1825.] Di\ Thomson's Answer to Mr, Itcuni/, 357 



cium. To prevent this, that tube was made to pass through 

 a perforated cork fixed in the beak of a tubulated retort containing- 

 some sulphuric acid, while a sewing thread doubled was inserted 

 between the tubulure and the glass stopper to ajljow the hydrogea 

 gas to escape as it was evolved. <^^ ri§P3v 



The third tube containing chloride of^dalciu'm, which was 

 furthest from the flask, had undergone no alteration whatever in 

 weight. I concluded from this that three feet one inch of tube 

 filled with chloride of calcium was sufficient to render the 

 hydrogen gas as dry as it could be made by this method. In 

 consequence of this in a subsequent experiment, I omitted the 

 third tube altogether. ^n-^itiw u^ i oimtnsrngr^ fojue 



The increase of weigliti$fi<lf^ s«con?d[t(iT3e^^ .'. . . 0*1 gr. 



; / ni Q'wisiw first tube 0*84 



i oj DionnodiitnnLf dBd'NSiUOR by >;-.| |k ii — 



Mioo ym wmb oi bne .8tn6rane3^fet%lfe*Wii '4c»^y 0*94 



oi .e' - ;w 1 .rijn-^ b''« 



bnoii; The loss of flask wa^j^^j^f ^.j, .^. •: 4*8 grams. 

 ; p.udi bnfi^ain of tubes ,^,.3^ •3fk.-f^iy(T^^*ix>PM'K^ ■. 



' ^^^^^^ %eight of hydrog^ g^g^';. . ??.^W^;^ ' , 



'^l^ov^ 130*21 : 100 :: 3-86 : 2*964 =2^ iveight ;of gas evblved 

 during the solution of 100 grains of zinc; and 130*21 : 100 :: 

 0*94 : 0*7219 = moisture deposited in the tube during the 

 solution of 100 grains of zinc in dilute sulphuric acid. The 

 volume of this gas being 138'7o51 cubic inches, it is easy to see 

 that when the barometer stands at 30 inches, and the thermo- 

 meter at 60°, the weight of 100 cubic inches of hydrogen gas is 

 2*136 grains. 



According to this determination the specific gravity of oxygen 

 gas is to that of hydrogen gas as 16 to l-'OO??. This deviates 

 _.^th part frOm the ratio 1 to 16 ; and this ratio will be exact, if 

 it be admitted that an error amounting to 0-02 grain was con- 

 mitted in the weighing.* 



If we calculate the weight of vapour which the hydrogen gas 

 ought to have carried off from the dilute acid, we shall find it to 

 amount to 0*313128 grain; but the moisture imbibed by the 

 chloride of calcium amounted to 0*94 grain, or three times the 

 calculated quantity. We must, therefore, either admit that our 

 notions respecting vapour are still imperfect ; or that the hydro- 



* It is reasonable to expect that the specific gravity of hydrogen gas as determined 

 ejipferimentally will be a little higher than the theoretical weight, because it is'almost 

 impossible to prepare it absolutely pure, and every impurity must necessarily increase 

 its weight. The zinc which I employed, though it had been distilled in an earthenware, 

 retort, was by no riieans absolutely pure; for I could still detect in it minute quantities 

 of foreign matter. Now it is surely not at all unlikely that so great a Tolume of hydro- 

 gen as 187 cubic inches might contain 0-02 grain of foreign matter. This is all the 

 impurity which it is requisite to admit on the supposition tibiat no error whatever wa^ 

 committed in the weighing, - * 



