn over the field of view. With the polariscope they are exceedingly interesting and brilliant. If we drop over the warmed glass a little Canada balsam, we can press on a cover glass.

Simulation of the Tubercular Bacillus.-The memoirs of A. Čelli and C. Guarnieri give the results of a large number of observations on the bacillus described by Koch in the nodules of tuberculosis and in the sputa of consumptive patients, and further call attention to certain crystals found not uncommonly in these sputa, which, both by their appearance and by their behaviour toward aniline colours, imitate the tubercular bacilli. The

microscopic differences between the two classes of objects are minutely described.

desired to perform. It will be seen by the ar-
rows that the current divides itself along two
routes, one part going round ABCFF B'C'A',
Examining Alive the Heads of Insects, Spiders,
and returning into the armature, while the other&c.-Mr. E. T. Draper recommends a cone of
portion branches off at A', and passing into O pasted paper to be made rather larger than the
(the outer circuit) returns at A. It will be specimen, with the apex cut off. A vigorous spider
evident from this that however great the re- will soon project its head through the aperture.
sistance may be at O, sufficient current will flow When in this position it should be blocked behind
round the field magnets through the shunt C. with cotton wool slightly wetted. The cone can
to enable the dynamo to give the due amount of then be gummed to a slip, apex upward.
Many insects can be arranged in the same way
current, and moreover, by proportioning the re- for the observation of facial movements, and such
sistance of the shunt to that of the outer circuit, front views admit of interesting and extended study,
any possible fraction of the total current may be the action of the antennæ, palpi, and various organs
sent through the outer circuit.
of the mouth may be watched, and curious effects
produced by the excitation of the saccharine or
nitrogenous juices, administered from the top of a
sable peneil.

The

Bacteria Experiment.-During a recent lecture in the Philadelphia Academy of Pharmacy, glass jars were passed around containing samples of cultivated disease germs. Potatoes cut in halves had been lightly smeared with a coating of substances

Attached to a coil capable of giving a fin. spark, using a shunt of about 1 ohm resistance, our dynamo will light up a Gassiot's vacuum tube 3ft. long by turning the handle about 80 times a minute, and this without any fatigue. Since the resistance of No. 36, soft iron wire is An 8in. uranium "fountain" tube is brilliantly very nearly 1 ohm to the foot, it follows that by lighted when attached to one of the litt in. making five helices of the said soft iron wire, in spark coil advertised in our columns. lengths increasing from 1ft. to 5ft., and inclos- sparks given between carbon points with the ing these in tubes, as above described, we pro- dynamo in conjunction with in. spark coil duce a series of rough resistance coils of from are extremely dense and brilliant. Care must be 1 ohm to 5 ohms approximate, which may be taken in performing these experiments with the labelled with their several resistances, and used coil and dynamo that shocks be not inadvertently as shunts as occasion may require. Whichever given to those who may assist in hanging the shunt be used, it must always be so connected to tubes, carbons, &c., as they will be nearly sure the dynamo as to complete the circuit between to break the apparatus; for, owing to the high the armature and field magnets, while the outer tension of the current given off by the dynamo, or working circuit (which now becomes a derived the shocks inflicted by the coil are extremely circuit) is fed from the binding screws connected severe. A very pretty experiment, illustrative with the armature. As it is of importance that of the power possessed by the rays of high reTenacity of Tubercle Bacilli. It has been the student should thoroughly understand this frangibility, which abound in the electric light, doubted whether the sputa of tubercular patients, of evoking the phemomenon of phosphorescence, is to arrange the dynamo in connection with the

• All rights reserved.

containing germs. The bacteria were nourished on the moist surface of the potato, and presented very interesting appearances. Different results were obtained from different bacteria. Some of the half potatoes were covered with an ordinary deposit of mould. On others the disease germs had developed into thin, peculiarly-shaped patches of fungous growth of bright blue, red, yellow, and greenish colours. Others had grown into an intricate and extensive network of fuzzy fibres, the growth on the surface of two or three potatoes reaching over and covering a space having a diameter of 8in.

or 9in.

• From The Microscope.

exclusively used for hard porcelain. 4. The salt glaze which is produced in common earthenware by the evaporation of common salt during the burning. Its qualities are well-known. The glaze for pottery ware which is free from lead. The material is clay, feldspar, and borax. The preparation includes the calcination of the clay, during which it becomes red, and the draining and heating of the feldspar. Both these materials, as well as the borax, are finely powered and mixed. The preparation is 75 parts borax, 37 parts feldspar, and 37 parts clay. For the complete mixing of these substances it is necessary to melt them together and then again to pulverise them. The mass is somewhat difficult to melt, and must be exposed to the fire as much as possible. According to whether the ware is much or little burnt, the glaze has to be used in a more or less concentrated state, but as a rule the strength of 70° B. is sufficient. The time occupied in the burning is rather more than in the case of a good lead glaze, and must not be abbreviated. This glaze is somewhat more expensive than the lead glaze, but is of superior appearance and durability. Besides being harmless in itself, it resists acids and lyes.

ALLOYS USED FOR COINAGE.-III. By Prof. W. CHANDLER ROBERTS, F.S.A., Chemist of the Royal Mint.

(925), when heated to low redness in a muffle, be-
comes uniformly grey-white, while intermediate
tints are produced by heating lower alloys, until the
standard used for the French subsidiary coinage
(835) is reached. As this becomes quite black under
the treatment, the process ceases to be useful for
alloys of lower standard.

In very early times, the need must have been felt
of some chemical method of isolating the precious
metals-of separating them, that is, from their base
associates, so that the gold or silver, when purified,
could be weighed, and the amount originally
present in the mass deduced by calculation.

64

The crude method of assay, already described, which depends on the change of colour produced by oxidation of the baser constituent of an alloy, leads up to the method used from very early times, which also depends on the principle that precious metals will resist oxidation, while the metals with which they are usually associated will not. Its main outlines may be indicated as follows. When lead is melted with free access of air, a readily fusible substance forms upon its surface, This substance may be allowed to flow away, or, if the metal is contained in a suitable porous receptacle, called a cupel, the fusible oxide sinks into this containing vessel; in either case the oxidation of the lead affords a means of separating it from precious or inoxidisable metals, if any be originally present in the lead. I found lead in the ancient ornaments both of gold and silver, which Dr. Schliemann permitted me to analyse, and Pliny teaches that the T degree of purity tn go for ascertaining the of gold and silver, for he says, HE want of a method for ascertaining the Roman metallurgist used lead for the purification excoqui non potest, determining the amount of precious metals present nisi cum plumbo nigro aut cum vena plumbi." The in their alloys, must have been felt as soon as the greatest of the early alchemists, Geber, who died in use of metals for currency was established. The A.D. 777, knew perfectly that the lead acquired a history of assaying has yet to be written, but in new weight" when heated in air, and I have elserapidly reviewing the methods of assay which have where tried to show how important the recognition been practised, or proposed, it will be well to con- of this fact was to the whole fabric of modern chesider them in an order that is in the main chrono-mistry; it is not a little interesting that, among the logical, but which enables the physical methods, as very first experiments recorded by our own Royal distinguished from the chemical, to be dealt with Society, is a metallurgical series relating to the first. The nation for which the honour of striking weight of lead increased in the fireon the "copels" the first coins is claimed, gave its name to the at the assay office in the Tower, the account be"Lydian stone," or, as it is called in more recent ing brought in by Lord Brouncker, in February, times, the "touchstone." It is a dark basaltic 1661. rock, of fine texture, upon which a fragment of precious metal readily leaves a streak when drawn over its surface. The comparison of the streak left by the gold to be tested with similar traces derived from alloys of known standard and composition, afforded a ready means of ascertaining, approximately, the fineness of the metal under examination; while further insight into the character of the alloy was gained by submitting the streaks to the solvent action of an acid. There is an abundant literature showing the degree of accuracy that may be attained by means of this stone; its use has survived for approximate assays until the present day.

Then, again, there was the method of ascertaining the purity of metals by their density, as compared with that of water, devised by Archimedes, B.C. 212, which is applicable to both gold and silver, and is still often resorted to when the metal to be examined must be preserved intact. The usefulness of density, as affording a trustworthy indication of standard fineness, has often been pointed out, notably by W. Symonds, in 1756, and more recently by Dr. O. Broch. The possibility of ascertaining the standard fineness of alloys by the aid of electricity long ago occupied the attention of physicists. In 1823, Becquerel suggested that trustworthy indications might be afforded by the electro-motive force developed when the alloy to be tested is placed in an exciting fluid together with an alloy of known composition. The subject was partially investigated by Oersted, in 1828, and its practical importance was further pointed out by Gay-Lussac in 1830. In 1878, the use of magnetic induction for indicating the composition of alloys was suggested by Professor Hughes, who showed incidentally that the induction balance affords a ready means for detecting counterfeits, and I have elsewhere pointed out the degree of accuracy of which this instrument is susceptible. The method which involves the use of the spectroscope also deserves mention here, although it is, as yet, more delicate than trustworthy. These physical methods, both ancient and modern, are open to the objection that the uncertainty of the results they afford increases with the complexity of the alloys under examination; and further, the indications are complicated by changes in the physical state of the metals, produced either by hammering or annealing, Pliny states that in his time a method was in use for estimating the amount of silver in an alloy of silver and copper, by the degree of discolouration or blackening which attends the heating of the alloy in air. This method, long practiced in France, and known by the name of essais à la raclure (scrapings), or à l'échoppe, is described by Rochon, who says that it was generally recognised in the Roman mints in the time of Marius Gratidianus, triumvir of the money, and later by Chaudet, who gives a table showing that silver of the English standard

* An abstract of the Cantor Lectures, delivered before the Society of Arte,

The interest of the art of assaying, from a purely scientific point of view, was generally admitted in the 17th century. Lazarus Erckern, for instance, described it as the very inlet and mother of many other honourable and profitable sciences, while William Badrock, apparently regarding the art as an element of general culture, pleads its claims to be studied by all gentlemen."

has lost is noted, and, if it is considered that the result of the trial is inaccurate, or "too much metal has been lost, say by the boiling, or by being cared off in the lead," then it is to be repeated.

The amount of metal which has, for at least twe centuries, been taken for assay is 12 grains troy, sad this weight, which is known as the "assayer's pound," has the same number of divisions as the troy pound; the fineness of any given weight of metal is, therefore, indicated by the results of an assay, without tedious calculation.

With regard to the apparatus required:- I Geber's work "Of Furnaces" there is no mention or illustration of the "muffle" furnace, so that be seems to have conducted the process in a cupel surrounded by incandescent fuel. Biringuccio (15409 gives illustrations and detailed descriptions of appliances which hardly differ from those now use, and so does his contemporary Agrica Budelius (1591) gives a drawing of a furnace which somewhat resembles the type still used in Continental mints, except that the muffle, or oven, is places close to the base of the furnace; and the "Scutptures" of Sir John Pettus, reproduced from t works of Lazarus Eckern, show various forms of muffles and furnaces, some used by the ancient assayers, others adopted in the middle of the 176 century at Nuremberg, where the goldsmithsflourished so vigorously. He also gives an improved form of furnace, "made of armour plates," closely corresponding in its general arrangement with a furnace now lent by the Mint to the science collertion at South Kensington, which is specialty interesting, as tradition points to it as being the furnace used by Sir Isaac Newton in his experimenta on cupellation when Master of the Mint.

With regard to the balances employed, it may be sufficient to point out that, for centuries, they have been constructed with great delicacy, and that they now turn with oths of a grain, when loaded with 10 grains. In fact, the use of the balance is very early times, for the purpose of assay, absolutely demolishes the claim of quantitative chemistry to he considered of comparatively modern origin. The indications afforded by the balance as to the resa it of an assay are not absolute, as the process is linke to error from several sources, and needs to be controlled in the manner which will be described subsequently.

The point to bear in mind at this moment is, that if the silver has been associated only with readily oxidisable metals, especially copper, as is usually the case when silver coins are assayed, then it only becomes a question of providing the amount of heard necessary to furnish, by oxidation, sufficient litharge Having shown the great amount of interest to dissolve the oxides and carry them away. attached to the subject, I will now return to the however, the silver is associated with gold, tân actual practice of the art as a metallurgical opera-latter metal resists oxidation, and will remain on the tion. cupel with the silver, for-again to quote Geber-t Geber, the Arabian, gives, if Medieval transla- will in "nowise forsake it." The cupellation stage tions of his works are to be trusted, a sufficiently must then be supplemented by a "parting" operation accurate description of the process to enable it to be that is, the silver must be dissolved away by Me conducted at the present day with no other aid than solvent which will leave the gold untouched, his; but it must be remembered that it was the for this purpose nitric acid is universally employed object of the alchemist to distinguish silver from If the silver coutains but a minute quantity of gold, and to isolate the metals, rather than to gold, the presence of the latter will be indicated determine the amount of one metal present in a few specks of brown powder left at the bottom of admixture with another. Geber calls the process the vessel in which the silver is dissolved; if, bowof cupellation the trial of the cineritium, and he ever, the silver contains about one-third of t points out, in the course of a description that mass of gold, and has been extended into a strip, deserves to be reproduced here, that there are the gold will remain after the action of the acid, as two bodies perfect, abiding the trial, to wit, sol a coherent band, retaining the original form of the (gold), and luna (silver). Take," he says, "sifted strip, but much reduced in volume. This action of ashes or calx, or powder of bones of animals nitric acid on an alloy of gold and silver was certain i calcined moistened with water, and known to Geber and the early alchemists, but the tim make the mixture firm and solid with your hands, official mention of the use of the parting assay apand, in the midst of it, worked into a round flatish pears to be in a decree of Philippe de Valois, in the lump, make a round and smooth hollowness, and year 1343, confirming its use in the French Mind upon the bottom of it strew a small quantity of glass The assay methods for silver and gold are analo beaten to powder, which lay to dry. When dry, gous, in so far that both are purified by the action put your metal into the hollowness thereof, which of a solvent, but the base metals are removed from you would try to prove, put coals of fire upon it, silver by fused litharge, while in its turn silver is then blow with bellows upon the surface till the parted from gold by uitric acid. There is, then, metal flows: upon which, being in flux, cast part this difference between the assay of gold and silver. after part of lead, and blow with a flame of strong In the case of the cupellation assay of silver, he ignition;" this is to be continued until the lead button of metal has only to be removed from the is vanished," and precious metal is left still or cupel, and when the adhering bone ash has been quiet, and you see it clean and clear in its super-removed by a brush, it passes direct to the balance fices," that is, the lead has dissolved the oxides of The process would also be sufficient for gold, if t the base metals, and has carried them into the cupel, contained no other precious metal; when, however, leaving the gold or silver, or an alloy of both, in the the problem is to ascertain by assay how much gewei form of a button on the cupel. is contained in an alloy, which may contain silver, This operation, as described by Geber, would or platinum and other metals of similar properties more nearly correspond to a refining operation con- then care must be taken that the amount of gold ducted on a large scale, with a view to the extrac-believed to be present in the alloy does not exceed tion of silver from lead, rather than to the method of assay as practised at the present day on a few grains of metal.

The method of conducting assays, on what would at the present day be considered to be a very large sample of metal, seems to have been held to be necessary in the 12th century, for in the official trials of the coin in the time of King Henry II., 1154-89, the "Miles Argentarius" and the "Fusor" are instructed to take before the Barons of the Exchequer a pound of "twenty solidi" of the coin, which they are to place on a vasculum ignitorum cinerum quod in fornace est." The metal resulting from the trial is ther weighed, and the amount it

the one-third part of the mass, as a larger proporon of gold would protect the alloy from the solvent action of the acid, and the greater the

nount of gold, the less perfect would be the attack of the acid. In any case the first stage of assaying a gold alloy, say a sovereign, is to melt it with such an amount of silver as shall yield a butt containing rather less than one-third of its weight of gold.

For the sake of convenience, and for the incidental advantage that the solvent action of faced litharge removes copper and other impurities, the first stage of the assay of gold is conducted on a cupel, the object to be attained being mainly

rolled without fracture.

secure a button of gold and silver in a convenient check may indicate the presence of too little or too
fort for submitting to the subsequent operations. much precious metal.
The alloying stage would, however, be just as The objections to the use of a standard silver
effective if it were conducted in a small non-plate are far greater, as the alloys used for the
porous receptacle, such as a small crucible of silver coinage, in this and in other countries, are
glazed porcelain.
mechanical mixtures, the molecular arrangements
The subsequent operations are, flattening the of which are very peculiar, and so far as my ex-
button, annealing it, rolling it into a strip, and perience goes, a plate of the legal standard cannot
anuealing it a second time. It is then coiled into a be prepared of uniform composition. With regard
spiral, or cornet, and treated by two successive to the use of pure gold and silver plates, it should
portius of Litric acid, in order to remove the be pointed out that, if it were possible to obtain
silver; after this the spiral of spongy gold, which gold and silver of absolute purity, there would be
retains the original form given to the silver-gold no limits to accuracy in assaying, except such as
alloy, is heated to redness, when it becomes bright, arise from operations of a purely mechanical nature.
and is sometimes so coherent that it may be un- Of course, it is not possible to attain a chemical
purity, and the presence of traces of impurity in the
checks causes the results of assays made in com-
parison with them to indicate the presence of an
amount of pure metal in excess of that actually
present in the alloy; but as the converse can never
be the case, that is to say, as the gold cannot be
more than pure, no danger can arise from this
cause, and the error can be easily allowed for.
The supplementary fine gold and silver plates,
prepared in accordance with instructions I received
from the Lords Commissioners of the Treasury in
1872, proved eminently satisfactory. I have not
been able to prepare, or to obtain from any source,
gold of greater purity, even in small quantities.
The silver plate leaves little to be desired, although
it is not quite as pure as silver prepared by M.
Stas, in comparison with which it is as 999.95 to
1,000.

This is an outline of the processes of assaying: the precautions which are adopted with a view to secure accuracy remain to be considered. Inaccuracy in silver assaying mainly arises from loss of silver, which may disappear in small but variaable quantities, either by volatilisation or by sinking into the cupel with the litharge. The amount O metal lost varies with the temperature, which is never uniform throughout the muffle; and the results of assays, as indicated by the balance, have, therefore, to be controiled by assays on pieces of metal of known standard, distributed in such a way as to represent the varying degrees of temperature throughout the muffle. The metal lost by any given check-piece is added to the assays in close proximity to it, and, as the amount of metal lost very ofteu amounts to 1 per cent., the apportioning of the additions to be made demands great skill on the part of the assayer, who has also to decide from the appearance of the buttons whether they have retained lead or not, in which case they would, of course, be unduly heavy. In gold assayiug, on the other hand, although as Geber knew, gold resists the action of molten litharge better than silver does, some precious metal may be lost ither by volatilisation, or by retention in the cupel, but the chief sources of error are (1) solution si gold in the acid used, which would reduce the weight of the cornets, and (2), retention of silver by the cornets; but these inverse causes of error may be combined, without neutralising each other. Some means of checking the results must, therefore, be provided, and it would appear that for centuries implicit confidence has not been placed in the indications afforded solely by the assays, as comparisons have invariably been instituted between the pieces of metal taken for assays, and standard trial plates, or pieces of known composition, assayed side by side with the coins, so that

In conducting official trials of the pyx, minute accuracy is secured by a final appeal from the standard plates themselves to pure gold or pure silver.

We are now in a position to consider another question, the importance of which has long been recognised by law, and that is, the difficulty of attaining an exact standard, either of weight or fineness, in the case of all the individual coins issued from a mint. The law has for centuries, and in all nations, permitted a certain deviation from the exact standard. The amount of such "remedy," as it has always been termed in this country, has changed from time to time, but has gradually diminished as the art of coining has advanced.

have joined the Latin Union have also a remedy of 15th. In America, the remedy in the case of the gold coins has been reduced to 100th. It is certainly not the opinion of Mint officers at the present day that the remedies should be reduced to the lowest possible point, as this would involve the rejection and re-coinage of a large number of pieces before they could be permitted to leave the Mint; but, on the other hand, all agree that a persistent variation, however slight, above or below standard, has never been contemplated by law. The effect of such a mean variation would be remarkable. If, for instance, the Mint were to issue sovereigns which were either persistently too rich or too poor in gold, to the extent actually permitted by law, a loss or profit would accrue of over £2,000 on each million coined, and a persistent variation of only 10th part would be equivalent to a profit or loss of £100 a million. In Mint practice, at the present day, even this comparatively small variation should be avoided, and the public trials of the pyx prove that it does not exist.

I have dwelt on these facts because the maintenance of rigid accuracy in the operations of coinage becomes of great importance in internationa! currency. One Government might, as the late Professor Stanley Jevons pointed out, "coin money slightly inferior to the proper standard, and such money once introduced would, in virtue of Gresham's law, be difficult to dislodge." I admit, with him, that it is hardly to be supposed that a State issuing money under international obligations would wish to make a profit of one or two parts in a thousand, which the remedy would legally cover; but nevertheless, the degree of accuracy with which the coinage is executed would be of much importance, for the following reason. A nation would be bound by the International Convention to withdraw and re-coin such coins of other nations as might be circulating within its borders at the time they were reduced by wear below the lowest weight at which their circulation would be legal, and it follows that any deficiency of standard which might exist would have to be made good by the nation on whom the re-coinage happened to fall, and a nation coining with rigid accuracy would suffer from the shortcomings of those who did not.

any error affecting the coin assays also affects the Saint Louis, of France, 1253, who granted an / Scholarships of the value of £150 have been awarded

check pieces, and, therefore, the error can be

allowed for.

the alloy may not bear to each other with mathe-
It follows, that although the component parts of
matical precision the proportion-prescribed by the candidates successful in the competition for the
The Whitworth Scholarships.-The list of
regulations under which they are manufactured. Whitworth scholarships, 1884, has been issued:-
they may, nevertheless, be considered to be of Richard Stanfield, engineer apprentice, Manchester,
standard fineness. The earliest reference to a has obtained a scholarship of the value of £200
"remedy I have met with is in the reign of
allowance of carat, for the fineness of louis d'or: Denning, engineer apprentice, Crewe; John Reeves,
to William Sackville, engineer, Crewe; Tom H.
The Mint agreement between King Edward I. and
engineer, Crewe; André P. Griffiths, engineer ap-
prentice, Ebbw Vale (Mon.); Richard North,
engineer, Manchester; George Coates, engineering
draughtsman, Full Sutton, near York; Andrew C.
Shaw, engineer, Glasgow; and J. Kerr Reid,
mechanical draughtsman, Glasgow. The following
have obtained scholarships for £100 each:-Robert
L. Clarke, draughtsman, Plumstead; John Kemp,
engineer apprentice, Glasgow; Thomas A. Peace,
engineer apprentice, Manchester: George A. Shaw,
engineer, London; Albert E. Wolstencroft, joiner,
Oldham; William A. E. Crombie, marine engineer,
Glasgow: John Sharp, draughtsman, Glasgow
Henry J. R. Burstall, engineer, London; Edwin
Baggs, engineer student, Bristol; William J. Caiger,
engineer, London; Edward Gardner, engineer,
Manchester; James Nixon, engineer apprentice,
Newcastle-on-Tyne; John Dougan, engineer, Glas-
gow; Herbert B. Gregson, engineer, Sidcup; James
Tasker, draughtsman, Accrington; and Frank
Brown, draughtsman, Plumstead.

ment at the International Monetary Conference,
held in Paris in 1867, said, "the remedy is not an
arbitrary stipulation, but is the limit of errors
which belongs to every thought, to every chemical
analysis, to every composition of alloy, and as such
depends on the precision of the balances, and the
methods employed in the fabrication of money. It
may be determined rigorously by applying the
calculus of probabilities."

An examination of a series of assays made of the William de Turnemire, in 1279, provides a remedy trial plates shows that, although the standards of of 24dwt. on the pound troy of the silver coins. Aneness were always prescribed by law, the plates The law does not appear to have contemplated have, kevertheless, at times been very inaccurate. that the "remedy" should be systematically made The imperfections of the gold plates are mainly use of as a source of profit, either to the Crown or due to sources of error which had been recognised, to the Master of the Mint; it was rather considered but which were ignored when the last plates were to define the limits within which occasional varia ade, and it is well to explain, therefore, that tions of standard weight were unavoidable, and its stes were, in former times, authoritatively pro- true function has been well defined by the late M. nounced to be "standard" simply with reference de Jacobi, who, representing the Russian Governto the results of an inaccurate process of assay. The process now consists in submitting an acculy weighed portion of the alloy to a rapid method of chemical analysis, whereby impurities are eliminated, and the precious metal, thus puriied, is again weighed; but the method is complicited, and the accuracy of the result may be affected by the retention of impurities, or by an actual loss of metal during the process. The weight of gold as indicated by the balance will, in con- The Mint indentures have been drawn up in just quence, not represent the amount originally the same spirit. Remedies were accorded because prescat in the alloy, and it is, therefore, necessary the said moneys may not continually be made in all to control the results by assaying, side by side things according to the standard, but, peradventure, with the alloys under examination, "standards" through default of the master or workers, they or check-pieces the composition of which is known. shall be found sometyme too strong or too feeble in 4, however, any error in the composition of these weight or alloy," but this has not prevented a very checks will be reflected in the result of the assay, it different view having been taken of the privileges is preferable to use pieces of pure metal corre-accorded by them, both to the Sovereign on the one sponding in weight to the amount which the alloys hand, and the Master of the Mint on the other. to be tested are anticipated to contain. Formerly, Queen Mary, for instance, seems to have considered such checks of pure metal were not employed, and that the Sovereign was entitled to add as much a small amount of silver varying from th to base metal to the coinage as the law permitted, the 1th part of the initial weight of the assay piece sum so derived after deducting coinage expenses, to which remained in association with the gold was be considered seignorage; but she held that the consequently reckoned as gold in the assay report. Crown could not debase the coin, or increase the It follows, therefore, that even the more recent amount of base metal in it for private ends. plates, when accurately assayed, are usually found to be sensibly below the exact standards which they were intended to represent.

With regard to the action of Mint Masters in this respect, the history of the coinage abundantly proves that they frequently availed themselves of the "remedies," viewing them as a legitimate source of profit, or as a means, incidentally provided by their contracts, for reducing the current expenses of working, the best known case being probably that of Lonison, Master of the Mint in the reign of Queen Elizabeth.

The experiments made with a view to ascerta. the composition of the standard gold plate prepared by me in 1873, show that the greatest variaou of this plate from the exact standard does not exceed the 18th part; but the use of even a fairly accurate standard plate is liable to be attoned with error, as the actual amount of The scale of remedies is fixed by the Coinage Act precious metal in the amount taken for the check of 1870, at present we will only consider the remedy piece may exceed or fall short of the true standard. of fineness, which, in the case of the gold coin, has It follows, therefore, that the assay reports on a range of+th, and in the case of silver portious of metal tested by comparison with this +1559th. The gold coins of the nations who

Graphs.-The French Ministry of Public Works publishes a formula for a hectograph, or gelatine pad, which is very near the original recipe published in these columns. The composition consists of 100 parts of good ordinary glue, 500 parts of glycerine, 25 parts of finely powdered baric sulphate, or the same amount of kaolin, and 375 parts of water. For the copying ink a concentrated solution of Paris violet aniline is recommended. To remove the old copy from the pad, a little muriatic acid is added to the water, washing it gently with this liquid by means of a soft rag, afterwards using blotting paper for removing superfluous moisture.

AT a recent meeting of the Royal Society of Dublin a paper was read by Prof. G. F. Fitzgerald, M.A., F.R.S., hon. sec., "On a Non-sparking Dynamo." By applying the principles of Maxwell's modification of Thomson's electrical doubler to a dynamo in which the current passes through two or more coils in parallel circuit, it is possible to arrange the magnetic field and the brushes 80 that when the terminals of any coil come into contact with their brushes, the terminals shall be at the same difference of potential as the brushes, and that when they break contact there shall be no current running in the coil, thus avoiding all sparking. The energy of self-induction usually wasted on local currents and sparks will in this case be spent in producing useful current.

AUG. 15, 1884.

SCIENTIFIC

ENGLISH MECHANIC AND WORLD OF SCIENCE: No. 1,612.

NEWS.

HE large gold medal of the Royal College

TH of Surgeons, which has been previously

given only six times since its institution in
1800, was last week awarded to Sir Erasmus
Wilson, only just in time for the distinguished
dermatologist to receive the news before his
death, which occurred last Friday. The medal
was conferred "in recognition of his great
liberality in his contributions to the museum, in
his endowment of the pathological curatorship,
and in his foundation of the professorship which
bears his name." Mr. Erasmus Wilson studied
at Aberdeen and London, and became a member
of the Royal College of Surgeons in 1831.
1869 he founded the chair of dermatology and
established the Museum of Dermatology in
the College. He commenced his professional
but
anatomist,

life as

an

soon

In

with meals during the twenty-four hours. The LETTERS TO THE EDITOR.
French certainly have peculiar methods of keep-
ing the cholera away.

The Falmouth Meteorological Observatory is to have a suitable building, urgent representations having been sent round, and large subscriptions promised. The foundation stone was laid on Tuesday.

We have received Vol. II. of the "Abstracts of Proceedings of the Liverpool Astronomical Society," and Nos. 2 and 3 of the Transactions. No. 2 contains the reports from the sections, and No. 3 is the catalogue of the magnitudes of 500 stars in Auriga, Gemini, and Leo Minor, from photographs taken with the equatorial stellar camera by Rev. T. E. Espin.

The

[We do not hold ourselves responsible for the opinions of our correspondents. The Editor respectfully requests that all All communications should be addressed to the EDITOR C communications should be drawn up as briefly as possible.] the ENGLISH MECHANIC, 31, Tavistock-street, Coven-garden w.c.

All Cheques and Post-office Orders to be made payabis vi ** In order to facilitate reference, Correspondents, whm J. PASSMORE EDWARDS. speaking of any letter previously inserted, will lige by mentioning the number of the Letter, as well as the page on which it appears.

"I would have everyone write what he knows, and as much as he knows, but no more; and that not in than only, but in all other subjects: For such a person may nature of such a person or such a fountain, that as to have some particular knowledge and experience of the other things, knows no more than what everybody does, and yet, to keep a clutter with this little pittance of hie, from whence great inconveniences derive their original. will undertake to write the whole body of physicks; a vice -Montaigne's Essays.

THE AFTERGLOW - ALCOHOLIC BEVERAGES-SPURIOUS CRESCENTS OF VENUS-A REPLY TO AN APPEAL -BETA CYGNI-THREAD WEATHER GUIDE.

One of the Bennett-Mackay cables has been successfully laid and signalled through, and the Faraday left with the other last week. company expect to be ready for business early became in the fall, but they will not start until everyknown as a specialist in skin diseases, to thing is in good order, and they are able to offer THE SUPPOSED SATELLITE OF VENUS the literature of which he was a voluminous the public the best possible service. It is now and most distinguished contributor. Partly from quite probable that another cable will be laid his books, but mainly from his practice, hević Iceland and Greenland to Labrador or Newamassed considerable wealth, which he freely foundland. distributed in works of charity or beneficence. Londoners owe to his prodigality the presence of Cleopatria's Needle on the Thames Embankment. In 1881 he received the honour of knighthood. and occupied the chair of the Royal College of = Surgeons. Sir Erasmus was born in 1809, and was consequently in his 75th year.

The death is also announced of Mr. Charles Manby, the builder of the Aaron Manby, the first iron steamer that ever went to sea, and for nearly half a century identified with the Institution of Civil Engineers. From 1839 to 1858 Mr. Manby was paid secretary, and on his retirement he was presented with a testimonial of plate and a purse containing a large sum of money-a pleasant episode in his life which was repeated in 1876 as an acknowledgment of his gratuitous services as hon. sec., a post he con

tinued to hold to the time of his death.

Mr. John Aitken, of Urmston, a well-known Lancashire geologist, who had twice filled the office of President of the Manchester Geological Society, is also dead, at the age of sixty-four.

The French Association for the Advancement of Science will meet at Blois from Sept. 4 to 11

next.

The British Pharmaceutical Conference, which used to be held a couple of days in advance of the British Association, and at the same place, was this year held at Hastings-Canada being rather too far. The Pharmaceutical Chemists are an important body in the commonwealth, and deserve more recognition than they receive from the profession and the public. The conference issues a Yearbook, which is an authentic record of the progress of pharmacy, of new processes, preparations, and formula.

On the Liverpool and Manchester section of
the London and North-Western Railway, some
of the trains are now lit by Swan 20 candle-power
lamps. A Brotherhood engine on the tender
drives the dynamo, and near the driver's hand is
a regulator fitted with a lamp showing the candle-
power of those in the carriages. Each compart-
ment has duplicate lamps; in the event of accident
to one, the other is instantly made incandescent.
In this column (April 25) we announced that
the Oregon had run out to New York in 6 days
9 hours 22 minutes. She has just come home in
6 days 12 hours 54 minutes, the distance for
timing being Sandyhook to Daunt's Rock
Lightship.

a

There is nothing like perseverance, but it seems hopeless task to attempt to trade regularly with the stations at the mouths of the great Siberian

M. Sibiriakoff

rivers. For the "last time"
despatched the steamers Nordenskjold and Obi,
but the former broke down when nearing Kara
Straits, and was towed back to Vardo.

Mr. Robert Galloway contributes to the Journal
"Emerald Green," in
of Science a paper on
which he shows that the arsenical poisoning
supposed to arise from green wall paper is a
myth.

66

[23128.]-I HAVE to thank Mr. Sadler, once again, for what he says in letter 23067 (p. 487). I have no doubt he is right; but he will, I think. you have to make believe agree with me that (like the Marchioness in "The to persuade yourself that the two Old Curiosity Shop") very much Fontana's drawings, on p. 345, in any legitimate queer little spheres shown in his reproduction of sense, present "la même phase que la planète." Nay, there are a couple of them which, in the aesthetic slang of the day, is too-too!

66

as your corre

the dust from the Javan mountain, after permanently settling down in our atmosphere, should again be stirred up a year after the catastrophe in which that most gallant-but proverbially confiding-secit had its origin, seems to me a story to be related to Petermann's Mittheilungen contains a paper tion of Her Majesty's forces who serve part of their Either "T. B. C." (letter 23071, p. 488) is unby Prof. Mohn on the Siberian Polar Sea, in time afloat. These are affected, to read the New Testament in the original, or he is which he discusses the Vega records of tempera-acquainted with Greek, and hence wholly unable ture and salinity of the sea. to a large degree, by the warm waters of the scarcely arguing ingenuously. Imprimis, I contend Siberian rivers. Lieut. Hoogaard contributes a that Oivog always is employed by Classical writer In the next paper on the Kara Sea, in which he contends to signify fermented wine; in fact, the Greek verb that the quantity of ice is approximately the same Oivo, which signifies to intoxicate, or make place, in quoting John ii. 10 my reference was no 46 τὸν καλὸν οἶνων, each year, but that it shifts its position accord- drunk, is directly derived from it. to the words ing to the prevailing winds. Will T. B. C." spondent must very well know, but to the sequent ones καὶ ὅταν μεθυσθώσι.” look out-or get some friend to look out-the Fanatics who demand that mankind generally shail meaning of Moro in the first lexicon at hand relinquish the use of what in moderation is pleasant, useful, and beneficial because a minority grossly The committee appointed to inquire into the A Marsh Beneath the Sea.-Every south-abuse it, should be quite sure that they are in a experiments of M. Pasteur with the virus of hydrophobia, report that his statements have east and southerly storm throws upon the south position to quote correctly when they appeal to been entirely borne out. Inoculation with the side beach of Long Island large masses of peat, Sacred authority in support of their "fad." While attenuated virus of hydrophobia gives a dog lignitic branches, trunks of trees, fossilised leaves, on this subject, I should just like to say, in conimmunity from the disease, just as simular treat- and animal remains. The coast, it is said, after a nection with letter 23100 (p. 511) that while I ment preserves a sheep from charbon. All the heavy wind and surf, is strewn with these appar-quoted from Phil. iv. 5 from memory, and without Water Island. The geologists state that the ap- that kis has the very rigidly limited meaning 23 dogs submitted by M. Pasteur as having been ently unaccountable objects from Atlanticville to turning to the book at all, I can scarcely admit thus inoculated have resisted the strongest virus on inoculation, whereas the majority of the 19 pearance of débris seems to be the result of the attached to it by "M." I never dreamt of myself wave action of the surf upon the remains of a vast applying it solely to the gratification of the senses. swamp, at present submerged beneath the Atlantic. Eikia signifies moderation or mildness quite non-inoculated dogs have succumbed. Of the latter, six were bitten by mad dogs, three of them After due calculations they have decided that this as much as it does equity. Even, though, acceptbecoming mad, [eight were subjected to intra- submarine swamp extends fifty miles longitudinally ing your correspondent's rendering as a literal one, venous inoculation, all becoming mad, and five to and half a mile latitudinally. Professor Newberry, I think it not wholly inapplicable as a precept cr inoculation by trepanning, all becoming mad. of Columbia College, gives the following explana- caution to the teetotalers, who would, if they The result is decisive; but the committee will tion of the existence of this marsh: "The coast is could, not only abstain from fermented liquors We find nolens volens, to do the same thing. now inoculate a large number of fresh dogs, and settling, and what had been swamped places on the themselves, but force every other human being, will compare these with an equal number of dogs land have been submerged by the waves. Long Island, evidences of subsidence going on at not inoculated. It will likewise investigate the along the coast of New Jersey, Staten Island, and In some places question whether, after a dog has been bitten, the present time, and that which was forest land inoculation with the attenuated virus will prevent and marsh land is now out at sea. any consequences from the bite. M. Pasteur the peat beds which were marshes on the land have will lay before the International Health Congress been submerged, and we find shell fish bored into at Copenhagen, results which, as the committee the peat. I have plenty of specimens to show that remark, are so honourable for French science, the level of the land has changed, and we have and give it a fresh claim on the gratitude of also fresh evidence of that circumstance in the faet mankind." The committee are Messrs. Bouley, that stumps of trees of a large size are found along Beclard, Bert, Tisserand, Villemin, and Vulpian' the coast at some distance in the water where they are only, perhaps, visible at low tide. They must have grown on comparatively dry ground."

Mr. Ballot's letter (23097) on p. 510 seems to me to observations-real or imaginary-by M. Callandreau of Venus in and near inferior conjunction, oʻ possess a peculiar interest in connection with the which I gave a short account in letter 20059 (p. 484), because here is an observer who sees this odc duplication of the planet's crescent and definitely traces it to atmospheric causes.

I am sincerely sorry that my little joke on p. 484 should even appear to have given pain to an esteemed fellow-student of science. Let me hasten to assure "Garrison Gunner" (letter 23121, p. 516) that I neither have, nor ever had, the slightest doubt that his statement of the facts of the case was essentially true. It is his interpretation of them which I question. I should like to know what "Sigma' has to say to it.

I do not wish to put Mr. Best (query 64329, p.