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j-tf.u-' p. 317), is exemiiletieU ... in llu- colours exhibited flrtro a bright poiDt is seen reflected oil or refracted ihrvneta a Mir/nee regularly striated ar aoratched a=r"»s wiih fine equidistant lines, an beautifully exhibited In the so oalled " Barton's Buttons' (from the autr of the ingenious and skilful amateur mechanic, Tao first executed them), bras* or steel buttons delicstcly cross lined by engine work." Are these buttons aaw pTocurable, and where ?—U. J. TV.

[2f.-210—"I>. H. G.*S" CUTTKK BAR.-In looking

vl "D. H. G.'s" working drawing of hla cutter bar,

irivon at page 306 of the English Mechanic of

DwtmW't 10.18»», it struck me that the patterns given

bad oi.e fault—viz., that the top of the cutting edges

of the cutter, stands above the centre of flexure of the

bar. Verhaps *• D. H. (x.," or some oneof yo:ir able

ci'itlaibutors, will kindly take the trouble, either to

.point out where ray error lies, or should I by chance

be risfct, to suggest n method by which the defect can

be remedied, otherwise than by lengthening the already

r-otnewnat long crank, by increasing the thickness of

ih<- bar, or by slteriu" the position of the parts In such

maimer, as will render it difficult to adjust the strap

truly to its work ?—r'oitEiGNEH.

tJOii.1—TO "F.E.A.!1."—May I bo allowed to nsk

o. few questions of our learned and ever-obliging

■* F.K A S." 1. How can I. wben I know the foci of

the C'Ustltueut len.-cs of a IJuyglionlan eyo-plcce. cal

cubiiu the powfr thereof? 2. What does he consider

the Finn I lest achromatic ref i acting aperture with which

live stars of tile trapezinni & Orlonis can be seen?

Would lie think a :iin. good, that would show tliejn?

:'.. .Some time ago, " F.K. A S." said, that a KJin. would

not divorco stars less thaa £'-5 apart, but according to

Ihillmeyer's formula (as given last week by the Rev.

T. W. Wcbbi, It should divorce a 6 mag. pair, only

\°-91 apart- Docs " F.R.A.8." tbink that It would not

do this? 4. Are the eye-pieoes used in reflecting and

refracting telescopes the same? 5. In viewing a star,

say a 7 «;.hn. achromatic, and power 7"0, would it not

present a disc larycr apparently than in a 3in.f and

power 259? Allow we to congratulate yon on your

Improved appearance onil si2e.—Scorpio.

rjira 1-SCJENCK QUESTIONS.-Our Scienco Department put some examination papers before us last year, wh'ch ltav*, I think, about !)> per cent, of our teachers in the fog. As onr English Mechanic does not like to see nor leave, any one in the fog, may I ask the followiug questions. 1st. In the plane geometry honours paper, show how to construct n triangle ABC, tho base A B being .'Sin., its height 1 75, and the sum of the sides AC+ B C =4 5. 2nd. Jn the building construction, the advanced paper contains some ancient specimens, which are very little known at the present time ; at least the correct dimensions are not known, nor are onr teachers or students in possession of any books which give the requisite knowledge, a»d therefore I should bo much obliged if you inform mc whether p. studeut is expected to show his knowledge v.i lunking a design similar to those given, or is he to show his acquaintance with the structures of which they give sketches. The latter is, t think, Impossible, as the dimensions given are not sufficient, nor do they correspond with the sketch. For instance, in the eketrh of St. Thomas's Church at Charlton (n), in the span of tho roof two lines are given, which appear equal on the sketch, but one is said to be 15ft. Sin., and the other oft. Oin.—Student In A Fog.

[«««■».]—PKOl'OKTIONS OF SPACE.—Can any brother reader toll me the proportion between the space occupied by :iny substance solid and when in balls? Or, to vary the question, if 6 cubic feet of lead weigh say 10001b., what weight of lead shot can be packedio a caseof similar dimensions?—Mxchanicub. [2«>5.)-BlKDS' EGGS.—I have a good collectioN of birds'eggs. How can I best preserve them, so that tbey may last as long as possible ?—Rustic.

p050]-AUCHIMEUES' LEVKU.—Some weeks agy 1 noticed a paragraph in our Mechanic, describing a machine said to possess the same properties as Archimedes' lever, invented by a working man. Though fctatcil t>> be very simple in construction, the working, as shown by description, was altogether unintelligible to my dull brain, and I could make nothing of it. Could any of your talented contributors give a short description of the real Archimedes' lever, and what wonders it was supposed to perform; nlso, if anything else has come to light about this new invention, which took nigh unto 40 years, according to report, to bring to perfection? Is it registered? A drawing would be very acceptable.—Rustic.

[2ff27.]-STf'AM AND WATER QUERY—My boiler water is heated by a patent ecouomiser 280°, <lrwen Into boiler by a force pump. Now, the steam in boiler is much stronger than in econoroiser. consequently It forces the water and steam back from the boiler. Can any of your very able correspondents give a panacea for this ?—Mancestrian.

p«28/]-T)lMENSIONS OF ENGINE. —Will any of your numerous correspondents kiudly set me right? I want a steam engine, 6in. stroke and 4in. bore, to "i|'kc 100 revolutions a minute with 501b. pressure. What 1 want to know is, what size the steamways ungnt to be, and what size the exhaust way ought to be; what size the steam pipe and what *izo the exhaust pice to work economically and right. Shall be thankful for practical information.—Cam.

[2629.3-TirEQUEKETT CLUB.—Will " W. H. G," wliu answered a correspondent iu relercnce to the t^iiekeit Microscopical Society, kindly inform me if I can obtain the Qutkrtt Joiu-nal regularly In Bristol, where I reside? I take the M.rriisnmir. Jtmrvnl Oiionxliiy) now, but should like the QiieUtt Journal also.—Ed. U. Jones.

[20.-iOJ-C.YNOE STRAKES.—The strokes of a canoe being of pine Jin. thick, how should thev be fastened together.' With rivets and washers, copper nails, or bra«s screws? Are the edges chamfered at »1, or left sqnare, and how niucli lap is necessary? '»Iso, what caulkiug or composition is used to reader th-canoe wnter-tight?—Thuee Ikqiirhhs.

C2«t.]—SPHERICAL FORM OF TnK EARTH. — Vt ill nny reader answer me the following query ?— S'ippnsc we have n cistern linlf a mile loi.g and 2fr. deep tilled with water, would the water be affected bv

the gravitation of the earth and form ft sweep, or would it keep perfectly straight in tho cistern, and at the same depth all the length?—Ajax.

[2632.]-BI.OTCHY FACE.-If "Kortunatus" will be kind enough to say in what quantity and how often tho mixture (for which be gives the recipe at bottom of page fill of No. 2fi:i of the Mechanic,) Is to be. taken he will oblige-T. 15.

[26330-RAISING WATER— Thanks to " Senex" for his answer to my question, but his plan does not meet my case. If any brother reader has any knowledge of the rope pump, and would give information of its advantages or disadvantages over the ordinary suction pump lor deep wells, he would oblige.—M'. S.O.

[2034.:-PAPER-HANGING—Will auy brother sub-criljer be kind enough to give a brief description of machinery for printing paper-hangings, with their probable cost?—A. R. K.

[2(135 1 —UNNOTICED QUERY. — PUMP FOR MODEL STEAM ENGINE.—Will nny klud reader please favour me by answering the query (21211) in No.

200 — HVOHALLICAN.

[263B.1-CEMENT FOR JOINING BOARDS.Therc 1b a cement In use at present for joining boards together. Could any of your readers suy where 1 could get It, or how to make it? Or is it possible to make qlue resist water? If so, by what means ?—One In A Fix.

USEFUL AND SCIENTIFIC NOTES.

INTERESTING FACTS, p. 6».—GERMAN MILE —The "Almannch do Gotha, edited at the well-known geographical Institute of JustuB Perthes, gives the following reductions:— 1 kilometer = 0*1347G^O geographical miles 1 aeograpbieal mile = 7 kilom. -4204:18 1 English mile = 1 kilum. 009315 = 0210876 goog. mile

1 Russian vcrste = 1 ktlom. 0C6781 = 0-1437025 geog. mile— Bern Akdin.

BALLOONING.—Mr. Coxwell has commenced his aerial voyages somewhat earlier this than he did last year. Oc the 12th inst. he ascended from the Gas Works at Hornsey, and travelled :J5 miles in an hour and a half—descending some miles beyond Chelmsford On the 7th ult. the aeronaut and his pupils made the iirst ascent of the season from the neighbourhood of Tottenham, the descent taking place four miles north of Bishop Stortford. The famous ** Nassau" balloon, built by the late Mr. Green, has duriug the winter undergone a thorough restoration by its present proprietor, Mr. Coxwell, who purchased it last .July. This celebrated balloon was made at a cost of £2I0>, being composed of the best Italian silk, manufactured by Mr. H. sSopcr, of Spital-square. Mr. Coxwell has recently had a fresh quantity made by the same linn at 18s. a yard, and ihe "Nassau" balloon will be soon available for further explorations. This was the balloon in which Mr. Green made hisjreiaarkable trip to Germany, and also the one employed to take up Cocklng'» para.-hute. Afterlts completion it will be inflated for exhibition. The veteran Green, who died recently, had determined, although 85 years of age, to accompany Mr. Coxwell In his first ascent this season, and he declared that the repairs n.id additions made by Mr. Coxwell would reader the "Nassau" as good and safe as ever.

SOMETHING NEW ON SILVERING PAPER — We find the fallowing in the last number (of the Canadian Journal of Photography;—" Always ready to lay before our customers anything new or valuable in photographic manufacture, we should not be doing our duty to them did we not describe a in ult; of silvering the paper which we have found of very great value; indeed, we have no hesltatiou in statiug that anyone trying the plan will ke very much pIeaso4 with the result. Provide a board slightly larger than the largest piece of paper you inleud silvering, cut pieces of white blotting paper oi the size of the board. Whon about f silver yonr puper, place the board in a convenient position near the silver bath, with one end elevated to an angle of say 30 degrees. Float your first sheet on the bath, and then place a piece of blotting paper on your board. When the sheet Is ready to lift from tile silver solution, lift it bv tho two corners nearest you, and draw the wet albumen surface ii gainst the eud of the bath; lift the sheet of paptr very slowly, and allow it to cling with its wet side tight to the end of tho tray. This it will easily do if you are careful to lift tho paper perpendicularly over the end oi the dish. You will thus wipe off, as it were, nearly every drop of tho free nitrate from the face of the paper, saving waste. The only precaution necessary at this stage Is to lift the paper slowly and straight up, so that it clings to the inside of the end of the disc. Now lay your sheot face up on the blotting p4per on your sloping beard, taking care th*t the end of the sheet that came last off the bath is laid on the highest end of the board. Prepare- a second sheet, and when nearly ready to lift off the bath, c;>vcr the sheet first prepared, nud now partially dry, with another piece v>t clean blotting paper, and lay the second sheet on top <>f this, as before. I'rooecd in like munuer with the rest, and when finished put. another board on top of all, aud allow to dry. The advantage* of Chis mole of proceeding are numerous—saving of silver, no messing and dropping round, perfect equality of sensitising, absence of measles, mealiness, spottiness, nnd all defects inherent to imperfect silvering; beautiful, brilliant t-urface when printed, aud your paper is always flat, if you try this plan you will find it cleaner, s'irer, simpler and better than auy o:h^r plan with which we are acquainted."

METHOD FOR OBTAINING A CONTINUOUS CURRENT OF AIR OK GAS UNDER PRESSURE, FOR BLOWPIPE AND OTHER PURPOSES.— Mr. T. L. Patterson, in a recent paper read before the Glasgow Philosophical Society,■explainedliow u continuous currcntof air or gas is obtained under ordinary circumstances by the mouth blowpipe or theioot-beilows, and th^n mentioned the chief objections to those two methods, and proceeded to describe a method which

ho had found to be free from those objection*. He snid that it was wellfadapted to blowpipe work, aud that he could easily obtain a pressure equal to half an atmosphere by means of it. The principle Involved is the same as the Catalan tdowpipe of Sprcagel, and is wrought in connection with a Bunsen filter-pump, although it may he erected separately. The air-tap of a Bunsen pump being opened, the water is turned off, and air passes with the water down a long pipe, of 30 to 35ft., in a continuous stream of babbles. By receiving the stream into a bottle or other vessel, made air-tight with a cork, through which two tubes are passed, one nearlv to the bottom of the vessel, and the other just through the cork, the water will flow off hy the deep tube, and airescupe by the upper; aud, by placing n stopcock on the upper tube, to regulate the escape of the air, the pressure in the vessel may be made equal to the height of the water tube. The apparatus as used by Mr. Patterson is made of sheetI«-ad and "comp»" pipea. A liquid may be boiled under the constant pressure of the apparatus bv placing it in a Btrong flask, and connecting the latter lair-tight) by meanu of a flexible tube, with the pressure stoptock ; or it may be distilled by connecting the receiver (made air-tight to the retort or distilling vessel) wl.h the pressure stopcock, as before. It will also be found useful for increasing filtration, by applying tho pressure on the surface of the ljquor to bo filtered, wnen It is not desirable to use, or convenient to obtain, suction from beneath. Probably the most useful application of thia air-current is to the blowpipe. With a Herapath lamp it is easy, by means of the stopcocks, to obtain a small oxidising or reducing llame suitable for chemical experiments, or the strong aud powerful jet for glass-blowing aud crucible operations. The author had not tried the apparatus with a Griffin's blast gasburucr; but, from calculations made, he had no donbt that, with a Herapath's lamp, he could get a blast quite as strong as that obtained by using the Griffin lump. H« stated that it would be desirable to have a float-valve at the mouth of the alrplpe, in the accumulator, to prevent the access of water into it, in the event of the apparatus at any time becoming deranged or over-taxed. In conclusion, the author explained how the apparatus might be used for delivering a steady current of any other jvas not very soluble in water. The cost of Mr. Patterson's apparatus, as fitted In connection with a Bunsen pump, is about 30s.

ANSWERS TO CORRESPONDENTS.

'•* All communications should be addressed to the Editor of the EnoLibit Mechanic, 31f Tavistockstreet, Covent Garden, W.C.

GEO. RYLAND, BIRMINGHAM.

On the 1st of April last wt considered it writ doirn iu our duty to dution the public against a Mr. Howard Rylanil, of Birmingham, by printing the following letter :—

"Borough of Birmingham Police Office, 1st February, 1970. "Sia,—Sergeant Jenni reports that Ii. Ryland has an office at High-street, Birmingham, but has not been there for six weeks. The last time we heard from him was from Hereford. His letters are called for by his father. There it no doubt hut (hat they are tvindlers.—Yonrs truly,

"G. Glosso*, Chf. Supt., J.A., C.C. ^ "Mr. ."

As the father of Howard Ryland naturally feels aggrieved at being called a swindler, and as we had no intention whatever of so designating him, we beg to express our sorrow for having accidentally mixed up his name in the caution we gave to the public. We therefore unhesitatingly offer our apologies ta him and to the public for any pain we may hare given him, or for nny injury he may have sustained by our iaadrertently unking big name with the statement made by the Birmingham police authorities. We therefore cheerfully withdraw all imputations affectiug his character.

ENGLISH MECHANIC MUTUAL IMPROVEMENT SOCIETIES.

It will be seen by advertisements on our front pag? , th.it two meetings, one in Manchester, and the other in Edinburgh, are called for Friday, the 29th, to consider the propriety of establishing English MechaNic Mutual lmprovemout Societies. If anything wero wanted to show the wide-reaching circulation and influence of this publication, it might be seen in this movement. In our opening address, at the commencement of the present volume, we stated that onr subscribers and correspondents were in one sense members of a national mutual improvement society; whereupon Mr. D. W. Kemp, of Leith, and Mr. A. TolhalSbn, of Manchester, simultaneously, without any concert with each other or communication from us, cill meeting*, at their own expense, of our subscribers iu Edinburgh and Manchester, to embody in practice a suggestion mado by one of our correspondents It is only natural that we should regard with interest thc-e initiatory meetings, and at the same time express an ardent hope that they may i*sue in Buccess.

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S. Kent.—Can't your friend, being at Reading, inquire about tbe School of Art there for himself?

J. H.chambers asks Us whether the character of a man may be traced in his handwriting. No doubt a man's character is exhibited more or lees in everything he says or does, and pnrticularly in the manner in which lie speaks or dresses. A fop or a swell may be seen in the way in which lie adjusts his hat or twists his moustaches. We never knew a man, for instance, with anything worth having in his head who wore his hat cm one side. We don't pretend to decipher 3. H. C.'s character in his writings if we ventured an opinion we should say that he was somewhat pedantic and precise, and that he paid more attention to the maimer of saying a thing than to the matter it might contain.

W. Ayton (Sydney, N. S. Wales) has sent us four threepenny pieces for four numbers of the ENGLISH Mechanic, out of which we have had to pay 6d. W. Aytou is probably not aware that the Post Office has authority to register a letter which " unquestionably contains coin," nnd to compel the receiver to pay the duuble fee, in the same way that an unstamped letter is charged double.

RappA.—Consult your dignity, and discontinue the correspondence. The insertion of your letter would most likely elicit a vulgar retort. In ability, education, manners, and antecedents, this foeman is altogether unworthy of your steel. Some men— fortunately only a few—prefer notoriety to obscurity, and the one in question would no doubt like to advertise himBelf in holding a controversy with you.

"Science for the Young."—Fourth portion next week.

"What Stripea the Sunbeam, * by "F.R.A.S.," next week.

J. R. T.—A series of articles on Levelling, which proves the rotundity of the earth, has just appeared in the Building News.

O. H. S.—The scientific paper referred to may have the use of the blocks.

The Sixpenny Sale Column is the only place in which can appear queries sent by Fireclay, One who Wants a Tricycle. W. Jones (Barnstaple), T. Thorpe, A Yurkite, S within.

THE ENGLISH MECHANIC LIFE-BOAT
FUND

Subscriptions to be forwarded to the Editor,at 3I,Tavistockstrcet, Covent-garden, W.C.

[table]

THE IMMTOR.

1097 G. Spencer, 77. Cannon-street. London, patterns on the* suriace of kamptuhcon or other similar substances

1008 W. Simpson and A. Gardner, llford, tinpruvtirn^m* la tbe construction of engines

low R. J. Everett, West Ham, utilising- waste products from gasworks

1100 A. V. Newton. 66. Chancery-lane. improvements in tlio production of metallic-alloy■ or manganese.—Acoinmnmeatinft

1101 W. R. Lake, Southampton-buildings, improvements u» knittlug machines

1103 A. A. Wibaux. Paris, engraving on glass, metals, wood, and other substances

1KB i*. N. J, Macabtes, Paris, water-teeding apparatus fur boilers

lift* W. R. Lake. Southampton-building, drilling or boiin^ rocks.—A communication

HOB W.Cotton. Loughborough. Improvements in the maiufaoture or looped or knitted fabrics

1106 C. Beard, Bury St. Edmunds, construction of partitions-of walls

1107 B. T>e I a Rue. Crnnfonl,improvements in croquet mallets

1108 E. P. Sheldon. Carlisle, improvements in water meters),. and in apparatus for boring cylinders

1109 H. Brooks. 81, Cumberland-market, Ue^cnt's-park. receptacles for containing liquids

1110 T. White, Birmingham, covers for dishes and plates

1111 1. Baggs, High Bolborn, Improvements in making white lead

1U9 T. Dlcklns, Midd'eton, machinery for spinning, talsiing^ doubling, and throwing silk

1113 A. Rorgnet. Swansea, construction of retorts, muffle*, pots, nnd furunces

1114 H. E. Newton. 66, Chancery -lane, apparatus tn be employed in the performance of gymnastic exercises.—A comirmnicatlon

1116 J. Craven. Wakefield, apparatus for raising and lowering heavy hud lea

1116 T. Wood, Manchester, omnibuses and anpamtus for indicating the number of passengers entering therein

1117 N. Murphy, Norwood, Ireland, securing more effectually the duty upon spirits in distilleries

HIS A. L. Dowie, Glasgow, improvements in treating copper, zinc, tin, and their compounds

1119 P. J. X. Gunthewnnd J. A. G De Latouche, Paris, revolvers

1120 J. L. Norton, Belle Sauvage Yard. Ludgate-hill, dressing and farrowing millstones

1121 W. H. Delamare. Deptford, machinery for treating cotton seeds

MM J. Barrow. West Gorton, treatment of napthalene, and of hydrocarbon bodies containing napthalene.

] Its P. Toepler, Graeechurch-street, cleaning wool

1134 J. Townsend, tdasgow.applyingheat In various chemica operations

1123 A. M. Strathern,Coatbridge.and XX G. Morrison,Glasgow safety apparatus for steam boilers

1126 W. P. Murray aad T. D. McParlane, Glasgow, apparatus* for shaping plastic materials

R. W. Wilson.—The numbers can be forwarded on receipt of

24 stamps.

J. W. P. Edwards—The charge is the same for any number of insertions in the Sixpenny Sale Column.

Ennuye.—There is no such paper. It is, as you observe, to be regretted that the greater number of the weekly journals give so much space to records of crime. Of course they profesv to only give them as intelligence, and not with the direct view of pandering to the low passions of their readers.

T. H. S.—See recent back numbers.

Henry Allen, Or Robert Cossens.—We did mt receive the stamps.

A Frtend To Tmtrovtmtnt.—Wc on give you no information. The English Government are not at present likely to take in hand any invention for the prevention of railway accidents.

A Smokir.—Answered recently.

Rabbit.—Scarcely within the range of a scientific journal.

Electro.—Described frequently in back numbers.

Contributor.—Yes there has; but don't waste your money

on such trash,

J. W. Pcrdue.—Your questions should be put to a respectable London patent agent, who would answer them properly at a moderate cost. Ton cannot expect us to do so. Write to lome of those who advertise in our columns for one of their handbooks.

H. James.—Wc cannot.

Caloric—There are such stoves. We noticed and illustrated one a few weeks back.

Wilfrid Hodgson.—Your idea is old.

Gkorgt. Freeman.—We cannot advise you. There are just
now too many patentees of velocipedes seeking the assist-
ance of capitalists.

A Constant Reader, (Thurgoland )— You are unreasonable.
Your query was inserted as early as possible, page 119.
The last remark in your present letter is uncalled far.

G. B. A. M.—Yes, during certain hours.

B. J. Williams.—The new newspaper postage regulations do not eome into operation this vear. Your query can only appear in the Sixpenny Sale Column.

W. Barber.—If you read our answers you would have seen that we did reply to you. Your query can only appear in the Sixpenny Sale Column.

George Bates—We do not see why you could not have given the informatiou. Your present reply is somewhat of an advertisement.

F. R. Smith.—" PrieDieu" wished to know where he could
get the designs.

R. Woodward.—Send a letter embodying a description of
Titanic steel, and we will insert it.

W. H. L. thinks Mr. Proctor "is too hard on poor Mr.
Beardsley, and that it would be better if Mr. P. would argue
with his opponent instead of abusing him." W. H. L.
should remember that Mr. Proctor has recently written an
elaborate series of articles on the earth in this publication.

Marine Bicycle.—G. Edwards.—Your drawing is not good enough for the engraver, and your description is not

clear.

The Sender or The Brick—You are mortified at your nonsuccess, and ashamed to state your name.

J. B.—We do not insert quack advertisements.

J. H.— Your reply is purely an advertisement.

F. F. C. suggests that Mr. Beardsley should less frequently use the terms "absnrd, erroneous, and impossible as applied to theories received by our greatest and wisest of men."

D. Hitch.—No stamps enclosed.

J. Wiqqinton.—We do not answer by post.

A Constant Reader says he sent a query which has not been inserted, and he supposes it was because the sender did not write well, or because he could not put F.R.A.S. to his name. Probably the query did not come to hand, or some notice would have been taken of it, however humble tbe writer might have been. We assure "Constant Reader1' that no partiality is shown to correspondents. If a peasant sent to us a suitable query it would be inserted, and if a peer sent us an unsuitable one it would be unceremoniously dropped into tbe waste basket.

J. H, R.—The qutry appeared a fortnight since.

Ih obedience to the suggestions of a number of readers, we have decided on appropriating a portion of our apace to a condensed list of patents as nearly as possible up to the date of our Issue.

1127 T. Mclsaac, Putnev. folding bed table

1128 W.Spencc, 8. Quality-court, Chancery-lone, manufacture* of hats

1129 G. C. Cooke, Woodford, apparatus for scoring or record* Ing numbers

All persons having an Interest in opposing any one of sueh> applications are at liberty to leave particulars iu writing ur their objections U> such application at the ulllce vf the Commissioners before the nth of April, 1870.

APPLICATIONS FOR LETTERS PATENT DURING THB
WEEK ENDING APRIL 19, 1870.

1063 C. H. Newman, Brentrord End. Brentford, producing
an unfermenting and untntoxicating malt liquor

1088 R. Wilson. 1'atrlcroft, near Manchester, Improvements in steam and other elastic fluid engines

1064 O. C. Walker and W. T. Walker, Midland Iron Works, Donnington, centre valves for gas purifiers and other apparatus

1065 T. Turner, 204, West George-street, Glasgow, bricks or blocks

1066 W. B. Halgh, Oldham, Improvements in vertical saw frames

1067 L. W. Thomas, Driver, Improvements applicable to fireplaces, stoves, and grates

1068 1. Adams, Boston. Massachusetts, treatmo t of metal surfaces coated by electro deposition with nickel

1069 J. Kirk, S. Shelmerdlne, and O. Froggatt, Stockport, apparatus Tor felting or "planking" the bodies of hats

1070 J. H. Johnson. 47. Lincoln's-inn-flelds, improvements in structures for the preservation of fruits.—A communication

1071 J. Howard, Bedford, improvements In ploughs

1072 M. Henry, 68. Fleet-street, improvements In telegraphic apparatus.—A, communication

1073 W. Lake, Souihampton-buildingB, London, improvements In brakes and starting apparatus for railway carriages. —A communication.

1074 W. R. Lake, Southampton-buildings, improvements iu whiffle-treea.—A communication

in". W. S. Coon. Rochester, New York, applying power to the running of machinery and tools, whereby such machinery or tools may be adjusted to any desired angle iu use.

1070 G. A J. Schott. Bradford, manufacture of yarns or threads

1077 B. Bangh and B. Walters, Birmingham, door knobs

1078 E. Lord, Todmorden, cleaning, preparing, and spinning cotton substances

1079 E. Weare, Rtonehouse, using the waste throads of condensing carding engines

1080 W, Angus, Fraserburgh, mast-head and other hoisting blocks

1081 M. Bailey. Islington, and W. J. Almond. Cheapslde, apparatus for spinning, doubling, and throwing silk, cotton, Ac.

1082 C. Joseph, south-place, Kenniugtan-park, improvements In filters.—A communication.

1083 W. Spence. 8, Quality-court, maohines for shaping staves for casks and barrels.—A communication.

1054 A. V. Newton, «d. Chanoery-lane, improved means for working railroad switohes.—A comniuuioati jn,

1086 0. Hamilton, Stratford. Improvements in bedsteads, whereby they may be rendered available as an escape lu case of flre.

1086 R. Marchant, Torrington-square, perpetual motion

1687 J. Pblllpson, Newcastle-upon-Tyne, Improving the windows of carriages

1088 F. W. Brooksbank. Nottingham, twist lace machines

1089 W. R. Lake, Southampton-buildings, an Improved mode of utilising cotton waste.—A coinmuuicatiou.

1090— F. Pattlsoo, Glasgow, a new or Improved metalfouuder's blacking

1001 T. Dale, Kingston upon-Hull. apparatus for extinguishing tires

1092 A. Taylor, Lydbury, Improvements la guns and projectiles

10M w. R. Lake. Southampton-buildings, Improvements In looms for weaving.—A communication.

1094 J. Plaakltt, Lincoln's-inn, Improvements in velocipedes. —A communication.

1005 L. Stewart, Edinburgh, improvements in wheels

1096 W. Jesty, Gosport, improvements in compositions for coaling ships

PATENTS SEALED.

3024 J. Raper. improvements in looms Cor wearfng

3031 J. Bottomley and W. tiottomley, fulling or milling:

woollen and other woven or felted fabrics
8037 M. Ker, improvements in curtains
soil W. Lake, improved nut for screw bolts
3044 A. Forder. velocipedes

S047 A. Clegg. improvements in sewing machines
3049 F. It. V. mdow, producing photographs tn pigments
SOW A. Munro, cutlery, edge toots, agricultural and other

implements
80M B. Salman, stamping and cancelling prf>?s
S058 A. Brady, improvements in purifying iron or any other

metal.—A communication

3064 H. Brooks, metallic cap or cover to glass or other bottle* or vessels

3065 J. Wcckor, apparatus for stopping njuies

S067 W. R. Lake. Improvements iu rotary blowing engines.— A communication 3091 P. Walker, apparatus for rendering coal mines less

3116 O. L. Hopson, apparatus for reducing the diameter of wire or rods for wire drawing 3160 C. Sacre, Improvements in the manufacture of wrought

3200 C. De Vltle Wells, Improvements for regulating the

■peed of marine steam engines
3256 W. Harrln. locks and latches
.;■',"- J. Woodward, liquid meters

8509 J. P. Kent, mortising, tenoning, and sawing machine
3593 P. Kooh, manufacturing untapped nuts intended lor

sorew bolts
1011 K. Pilling, looms for weaving

1013 J. Petrie. washing wools auo other fibrous materials
1015 J, M. Kliner, apparatus for laying submarine telegraph

cables . ,

3056 W. Hey wood, improvements in carriages
3066 G. M. Ashforth, applying motive power applicable to.

working sewing machines _

3U73 R J. Goodbody and R, E. Donovan, apparatus Tor

roasting tobacco for snuff , ,

3074 T. Gibb and O. Gelstharp, furnaces for calcining ores
3076 J. R. Grayson, apparatus forelipplng or shearing homos
3084 R*f.coUand W. Motvor, sulphuric acid residues utilised

and employed for the production of sulphate of soda
3087 T. Hydes, J. Hennett, and J. li. Bennett,propelling ships
8101 T. Hoey, improvements in fire places
3102 D. Spill, preparation and use oi solvents or xyinfmne
3108 T. Dunn, improvements in locomotive steam englues,
8123 J. Watson, improvements in presses for compressing

cotton , ,,

3134 A. Knowlea, apparatus for cutting and getting coal
8144 J. H. Spencer, compound tor lubricating the Journals or

necks and bearings »r rolls, rotating shafts, and other rotating

3189 N. W. Blanchard, substitute for curled hair for upholstering and other purposes

3190 8. Husk, shoes for horses and other animals.—A communication

3249 I. Nascb, button-hole sewing machines

3287 P- Koch, fastening the knobs or handles of locks.—A

communication
3305 c\ Ashhury, improvements In steam boilers
s»i5 T. Weston aud H. Weston, manufacture and coating or

casing of metallic tubes and rods
,%S2 G. T. Livesey, apparatus used in the manufacture or gas
8717 J. B. Gough, improved collar stud ,

14 J. Smith, sickles and wires oounected with mulM for
nning
298 D. Robertson. Improvements in cardini engines

858 J. Ward and .1. Bowing, preparing and drying yeast

859 H. Hond and J. Kiley. manufacture or quilts, counterpanes, s>nd table or toilet covers

483 S. W. Clark and W. R. Sykes, signal and other lamps 505 S. Hulme. removing patnt from wood 512 W. B. Adams, railways, tramways, common roads,ana machines and vehicles to run theieuu 5/8 A. Godillot, au Improved military ter.t. 509 L. atenic, construction ofwheei tlnsn

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WHA.T STK1PES THE SUNBEAM.

By A Fellow Op The Royal Astronomical

Society.

THERE aro, probably, very few modern discoveries which have excited such widely-spread interest as that of what has been called Spectrum Analysis; in fact, it Jb almost impossible to peruse, cvon in a desultory way, much of the current Scientific literature of the day without nieetin" with references, more or less explicit, to it. Inasmuch, however, as the subject has not hitherto been treated formally in our columns, and inasmuch, further, as it appears to us that a familiar exposition of it may enable many of our readers to appreciate and understand the references to which we have alluded, and which, presumably, have now little or no meaning for them; we have determined to endeavour to place the whole matter in as popular a^form as it is susceptible of explanation in, and to tell the marvellous tale of the detection of the chemical constitution of our great centre of life heat and light, the Hun (and even of thst of some of those infinitely distantbodies which spangle the midnight sky), by the aid of a mere triangular stalk of glass and a narrow slit in a metal plate.

We must, however, ask here, as we did on a former occasion, for the sustained attention of the reader. It is not a very easy subject which we have taken upon ourselves to discuss, and in our attempt to make it apprehensible we shall have to proceed, step by step, with, it may be, more or less iteration, in a predetermined sequence of explanation. We would, then, request the Student, on no account to proceed with any paragraph, after the first, nntil he has thoroughly mastered the preceding one. If he will try his best to comprehend ns, we will promise to use all our endeavours to be comprehensible; and to use only such language, and employ only such illustrations, as shall be within the grasp of any moderately-educated artificer who may be sufficiently interested in the subject to follow us.

It was in iho year 1675 that one of the greatest, if not the very greatest, of Englishmen who ever lived, Sir Isaac Newton, made the remarkable discovery that white light was not homogeneous; that is to say, that it could be split, or decomposed, into lights of various colours, and this he ascertained from the circumstance that when, under certain conditions, a ray of white light is refracted or bent, its components are bent in different proportions, or some more than others. He demonstrates this in Prop. 1., Theor. 1., of his "Opticks," published in the year just mentioned, under the heading, " Lights which differ in colour, differ also in degrees of refrangibility." Into his proof of this we need not enter, since we are now more immediately concerned with his second proposition, " The light of the Sun consists of rays differently refrangible." The an nexed figure(Fig. 1) copied from the "Opticks," will serve to exhibit the manner in which he shows the truth of this experimentally. Through a round hole P, of srd of an inch in diameter, Newton allowed the Sun to shine upon one face B C, of a triangular stalk of glass (which we call a prism), " whereby," ashesavg, "the beam of the Sun's light which came in at that hole might be refracted upwards towards the oppnsite wall of the chamber, and there form a coloured image of the Sun. The axis of the prism (that is the line passing through the middlo of the prism from one end of it to the other end, parallel to the edge of the refracting angle) was m this and the following experiments perpendicular to the incident rays." This means nothing more than that a sharp edge of the prism ZT,id0Tnward?' aad "'« »neh edge was parallel to the .hutter ;n which the hole was made, and to the floor of the room in which the experiment wag tried. Having found the position of minimum deviation of the prism (english Mechanic, Vol A., p. 620), he proceeds as foUows :-« The

[graphic]

prism, therefore, being placed in this posture, I let the refrncted light fall perpendicularly upon a sheet of white paper at the opposite wall of the chamber, and observed the figure and dimensions of the solar image formed on the paper by that light." He then goes on to describe the size and shape of this image of the Sun, and to prove that the different parts of it are differently refracted, and concludes his 2nd Theorem thus :—" This image or spectrum P T, was coloured, being red at its least refracted end T, and violet at its most refracted end P, and yellow, green, and blue in thd intermediate spaces, which agrees with the first proposition, that lights which differ in colour do also differ in refrangibility. The length of the image in'the foregoing experiments I measured from the faintest and outmost red at one end to the faintest and outmost blue at the other end, excepting only a little penumbra, whose breadth scarce exceeded a quarter of an inch, as was said above."

The experiment whose nature we have thus indicated is nt once so important and so striking when seen for the first time, that we would urge evory one of our readers to repeat it for himself. The triangular prisms dependent from candle "lustres "—not those cut into many facets, but the plain triangular stalks of glass—will answer excellently to exhibit the phenomena of which we have been speaking ; and as such a prism will be of groat nse in illustrating our future explanations, we would advise everyone who intends to follow' us through this es£ay to provide himself with one or more of them. They may be had for a few pence each.

We may add to what we have suid, that, by receiving the spectrum as described above, upon a screen, and then cutting a slit in that screen so as to let light all of one colour, say green,pass through in an isolated state, Newton found that such colour was no further decomposable, and that, on letting this ray fall^upon a second prism, ho only got green light upon another screen placed behind the first to receive it. He further showed that by examining the spectrum P T through a second prism placed below the level of the first, so ns to reverse the order of refraction, here-composed his coloured band into a spot of white light.

How or why this combination of colours affects the eye as white light, is too recondite a question to be diseased here, even were there any tenable theory to acconnt for it It is mainly connected with the anatomy and physiology of the eve itself, and it is therefore impossible, in this place, to do mors than refer to it. We may just say, though, that the | henomenon itself may be exhibited in another form by means of a rapidly-n fating disc uprn which the prismatic colours are panted in that due rj.-op-rt-.il, ani by the moli.ii -y. which

they are.blended, so that the disc affects the ey e as an nniformly white, or slightly greyish-white one. Brew6tcr (" Optics," pp. 7l| ('/. seq.) propounded the hypothesis that there were three distinct eolonred spectra—one red, the next yellow, and the third blue—which overlapped, the maxima of the red and blue spectra being at the ends, and that of the yellow in the middle of the visible spectrum, and the overlapping producing the intermediate fkades of orange, green, &c, &c. The fallacy of this hypothesis has, however, been since conclusively shown by HelmholU, who has proved that the green, for example, is not made up by the superposition of blue and yellow, and that it is nndecomposable, and of one definite refrangibility. The importance of the discovery that light of each specific degree of refrangibility is monochromatic, and that each ray has its own special colour, will be seen as we go on.

So far as we have gone, then, we have arrived at this result, that what we call white light is in reality a mixture of violet, indigo, bine, green, yellow, orange, and red lights, and that, after falling upon one face of a prism, a beam of Sunlight emerges from the adjacent face, spread out into a sheaf or fan of theso its component colours, the violet being the most bent, the indigo less, the blue less still, and so on to the red, which is bent the least of all. We have further learned ■ that each of these is legitimately a primary colour; that is to say, it is of a fixed and unalterable refrangibility in the same medium, and it is monochromatic, or whole-coloured, and, consequently, undecomposableinto any simpler elements. Should the reader, however, follow our advice, and repeat. Newton's experiment for himself, he will observe that the colours are not sharply defined at their junction with the adjacent ones, but that they melt, as it were, into each other, and that the spectrum is, in fact, a continuous one,without break or interruption. It will readily be seen that this is referable, inter alia, to the shape of the orifice through which the beam of sunlight is admitted, as it is pretty evident that the rays which come through are inclined to each other at the angle (about half a degree) subtended by the Sun's disc to the eye. How the use of a round hole in his shutter caused Newton just to miss a discovery of the most vital importance we shall now very soon proceed to exhibit.

Before doing so, however, it will be as well, at this stage, to glance at the physical properties of the variously-coloured constituents of the spectrum, remembering that all light is duo to the undulations of a medium pervading the whole of space, the difference in the rapidity of thu vibrations of this medium affecting the eye as differences of colour. Numerical details on this subjict may be found iu a lctlcr ut Jj. 33 .1 ill >':.3:Lt

volume With regard to the worls, "extremred " and "extreme violet," with which the table (I. a.) commences and concludes, we may just observe that, beyond the confines of tho ordinarily visible spectrum, exist rays of light both more and less refrangible than any of those which we commonly see; but that by certain artifices or contrivances these may be rendered perceptible. Commencing at the red end, we find that the greater part of the heating effects of the Sun's light are refornblo to those red rays, and delicate experiments have shown that the maximum heating power resides at a point beyond that at which red light, or any light, ceases to be visible to the eye. Sir William Herschel was the first to draw attention to the fact that heating power mainly resided at the red end of the spectrum, announcing his discovery at the very beginning of tho present century ; while as early as 1777, Scheelo published the results of some experiments, which showed that chloride of silver blackoned much more rapidly in th<» violet rays than in any other part of the spectrum. The preponderance of illuminating power in the yellow rays must have struck every one who ever viewed dispersed light at all. Summing up, then, we may say that the greatest heat resides in that part of the spectrum just outside of the visible red; the most energetic chomical power just within the visible limits of the violet, and the brightest light about the middle of the yellow.

But it is time to return to what we were saying as to the shape of the aperture through which the Sunbeam is admitted to fall upon the prism; and we may now proceed to see how Wollaston made (without knowing it> a discovery of very high importance in connection with the subject which we are now considering. Instead of employing, like Newton, n round hole in his window-shutter, through which a number of overlapping spectra find their way, he let the Sun's light pass through H narrow slit parallel to the refracting edge of the prism, and upon now examining the spectrum he found it no longer continuous, but crossed in several places with fixed dark lines, which wero permanent. Wollaston, however, like many other discoverers, seems to have quite failed to see the importance of what he had found out, and the matter slumbore 1 until the year 1814, when the great German optician, Frannhofcr, took the mattor up. and, by viewing the spectrum of a very narrow slit through a telescope, succeeded in mapping, we believe, nearly 5M0 of these lines. They are hence called " Fraunbbfer's lines," even to this day. He further found out that these lines existed in both direct and reflected sunlight: that moonlight and the light of Venus also showed them, and - that in the spectrum obtained from each of these sources, the position of the visible dark lines was fixed and invariable. Fraunbbfer made another discovery, too, of very great importance, which was that the fixed stars (which it is well known are themselves Suns) gave spectra containing dark lines, but they were not the same tlark linen as he had previously detected in the Sun's light, whether directly or indirectly derived from him.

For the better explanation of our subject, we will now dismiss temporarily from our consideration the spectra of the celestial bodies, and confine ourselves for the present to the effect of heat on terrestrial ones, in so far as such heat leads to the evolution of light Fvery blaoksmith knows that when an iron rod is put into the fire it first arrives at a red heat, and as it becomes hotter it gradually emits light of greater and greater refrangibility, until ultimately it ends by giving off rays of all degrees of refrangibility, or becomes, as they say, white hot. If the reader will watch the gradual heating of a common poker by the aid of ouo of the prisms which we have recommended him to procure, he will find that it will begin by the emission of red rays; that as the heat increases, its spectrum will lengthen; and that orange, yellow, green, blue, indigo, and violet light will in succession become visible, the whole of tbo prismatic oolours becoming apparent when the poker is intensely white hot. The same sequence of phenomena will be exhibited by any body, solid or liquid, which can be sufficiently heated; and it is most important to remark, that in each and every case (with the solitary and animportant exception of an extremely rare sub

incandescent gas, what sort of light will that emit?
The answer to this is a curious one. Every element
in a gaseous state, when heated until it becomes
luminous, gives off its own special and peculiar
spectrum; but this, instead of being continuous,
as in the case of that emanating from a solid or a
liquid, is broken, or discontinu ras, and consists of
bright bands or lines, with dark spaces between
them. A simple and very striking way of showing
this is by the aid of R common spirit lamp, into
the flams of which certain salts are introduced to
volatilise and burn in the form of vapour. Makers
of fireworks are familiar with the use of strontium
to produce a red colour, and of barytes to afford a
green one; and we have, most of us, tried the ex-
periment of burning a mixture of spirits of wine,
and common salt in a darkened room for the sake
of observing the ghastly effect produced on the
countenances of the spectators by its monochro-
matic yellow light. Now it is of the utmost im-
portance to observe here, that all the salts of
sodium (the base of common salt) tinge a flania
yellow; all the salts of barium, green; all the salts
of strontium, red, and so on: and further, that if
we can, no matter how, heat the vapour of any
chemical element sufficiently high to render it lumi-
nous, we shall find that its spectrum is special to
itself, and dissimilar to that of any other body, and
all this irrespective of the ordinary condition of
such element, be that solid, liquid, orgaseous. But
that we ore, for obvious reasons, denied the use of
enrornatior printing, we should have certainly
given figures of the spectra of some of the alka-
lies as well as of those of carbon, hydrogen, aud
nitrogen; but under existing circumstances we
must forego this valuable aid to explanation.

Prior to entering into any detail as to the kinds
of spectra which we obtain when we regard the in-
candescent vapours of the various bodies to which
we have been alluding, it seems essential hero
that we should make some reference to the method
in which these spectra may be observed, and we,
therefore, to render this more intelligible, here
(Figs. 2 and 3) give a figure of oneof the simplest
forms of spectroscope, the pattern being one of
those of that very able and eminent optician, and
well-known amateur observer, Mr. John Brown-
ing, F.R.A.S., to whom, probably, this instrument
owes more than to any one artist living.

It consists, in effect, of a very dense flint
glass prism P, standing in it truly perpen-
dicular position in tho centre of the circle C, which
is itself supported by the stand S. Th,o circle
C is gradnatcd, and upon it is an upright ring F,
fixed firmly, another ring M, attached to an index
I (reading by means of a vernier V), moves round
the circle C on such index. Into this latter or
moveable ring a telescope, M T, of the ordinary
construction, is screwed. Into the fixed ring is
fastened another telescope, with its object- glass
also directed towards the prism, but, in pr ice of an
eyepiece, carrying in its focus an arrangement of
"knife-odges," shown infrontviewof Fig.3. This
consists of two thin plates of metal s s, with their
inner edges carefully ground and accurately
parallel, and these are made to approach to or
recede from one another by means of the screw
with a milled head a, the effect of this being to
make an exceedingly cban sharp slit of any width
that may be required; a part of this slit is covered
by the reflecting prism p, by means of which the
light from any source placed in the position of
the candle C, is reflected through it, together
with that passing directly between its jaws; so
that the spectra, side by side, can be seen in the
field at the same time, and the comparison insti-
tuted between them. It is only needful to say at
this stage that the slit formed by the knife-edges
i sturnedtowards the light whose spectrum is tc be
examined; that of course the rays pass ont of tho
object glass F parallel, fall upon one face of the
prism P, are refracted and dispersed by it, and
that then they enter the object-glass M, and the
spectrum is observed through the telescope T M,
to which the object-glass belongs.

Let us conceive, then, that, this instrument
being in adjustment, we turn the slit towards
a burning spirit-lamp, into the flame of which we
will commence by imagining that sodium, s ly in
the form of common salt, has been introduced;
and let us proceed to see what sort of a spectrum
this yields. Cortainly a most remarkable one;
i a brilliant yellow band, and that is all. The light

spectrum of potassium, what a wonderful cjntrust does it present! Two narrow lines at the red end of the spectrum, separated by a dark interval then a huge dark gap, involving the orange, yellow, green, blue, indigo, and beginning of the violet, and then one%olitary band in the violet— serve to indicate that the burning vapour of potassium emits lights of practically only two degrees of refrangibility, and those at opposite ends of the spectrum. If we regard the spectrum of strontium, wo find, as we might expect, that the major part of its light is in the red and orange— where seven bands may be counted without much difficulty; then comes a wide black gap, and anon we find a solitary stripe of blue. We have given these throe elements as examples, but had we extended them to thirty, our story would have been the same. Each and every one would be found to differ from all the rest, and to possess its own proper system of bright lines, some at one end of the spectrum, some at the other, some consisting of rays of several degrees of refrangibility, but all being composed, without exception, of bright bands with uumistakeable dark gaps between them. We may just mention, incidentally, that so astoundiugly and inconceivably delicate is this

1

method of analysis that the ths of

180000000 grain of soda has sufficed to show the sodium spectrum, and to flash up in the instrument as a brilliant yellow streak!!l; and further, although it is of little importance to our present object, that this line of sodium, when examined with adequate, optical aid (of which more by-and-byo), is seen really to consist of two lines, like hairs, close together. We may perhaps also add, that we may have as many substances ia B vaporous form as we please at the same time in one dune, and that as they successively become volatilised, their spectra will appear one after another when that fl ime is examined by the aid »t the spectroscope, ultimately remaining simultaneously visible until the dissipation of the respective substances which produce them.

(To be continued.)

stance called Erbia which we may quite neglect \ emanating from this element in its vaporous form here) the spectra of all incandescent solids and is wholly of one degree of refrangibility. Not a liquids whatever, are continuous—that is to say;! vestige of green or orange, and, d fortiori, not of uninterrupted and uncrossed by dark lines of j blue, violet, nor red—a single bar limited in its any sort or description. But suppose that, instead width by that of the slit, and we have the entire of n solid or liquid body, we are dealing with an [ spectrum of sodium. If now we examine the

ELECTRICITY—ITS THEORY, SOURCES
AND APPLICATION.
Br J. T. Spbague*
CContinued from page 75.)

THE simplest form of galvanic generator, and
the one first devised, is the combination o
alternate plates of copper and zinc ; most elec-
trical works employ a good deal of space, and
many figures, in describing the various form* de-
vised by way of improvement, by Cruikshank,
Wollaston, and others, consisting chiefly of the
mode of arrangement in the containing vessels,
the use of double copper-plates surrounding the
zinc, and snch-liko matters, the value of which
has been entirely destroyed by further progress.
But as the simple copper-ziuc arrangement is the
most unsatisfactory form known, it is simply
wasting time and space to describe such modifica-
tions of it, and therefore I shall only refer to it
when required for elucidating principles, and as
the starting point of all the forms.

109. Exciting Solutions —A current may be generated by two metals in many solutions, but for tho single liquid cell the only practical reagent is sulphuric acid. This is the most powerful, and the cheapest, as it may be bought as commercial oil of vitriol, from about five farthings a pound, and still lower in large quantities. I may as well say here that for the convenience and information of readers I shall thus name the price of all the articles employed; those prices will bo thoso I pay myself, knowing where to go, and are ordinary fair retail, not wholesale or trade prices; at the same time, ordinary purchasers in small quantities, and particularly buyers at chemists, as the retail dealers in drugs are' called, will be asked much more.

Ordin irv rectified oil of vitriol of full strength, specific gravity about 1M0, will serve, but ordinary brown vitriol should be avoided for tin) reasons; if it contains nitrous acid it would b» injurious to tho silver in a Smee'e cell, and cans* local action on the zin *, in spite of amalgamation, in all; to test for this, mix a few drops with water in a test tube, and drop in a crystal of pure) ferrous sulphate, or green vitriol, if «r the af'-l has cooled; if a brown colouration is produced, reject the acid. Another very common impurity

is arsenic, which would be given off with the hydrogen and form a most deadly poison, if much is breathed, and be unwholesome in any case. Sulphuretted hydrogen passed into the diluted acid will cause a yellow precipitate if there is arsenic present. These are the only impurities of any consequence.

A good solution is made by mixing 1 part by bulk wjjji 10 «f water, which should be soft, as water eontainijKg lime is apt to form a deposit on the metal surfaces ', if no other is accessible, it should be boiled with a little carbonate of soda and allowed to cool and settle before use; 100 grains hy measure of such a solution will dissolvo about 11} grains of commercial zinc, but it is bad economy to nearly saturate the acid, particularly if several cells are combined in series, aa zinc is then pretty sure to be deposited on the lower part of the negative plate, which is thus destroyed for the time, and from which, as the sine is pure, it is a troublesome process to dissolve it again. But allowing for impurity in zinc, local action, and a due proportion, or about one-fifth of free acid left, one pint of this solution would dissolve about ijoz. of zinc. We may thus calculate the work any cell is capable of doing as about equal for each pint of solution to 24 equivalents of chemical action, this being the true electrical nnit of "quantity," as I shall hereafter explain. The cost of generation for each unit would thus be that of one pint of solution, ljoz. of zinc, and a fair per centage for wear of negative plate and vessels, divided by 24. This is the acid, and these the conditions applicable to all -the following forms of simple cell.

110. Coppks AND Zinc.—When -first a pair of plates are immersed in dilute sulphuric acid, and the wires connected to a galvanometer, a considerable deflection is produced, marking a powerful current, but even in a few minutes tho effect rapidly decreases. The following experiment was made for purposes of comparison, with plates 2in. by1,lin., half an inch apart, in the above-described solution, the plates perfectly fresh, the copper having been washed in nitric acid, and then in several waters; the deflections are those of a Tangent Galvanometer, and therefore capable of comparison, and, as will bo hereafter explained, of actual valuation. First deflection, 40", alter successive intervals of five minutes, 34, 33, 32, 31, 31, 30, after one hour, 28, and after an hour and half, 26. The galvanometer and connections consist of obout 15ft. of No 13 copper wire, a resistance by actual measurement of '031, or l-32nd of a British unit.

After a short while the copper I'b seen to be covered by a dark film, whioh it is commonly stated is oxide of copper, and the other metals contained in it. This is erroneous however, for it is evident that oxides could not possibly form in the presence of nascent hydrogen; it is really a combination of this hydrogen with the metal, and the diminishing power of the cell is due to the formation of this hydride or alloy .which prevents contact of the copper with the liquid, thereby increasing the internal resistance, while the affinity of the hydrogen in this condensed condition for the aeid radical resists the polarising power of the zinc, and therefore diminishes the electromotive force of the couple or cell.

Pure copper, as deposited by the electrotype process, has a higher electro-motive power, probably because of its purity, but also on account of the nature of its surface, which is covered with innumerable fine points, from which the hydrogen is given off more readily than from a" smooth surface. Hence if a copper negative plate is to be used, it should have a deposit of copper formed on it. Such a plate gave the following comparative results:—First deflection, 50°, and in successive five minutes, 35, 34, 34, in one hour, 33. and one and a half, 32.

It will be noticed that the greatest loss of power is in the first few minutes; indeed, the fir>t deflection is of scarcely any value for the fall is so rapid that it is nearly impossible to say what the trne deflection is, or when the needle has reached its position of rest after the first oscillations.

111. Iron And Zinc—Iron has often been recommended as a positive element because its surface keeps clean; its volue will be evident from the following results, 25° falling to 18 and 1C in ten minutes. Still its cheapness may tempt some to use it, a very unwise economy. For this reason it should be stated that wronghtor rolled

iron is alone fit for use, as the presence of carbon in cast iron sets up local actionB. One reason why iron is unsuitable is its low conducting power, which adds to the internal resistance.

Lead gave a momentary deflection o£ 39°, which fell in a few minutes to ">.

112. Silver And Zinc. The silver in this case was better than rolled metal, as it was deposited on electrotype copper, thus giving a favourable surface; this answers perfectly well. If a thick plate is laid on, it gives of course a higher conducting power, and is obaaper, for even the two coatings will contain less silver than a silver sheet of such thickness as to bear practical treatment. It gave HO" falling ie 48, 47. 46, 45, at five minute intervals, and 4*° after one hour. Like copper, the surface is covered with a brown film, due to the condensation of hydrogen.

113. Platinised Silver.—Smee having assured himself that the nature of the surface was of the greatest importance, and that the hydrogen is more readily given off from a rough surface than a smooth one, and also bearing in mind that platinum has the highest electro motive force of all the metals as opposed to zinc, deposited this metal as a fine black powder on the surface of silver, thus attaining both those objects, and yet avoiding the expense of platinum, and also the low conductivity of this metal, and the battery thus arranged, and which justly bears his name, is one of the most valuable gifts ever made to electrical science. It is of simple construction, the silver sheet is held in a wooden frame in a saw-cut down the middle of the inside surfaces; the top and bottom bars may be Jin. thick, and the sides J, the wood being well baked and soaked in melted paraffin before putting together by the usual mortises and tenons, and afterwards well covered with sheila* varnish; a sheet of zinc is held on each face by means of a brass clamp with a screw, which presses them against the frame, and carries also the binding screw for the connection, that for the silver passing through a hole in the top bar, and being soldered to the silver; the zincB should be narrower than the silver, in order to give free escape for the gas.

Silver ready platinised may he bought, but it will require occasional renewal, and the process is very simple. The silver, being perfectly clean (it is best to wash it with nitric acid), is placed in a cell containing acid solution, and connected to it is a wire with a small piece of zinc attached, this may be merely wrapped in a piece of blotting paper, or a porous cell may be used to keep it out of reach of the platinum. The zinc is now dipped into the acid to a small extent, Jin. square is enough, so as to produce a very slight action, and then a drop or two of platinic chloride is added to the acid, and immediately it begins to be reduced on the silver; after this is found to be wholly coloured, tho action may be increased, and more platinic solution added, and at the last a brisk action should be prodnced, the object being, first to secure an adhesive deposit, and then a ipnlverulent one of platinum. The platinum solution is made by dissolving scraps of the metal in aqua regia, or a mixture of nitric and hydrochloric acid, by the aid of heat. Crystals may be obtained by evaporating to dryness and re-dissolving, but for the purpose required this is needless, as the excess of acid is not injurious.

Treating thus the plate used in the last experiment, and using with it one zinc, so as to have the same conditions as in all the other trials, it gave 71° ; at 5 minute intervals, 6G,fi3, 61, 59, 57, in an hour, 50, and in an hour and half, 46. Like all the others its power suffers a rapid decrease, in this case due, chiefly, to tho remarkable power possessed by spongy or pulverulent platinum, of condensing gases to many times its own volume, and retaining them in this condition. However, these comparative tests, though valuable and instructive, only treat one aspect of the question of value, that of constancy, and relative activity on short circuit; before coming to a conclusion, the action has also to be considered, when varying resistances, such as are met in practice, have to be overcome.

114. I have long been in the habit of using a peculiar plate in my Smee's, one composed of copper wire gauze, 40 meshes to the inch, which I first copper by electrotype, and then silver and platanise; the reason I used it at first was to enable the zinc to he placed in the middle, and to give a freer escape for the •ias, and although the surface is at first view diminished by the openings, it is not so really, as the whole of the surface of the wires is active, the back «b much as the front. Such n plate prepared forcompari son gave 69", falling to 50, 47, 45, 44, and in an

hour and holt, 42; this is less than the .solid plate, bnt tho reason is that it was not plate! sufficiently thickly, and consequently its surface was smaller than it should have been.

115. Cabbon And Zinc.—Mr. Walker suggested the use of graphite plates, and has used them in batteries for telegraphic purposes; this combination gave 25°, falling in an hour to 2:!, and in an hour and a half to 21. It thus appears that the force is lower than with silver, or even copper, probably on account of the lower conducting pewer of carbon, but, on the other hand, it has the merit of comparative constancy. v.^

It has also been platinised in the same manner as silver, which greatly increases its powers. A* on illustration of the great resistance produced by tbo hydrogen, I arranged the plate, during platinisation.in connection with the galvanometer, showing a current of C* ; the moment the platinum salt »'as added, and the hydrogen employed in reducing it, the deflection rose to 34°, falling again to 12 as gas began to be again given off. When arranged as in the other cases, it gave CS", falling t' (S3, 59, 55, 51, 49, to 37 in one hour, and 31 in an hour and half.

Saline Solutions.—As it is well to know what attempts fail, as well as what is successful, I may say that many saline solutionswill generate currents, but none are of any use in single flnid cells. Thus, carbon and zinc in common salt, chloride of ammonium, nitrate of soda, and various others gave a deflection of 6", rapidly falliug below the power of the Tangent Galvanometer ; in fact, the zinc is not able to displace the alkaline or earthy metals which are chemically employed to precipitate it. These solutions have important uses in double fluid batteries, but then other affinities come into play, and these salts act chiefly as conductors, and act on the zinc only by being themselves acted on by the other agents, as well as tho zinc.

117. Having examined the principal elements employed in batteries whichsetthe hydrogen free, their construction is a mattor which need not occupy much attention, for the plan described for the Sraec is applicable to all, bnt without requiring a complete frame; the old fashion of cementing plates into troughs is entirely abandoned, because it is impossible to ch an them, a process constantly required, as the copper, when used, needs to be frequently heated to redness to renew its surface, and the zincs ought to be well brushed and freshly touched with mercury after 21 hours' full action, or they lose power, and become subject to excessive local action; but if this care be taken the local action is very small, and it is hardly necessary to remove the plates when not in use, unless a long interval is likely to elapse before they are to be used again, ns they keep in much better order in the acid. Various experiments have resulted in a loss of from a quarter to half a grain per square inch of surface iu 24 hours, in solutions of fall strength.

118. Before passing, however, to the compound forms, I will make a present to the readers of tho English Mechanic of a cell of my own arrangement, based on the long series of experiments I have made, and of which the foregoing are a selection. I should have deferred its description till after the examination of the general principles, but 60 many inquiries have boen made lately on this subject that I expect the description will be welcome.

The containing vessel is an ordinary stone jniabout Sin. wide by 9in. de>ip; a strip of gauze loin, by 5in. is treated as before described, bnt a copper plate silvered, or sheet silver would do, though I believe not so well j this is made into a cylinder fitting inside thejar, and slung by three copper hands or wires (soldered to it nnd covered with cement or gutta percha after completion) so as to leave a space of Sin. in the jar below it ; the suspending wires are turned over to the outside and soldered to a band going round the jar and fitted with a binding screw, a wooden cover U fitted with a hole in the middle, through which passes the connection to the zinc. The zinc is a strip 2in. wide by }in. thick, and at its foot is secured a little shoe or saucer of gntta percha containing mercury, which maintains the amalgamation. Of course the negative element is somewhat expensive nt first start, but the object is to give it as large surface as possible; a series of carbon plates might be substituted, but they would cost as mnch as the silver nnd have no residuary value, and give loss force ; the platinising is done at the first charging, taking care to reduce all the platinum before inserting the proper zinc.

This battery is nearly constant, it deflected my

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