{356 . Dr. Thomson's Answer to Mr, Rainy, [Nov. 



If we take 0'048 from 3, the remainder 2-952 will be the 

 weight of 138*7551 cubic inches of hydrogen gas. 



138-7551 : 100 :: 2-0'51 : 2-1274 « weight of 100 cubic 

 inches of hydrogen gas ; and admitting tiiat lUO cubic inches of 

 oxygen gas weigh 33*915 grains, the specific gravity of oxygen 

 gas is to that of hydrogen ga.s as 16 to. I'003(i. This deviates 

 less than -j-i-jjth from the ratio of 1 to 16. 



But a careful examination of my former experiments, which I 

 was induced to make by the perusal of Mr. Rainy's paper, led 

 me to entertain some doubts about the accuracy of this mode of 

 proceeding. Of ten experiments which I formerly made, nine 

 gave a greater augmentation of weight in the chloride of calcium 

 than the weight of all the vapour that could liave been contained 

 in the hydrogen gas at the temperature in which the experiments 

 were made. Now it appeared somewhat unreasonable to lay 

 aside nine-tenths of all the experiraents, and to draw my conclu- 

 sions from the odd tenth. J was desirous, therefore, to try 

 whether by increasing the length of tube filled with chloride of 

 calcium, 1 could not render the gas perfectly dry, and thus get 

 rid of the necessity of introducing the specific gravity of vapour 

 into the calculation. 



The experiments which I am going to give an account of were 

 four in number. They were made when the thermometer stood 

 at 60°, and the barometer at very nearly 30 inches, so that no 

 correction whatever was required for pressure or temperature. I 

 tilled three glass tubes with chloride of calcium, the two extre- 

 mities of each of which were stuffed in the usual manner with 

 amianthus. These tubes were united by slips of caoutchouc, 

 which were cemented into tubes by means of a solution of caout- 

 chouc in naphtha. The length of these tubes was as follows : 



' First tube 15 inches. 



Second tube 22 



Third tube 27 



Total length 64 



The zinc dissolved was 130*21 grains. 



Weight of flask with dilute acid . . 2780*7 grains 



' Weight of first tube 815*95 



Weight of second tube 1033*05 



Weight of third tube 1051*79 



The experiments were conducted precisely in the way already 

 ^^ tjg^^rib^d^ aud exactly the same precautions were. employed in 

 eaiiWi^i^Wng the t^bes: •♦md fl^sk. The ;>veMh.er b^^pp^ be 



-wiriirly^ 1 was afraid that some moisture might have insinuated 

 '''^i^iflhto the open end of the tube containing chloride of cal- 



ww i'i\'^ir,i\ff T(..i-. . "T f ^ ■ ■ i '^ .•■'.- 7;'::, 



gniiigbw 3ilJ ox bf^i'm 



