CORRECTIONS FOR MOISTURE IN GAS. 51 



inches, which, corrected to the temperature of 60, becomes 2 - 942 cubic inches. 

 The whole volume corrected to mean temperature and pressure will be found 

 to equal 219'929 cubic inches, from which if the 2'942 cubic inches of aqueous 

 vapour be subtracted, there will remain 216'987 cubic inches as the volume of 

 dry gas at mean temperature and pressure ; 2,940 cubic inches of aqueous 

 vapour weigh '5675 grains, for 2'942 X 0'1929 = 0'5675; this subtracted 

 from 101 '69, the whole weight, leaves 101 '122 5 grains, which is the weight of 

 the 216'987 cubic inches of dry gas; and by the simple rule of proportion, 

 therefore, it will be found that 100 cubic inches of such gas, when dried, and 

 at a mean temperature and pressure, will weigh 46'603 grains. 



Some experimenters prefer drying the gas before it is weighed, and thus in 

 fact weigh a known volume, not of a mixture, but of a pure gas. Now gases 

 are dried in various ways ; one method is to pass them through a glass tube, 

 containing substances having a powerful attraction for water : it is a simple 

 and a useful process, and therefore proper to be described here, though not 

 conveniently applicable to the mode of weighing a gas as above directed, be- 

 cause of the greater difficulty of measuring the quantity of gas which enters. 

 The tube may be about half an inch in diameter, and two feet long, and should 

 have a piece of wire pressed into a loose ball thrust into one end of it, to pre- 

 vent fragments falling through. Chloride of lime should be heated and fused 

 in an earthenware crucible a temperature below that of visible redness being 

 quite sufficient for the purpose then poured upon a clean metallic or stone 

 surface, and, as soon as it has solidified, broken up and put into stopped 

 bottles. This chloride, being divided into a mixture of large and small frag- 

 ments, is to be introduced rapidly into the tube, until the latter is nearly full ; 

 the apparatus is then ready for use. The tube may be connected with the jar- 

 gasometer, or other vessel containing or evolving the gas, by caoutchouc con- 

 nectors, or in any other convenient way ; and so much gas should be passed 

 through it, as effectually to expel all the common air before the globe or vessel 

 to be filled with the dry gas be attached. That being done, the gas should 

 be allowed to pass slowly, 100 cubic inches having about ten minutes al- 

 lowed for their passage through such a tube as that described ; though if the 

 period be lengthened, no injury is occasioned. If the tube be shorter, or of 

 smaller diameter, more time should be proportionably allowed. Dr. Thomson 

 has published a very useful method of weighing gases in the Annals of Phi- 

 losophy, vol. xv. p. 352. 



H2 



