128 Revieio of Dr. Thomson 



blunders. His own result, in reality, gives 2.002 grains for the 

 weight of 100 cubic inches of dry hydrogen (bar. 30, therm. 60°), 

 whence the following proportion : — 2.002 : 33.915 : 1 : 16.9, a 

 number which, if true, would utterly subvert Dr. Prout's theory. 



But it is time to return to his estimate of the specific gravity of 

 vapour at 49° bar. 30.1. He states it, most erroneously, at 

 0.00533. Let us take (as he does) Mr. Dalton's number, 0.363, 

 for the elastic force of aqueous vapour at 49° Fahr. Now, the 

 true specific gravity of such vapour, according to the principles 



so clearly established above, is 0.0075625 s= — - ' air 



30 



at 49° = 1.000000. But in reference to air at 60° = 1, the num- 

 ber becomes 0.00773 ; for the density of air at 49° is to that at 

 60° as 508 : 497 ; whence we have this proportion : 

 497 : 508 :: 0. 0075625 : 0.00773. 

 Hence the weight of moisture in his 136. 8S cubic inches (or 3 

 grains) of hydrogen gas is 0.00773 X 136.8S x 0.305 gr. = 0.3227. 

 But the muriate of lime intercepted (he says) 0.163 gr. ; therefore 

 0.3227 — 0.163 — 0.1597 of a grain must have remained in the 

 hydrogen, assuming his experiment to have been accurately made. 

 Thus we see that about one-half of the moisture escaped the ac- 

 tion of the calcareous muriate, so that its presence merely com- 

 plicated the result. Deducting from 3 grains, which is the whole 

 weight of humid hydrogen disengaged from the flask, the 0.3227 

 of a grain of aqueous vapour, we have a remainder of 2.6773 

 grains, for the weight of dry hydrogen, whose bulk, he says, 

 would have been at 60° Fahr., 138.7551 cubic inches. Hence 



2 6773 



~r-^ = 1.9295. This, therefore, is the weight of 100 cubic 



1.387551 



inches of dry hydrogen, by Dr. Thomson's experiments at 30 

 bar, and 60° therm. And J. 9295 : 33.915 :: 1 : 17.57. " This 

 approaches (not) so nearly the ratio of 1 : 16, as to leave no 

 doubt that the specific gravity of oxygen gas is exactly 16 times 

 greater than that of hydrogen gas." Consequently, the specific 



gravity of hydrogen gas is— = 0.0632 ; a very different re- 



17.57 



suit indeed " from the specific gravity already deduced by Dr. 

 Prout (0.0694), and which I obtained experimentally, as may be 

 seen in my paper on the specific gravity of gases*." 



Of the result to which he here refers, and which is given in the 

 16th volume of his Annals, p. 168, it is sufficient to say, that he 

 found the specific gravity of moist hydrogen, compared to that of 

 moist air, to be by experiment as 0.0694 to 1.000 1, though Dr. 



* Thomson? s Attempt, i. 71. 



t The Doctor's estimate of the equation for vapour being- about j^j of the 

 real quantity, he accommodated his experiment to this fallacious judgment ! 



