1845.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



S7 



sponsible officers of both cstablislmienls. They arc then delivered to the 

 Master's assay-master for analysis. Prof. Brande here explained that, for 

 the purposes of circulation, it was necessary tliat gold and silver coin should 

 be milted with an inferior metal in certain accurate proportions. This alloy, 

 as it is called, is, in the case of gold, usually a mixture of copper and silver 

 in equal proportions — but it is essential that the copper thus used should be 

 perfectly pure. In the gold coin of this country, eleven parts of pure metal 

 are combined with one part of alloy, while in the silver coin 4rr of alloy arc 

 considered sutticient for 11 jij parts of silver. The French standard is the 

 same for both metals— viz. 9 metal and 1 alloy. Having thus been rendered 

 less flexible, and more available for the purposes of coining, the ingot of 

 gold is melted iu a black-lead crucible; during this process it is carefully 

 stirred by a black-lead rod to insure the equal ditfusion of the alloy through- 

 out the mass. \\ ere this precaution neglected, the quality of the bar into 

 which it i« cast would not be uniform. And it is obvious that a scarcely 

 appreciable variation in this respect might seriously deteriorate tlie value of 

 coin. The same process is adopted in regard to silver, excepting that Mr. 

 Morison has advantageously adopted cast iron, instead of black-lead, as the 

 material of the melting-pot for this metal. Prof. Brande liere noticeil one 

 of the discoveries of Dr. WoUaston as having a most important bearing on 

 the chemical operations of the Mint. By rendering platinum malleable, and 

 thus convertible into crucibles and retorts. Dr. WoUaston not only provided 

 means for manufacturing sulphuric acid at a cheaper rate, but enabled that 

 substance to be readily used in extracting silver from ingots of gold. Tin' 

 Refiner extracts, at a small cost, the silver which generally accompanies 

 masses of gold. And, as no seignorage is charged on coining, and as he is 

 entitled to coined in exchange for uncoined gold, without expense, whatever 

 silver he can remove from his ingot is so much clear gain to him. The bar 

 of gold is now consigned to the ancient company of Moneyers, and here the 

 mechanical operations, which convert it into coin, commence. These, how- 

 ever, are necessarily controlled by chemical principles. When broken down, 

 as it is called, {i.e. squeezed to the thickness of the coin), the bar is annealed, 

 (heated, that the metal may become tractable,) but heated out of contact 

 with air, lest the alloy should burn. Prof. Brande described, and illustrated 

 by models, the operations of the rolling-room : the extremely accurate uni- 

 formity in the thickness of the ribband of gold, from whence the blanks are 

 struck, obtained by Sir J. Barton's machine. He then showed how, by 

 means of most delicate adjustments, any minute variation in the quality of 

 different parts of the ribband was compensated in the blank-cutting machine. 

 He explained Mr. Bolton's contrivance for making the atmospheric pressure 

 the moving-power in this powerful, yet most accurate engine ; and proceeded 

 to describe how, after being again annealed, the blanks are stamped and 

 milled. Prof. Brande briefly noticed what are called the trials of the pix ; 

 i e. the examinations into the quality and purity of the bullion before it is 

 received by the Moneyers, and when, having been coined by them, it is about 

 to be issued to the public. These examinations are always strictly private. 

 The result, however, is sufliciently and most creditably notorious — the ac- 

 knowledged purity of British coin. Prof. Brande concluded by calling at- 

 tention to the manner in which the operations of the Mint ensured the quick 

 production of coin of unimpeachable weight and fineness ; how loss of inte- 

 rest on bullion was obviated ; a national panic prevented by the rapidity of a 

 coinage, which, though so quickly accomplished, will bear comparison, as to 

 execution, with that of any country in the world. 



PROFESSOR FARADAY ON THE LIQUEFACTION AND SOLIDIFICA- 

 TION OF GASEOUS BODIES. 



On Friday evening, Jan 31, Professor Faraday delivered a most interesting 

 lecture, at the Royal Institution, in Albemarle-street, on the liquefaction and 

 solidification of gaseous bodies. Before commencing his lecture he read an 

 extract from a letter written by Professor Liebig, of Giessen, shortly after his 

 visit to this country, in which the learned writer said, the thing which struck 

 him most in England was the persuasion that only those works that had a 

 practical tendency attracted attention and commanded respect, whilst those 

 which were purely scientific were almost unknown ; and yet the latter were 

 the true sources from which the others flowed. In Germany, added Liebig, 

 it was the contrary; but he did not say that that was better — in his opinion 

 the golden medium was the proper course. 



Mr. Faraday then proceeded v»ith his lecture. The condensation of gases 

 (said he) had been brought before the public some years ago. A gas was 

 one of those substances in an aerial form which remained permanent under 

 the ordinary circumstances of temperature and pressure, whilst vapour was 

 like gas, Init which under ordinary circumstances was condensable again into 

 liquid. It was at one time thought that all gases were perfectly elastic fluids, 

 but by his researches he had succeeded in turning into vapour the following 

 nine gases, namely,— chlorine— muriatic acid — sulphurous acid— sulphuretted 

 hydrogen — carbonic acid — euchlorine — nitrous oxide^ — cyanogen — and am- 

 monia. One of these, namely, carbonic acid, the late celebrated Thilorier, of 

 Paris, had, after many experiments, obtained in a solid state, and Bunsen had 

 subsequently obtained also cyanogen in a similar condition. But although 

 continued attempts have been made to solidify the other seven, and by im- 

 mersion in deep water a pressure of 200 atmospheres, i. e. of 3,0001b! to a 

 square inch, had been produced, still they had been unattended with success. 

 He would explain what be believed to be the reason of the failure. If he 



took a bottle half filled with ether (and this was Latour's experiment) and 

 applied to it heat, the ether would rise in vapour, and so would continue 

 until the vapour was much condensed. At last, the liquor below and the 

 vapour above would be of as nearly the same weight as possible, and the 

 least degree of additional heat would turn the liquor into vapour, or, if taken 

 away, convert the vapour into liquor. Observe what happened. At that 

 temperature of ether no pressure could bring the vapour into a liquid state ; 

 at a lower temperature it would. He believed, then, the reason why so many 

 had failed in liquefying and solidifying gases was, that although they 

 could procure the immense pressure mentioned, they could not obtain a 

 degree of temperature sufficiently low. He would explain in what manner 

 be had suceeetlcd. He had taken as his basis carb(}nlc acid gas in its sohd 

 state as produced by Thilorier. A quantity of carbonic acid, in partly a 

 liquid and partly a vapour state, being confined in a tube, the expansion of 

 the vapour forced the liquid through an orifice in the side into a cylindrical 

 brass box, and by the cold produced by the expansion of the gas, a part of 

 it was immediately converted into a solid substance like snow. Its tempera- 

 ture in that state was 70 degrees below of Fahrenheit ; but though he took 

 that iis his basis, it was not low enough for the purpose of bis experiments. 

 The temperature must, therefore, be further decreased. It had been demon- 

 strated by Thilorier, that if ether were applied to solid carbonic acid, the 

 temperature could be reduced to even 103 degrees below Fahrenheit; but a 

 lower degree was still required, and that was obtained by exhausting the 

 air. His object, then, was to combine this extreme degree of cold with great 

 pressure in his experiments on gases. The means by which he effected it be 

 thus described ; — -A quantity of gas in a glass vessel was forced by a con- 

 densing pump into a tube inserted in the receiver of an air pump ; that part 

 of the tube inserted in the receiver was made of common bottle glass (the 

 strongest kind for experiments, and capable of bearing an enormous pressure) 

 in the shape of a retort, and the bent or lower part of the tube lying im- 

 mersed in the cold bath (produced by solid carbonic acid combined with 

 ether, after the air had been exhausted), gas in a liquid, and by an increased 

 degree of pressure, in a solid state could be obtained. 



The learned professor illustrated the truth of the principle by producing 

 olefiant gas in a liquid state, and observed that he had succeeded in obtaining 

 in the same condition phosphuretted hydrogen, hydriodic acid, hydrobromic 

 acid, fluoboron and fluosilicon; and iu a solid form sidphurous acid, sul- 

 phuretted hydrogen, euchlorine, nitrous oxide, hydriodic acid, and hydro- 

 bromic acid. He had made carbonic acid the type of the others, but he 

 thought nitrous oxide would give a power of temperature as far below car- 

 bonic acid as that was below common ice. He saw no reason why the same 

 result might not be obtained from oxygen, hydrogen, and nitrogen ; and, in 

 fact, he had hoped that evening to have shown oxygen in a liquefied state, 

 but he had failed in his experiments, not because his principle was wrong, 

 but from the porous and hence imperfect nature of the vessels used. With 

 respect to hydrogen, he had had indications in the course of his experiments 

 that it would be found to be a metal of a most subtle nature. 



As this subject is one of considerable importance, we give the letter of 

 Professor Faraday to M. Dumas, describing the mode of performing the ex- 

 periments. 



" I sought in the first place to obtain a very low temperature, and employed 

 for this purpose Thilorier's bath of sohd carbonic acid and a;ther, placing it 

 however under the recipient of an air-pump. By maintaining a constant 

 vacuum, I lowered the temperature to such a degree, that the carbonic acid 

 of the bath was not more volatile than water at the temperature of 86", for 

 the barometer of the air-pump stood at 28-2 inches, the external barometer 

 being at 29-4. 



This arrangement made, I joined together, by means of corks and stop- 

 cocks, some small glass and copper tubes, so that with the aid of two pumps 

 I was able to subject various gases to a pressure of 40 atmospheres, and at 

 the same time to submit them to the intense cold obtained under the air- 

 pump, and to examine the resulting efteets. As I expected, the cold pro- 

 duced several results which pressure alone would never have done, and prin- 

 cipally in the solidification of bodies ordinarily gaseous. The following is a 

 sketch of the various results : — 



Olefiant gas was condensed to a beautiful colourless transparent liquid, 

 but it did not solidify; it dissolves the resinous, bituminous and oily bodies. 



Pure hydriodic acid may be obtained either in the solid or liquid state. 

 Solid hydriodic acid is very clear, colourless and transparent ; generally 

 several fissures traverse the mass ; it greatly resembles ice. 



Hydrobromic acid may also be obtained either as a limpid and coloiurles* 

 liquid, or as a clear transparent solid. 



Both these acids require a very careful distillation in closed vessels and 

 under great pressure, to be obtained pure and colourless. 



Fhwsilicic acid was condensed to the liquid state, but it is repuisite to 

 operate at the lowest temperature. It is extremely liquid and mobile, like 

 hot a;ther ; it then produces a pressure of about atmospheres, and gives 

 no sign of solidification. It is transparent and colourless. 



Fluoboric acid and phosphureited hydroyen presented some results of con- 

 densation. 



Hydrochloric acid liquefies readily at less than 1 atmosphere of pressure, 

 but it does not solidify. 



Sulji/inrrms acid freezes immediately, as was to be expected. 



Sulphuretted Itydrogen becomes solid, and then forms a white, transparcnl, 

 crystalline mass, bearing greater resemblance to solid nitrate of ammonia or 

 to camphor, than to ice, 



