It* 



OASES, LIQUEFACTION OF. 



OASOMETHI 



116 



When the current hM been continued for a sufficient length 

 of time it i* interrupted, and the tube U rapidly sealed up hermetically, 

 by the application of a mouth-blowpipe flame to the narrowest 

 portion*, a a. 



Cvllrrtion of gam by fK*plaeeme*t of motor. This is by far the most 

 common method in UM, although without great care and the employ- 

 ment of recently boiled water it U impossible to preserve the gas free 

 from admixture with air, because all gases being more or lew soluble 

 in water, a transference of the gai into the air, and met vend, is con- 

 stantly taking place through the confining liquid. The most simple 

 mode of collecting gases by this process consist* in filling a glass jar, 

 such as that shown injiy. 1, with water, inverting it on the shelf of a 

 pneumatic trough, and then bringing the extremity of the gas delivery 

 tube beneath the mouth of the jar ; the gas then bubbles through the 

 water, ascends into the upper part of the jar, and displaces the water 

 with which the latter was previously tilled. 



Larger quantities of gases arc collected in gatliuldert, or gammrteri, 

 by this method. /'/;/. 4 represents the gasholder most generally em- 



: .. i. 



ployed for experimental purpose). It con- 

 sists of a cylindrical copper vessel, closed at 

 top and bottom, and at about U inches above 

 it a second shorter cylinder, open at top, is 

 fixed upon suitable supports. The two cylin- 

 ders are connected by means of two tubes, 

 m, n, furnished with stopcocks; m passes 

 nearly to the bottom of the lower cylinder, 

 whilst n terminates under its cover. At / 

 there U also a stopcock and short tube, and 

 at i there is a larger orifice which can be 

 securely closed by means of a screw-plug. 



To use this gasholder, the plug i must be 

 screwed into its place, all the stopcocks 

 opened, and water poured into the upper 

 cylinder. The water will descend through 

 the tube m, and expel the air from the lower 

 cylinder through the stopcocks, n, / ; when 

 water issues from the latter, the lower cylin- 

 der is filled :m,, and / must now be closed, 

 and the screw-plug, t, being removed, the 

 apparatus is ready for the collection of gas. The tube conveying the 

 latter must be inserted into i ; the bubbles will now ascend to the 

 upper part of the cylinder, displacing a corresponding volume of 

 water, which will flow out of i. The quantity of gas collected is 

 conveniently seen by means of the glass gauge-tube, </. When the 

 necessary amount of gas has thus been received in the holder, the 

 delivery tube U removed from i, and the screw-plug replaced. The 

 gas may at any time be expelled from this holder 1'or experimental 

 purposes, either through the tube n into jars filled with water and 

 inverted over its orifice, or through i in a continuous stream, which is 

 often desirable. The expulsion of the gas through either of these 

 orifices is effected by opening the stopcock, m, and keeping the upper 

 cylinder supplied with water. It is scarcely necessary to remark that 

 such gases only as are sparingly soluble in water con be collected by 

 this process. 



riion of gate* by displacement of m-n(ify. This is by far the 

 best process for the collection of gases in a state of perfect purity, 

 although it is less frequently employed than the other two processes, 

 owing to the difficulty of manipulating with a heavy fluid like mercury. 

 The process exactly resembles in principle the collection by displace- 

 ment of water, but owing to the high specific gravity of mercury, 

 vessels of small size only can be used ; hence glass tubes of a diameter 

 varying from half an inch to 14 inch are generally employed. Care 

 must be taken not to allow the gas-delivery tube to dip too deep into 

 the metal, otherwise the great pressure upon the gas-generating appa- 

 ratus may endanger the tightness of the joints. This method may be 

 applied to all gases except i-ld.irine and hydrofluoric acid. 



In addition to these methods of collection, many gaaes may be con- 

 veniently stored up in caoutchouc or mackintosh bags, when purity is 

 not of importance ; but they should not be retained in such bags more 

 than 48 hours, otherwise they become mixed with considerable quanti- 

 ties of air. Care should be taken not to collect coal-gas in caoutchouc, 

 ta the latter becomes softened and partially dissolved. 



OASES, LIQUEFACTION OF. We are indebted chiefly to Pro- 

 fessor Faraday for our knowledge of liquified and solidified gases. 

 The method which he employed consisted in combining the condensing 

 power of mechanical compression with that of very considerable de 

 pression of temperature. The first object was attained by the succes 

 sivc action of two air-pumps ; the first having a piston of one inch in 

 diameter, by which the gas to be condensed .was forced into the 

 cylinder of the wound pump, the diameter- of whose piston was only 

 half an inch. The tubes into which the air, thus further condensed, 

 was made to pass, were of green bottle-glass, from one-sixth to one 

 quarter of an inch in external diameter, and had a curvature at one 

 portion of their length adapted to immersion in a cooling mixture 

 they were provided with suitable stopcocks, screws, connecting pieces, 

 and terminal caps, sufficiently air-tight to sustain a pressure of fifty 

 atmosphere*. Cold was applied to the curved portions of the tube by 

 their immersion in a bath of Thilorier'a mixture of solid carbonic acid 



and ether. The degree of cold thus produced, when the mixture w* 

 surrounded by the air, was 106* Fair., by an alcohol thermometer. 

 Hut on placing the mixture under an air-pump, and removing the 

 atmospheric pressure, leaving only that of the vapour of carbonic acid, 

 which amounted only to one twenty-fourth of the former (that is, to 

 .he pressure of a column of 1'2 inch of mercury), the thermometer 

 ndioated 166 below zero. In this state the ether was very fluid, and 

 JIB bath could be kept in good order for a quarter of an hour at a 

 time. Mr. Faraday found that there were many Jism which, on being 

 subjected to cold of this extreme intensity, condensed into 1. 

 even without a greater condensation than that arising from the 

 ordinary atmospheric pressure, and they could then be preserved, 

 sealed up in glass tubes in this liquid state. Such was the case with 

 chlorine, cyanogen, ammonia, sulphuretted hydrogen', arseniuretted 

 lydrogen, hydriodic acid, hydrobromic acid, carbonic acid, and 

 euchlorine. With respect to some other gases, such as nitric oxide, 

 duoride of silicon, and olefiant gas, it was difficult to retain them for 

 any length of tune in the tubes, in consequence of the chemical action 

 they exerted on the cements used in the joinings of ca], and other 

 parts of the apparatus. Hydriodic and hydrobromic acids could be 

 obtained either in a solid or liquid state. Hydrochloric acid gas did 

 not freeze at the lowest temperature to which it could be subjected. 

 Sulphurous acid froze into transparent and colourless crystals, of 

 greater specific gravity than the liquid out of which they were formed. 

 Sulphuretted hydrogen solidified in masses of confused crystals of a 

 white colour, at a temperature 122 Kalir. Kuchlorine was easily con- 

 verted from the gaseous state into a solid crystalline body, which by a 

 slight increase of temperature melted into an orange red fluid. Nitrous 

 oxide was obtained solid at the temperature of the carbonic acid l.uth 

 in nt'-un, and then appeared as a beautifully clear and colourless 

 crystalline body. Mr. Faraday conceives that in this state it might, 

 in certain cases, be substituted with advantage for carbonic acid in 

 frigorifie processes, for arriving at degrees of cold far below those 

 hitherto attained by the employment of the latter substance. Ammonia 

 was obtained in the state of solid white crystals, and retained this 

 form at a temperature of 103". The following liquids could not 

 be made to freeze at 166 : chlorine, ether, alcohol, bisulphide of 

 carbon, caoutchoucin, camphor, and rectified oil of turpentine. 



The following table, chiefly from Miller's ' Elements of Chemistry,' 

 shows the points of liquefaction and solidification of various gases : 



Hydrogen, nitrogen, carbonio oxide, and nitric oxide, have been sub- 

 mitted to pressures of upwards of 800 atmospheres without exhibiting 

 signs of liquefaction. 



QA8HOLDBB or GASOMETER [OAS, MAHCFACTURK OP.] 



i. \snMKTr.U. [UASES, COLLECTION OK.] 



GASOMETR1C AN A I . V s i S. <ia analyst*. Jiiidinmttriral analytit. 

 ir,i. This branch "t chemical 'analysis originated in 'the 

 attempts of Fontana, Landriani, Schecle, 1'riestley, Oay Lussac, and 

 others, to determine the volume of oxygen in samples of atmospheric 

 air taken from various localities. The imperfect methods then used 

 led these observers to believe that there was considerable dillcrence in 

 the per-centage of oxygen contained in the air resting over different 

 portions of the earth's surface, and it was imagined that these dill'er- 

 ences were closely connected with the unhealthiness or salubrity of 

 various places. Hence the name eiutiomcter (from 6Jioj and /itrptir, 

 measurer of the goodness of air) was given to the instrument used for 

 these determinations. 



The principle upon which the use of the eudiometer was made to 



depend, so far as atmospheric air and oxygen gas .-.- I, wax 



that of exposing them to the action of some M .<|I.T solid, 



fluid, or gaseous, which, on account of its affinity for oxygen, com- 



j bined with the hitter, leaving the gases with which it was mixed 



The eudiometer invented by Dr. Priestley arose from, and was con- 

 nected with, his great discovery of oxygen gas and the fact which lie 



