1820.] Specific Gravity of Gases. 175 



Biot and Arago. 0'59669 



Davy 0-590164 



Of all these experiments that of Davy, which is the latest, 

 approaches most nearly to the theoretical specific gravity. The 

 deviation indeed does not amount to so much as -rwoth part. 

 This beino- greatly within the limits of unavoidable error in such 

 experiments, it seemed hardly necessary to repeat the trials, as 

 there was no probability of coming nearer the truth. However, 

 three experiments upon the specific gravity of this gas vi'ere made 

 in my laboratory with every attention to accuracy naturally sug- 

 gested by the gas under examination. The results were as 

 follows : 



By first trial 0-5933 



By second trial 0-5930 



By third trial 0-5930 



The mean of these three trials gives 0-5931 as the specific 

 gravity of ammoniacal gas. This exceeds the truth by about 

 ^r-gio-th part— a fraction greatly within the limits of unavoidable 

 eiTor from the experiment. As this result is upon one side of the 

 theoretical number, while Sir H. Davy's is on the other, they 

 serve mutually to confirm the accuracy of the theoretical result, 

 and to confirm the notion of the constitution of ammoniacal gas 

 derived from the general law discovered by Gay-Lussac. Were 

 we to. take the mean of the specific gravities obtained by Sir H. 

 Davy and myself, we should obtain for the specific gravity of 

 ammoniacal gas 0-590237, a number which does not differ so 

 much as -^^Jj-jj-j^th part from the one derived from theory. This 

 is an approxunation near enough, I conceive, to satisfy the most 

 scrupulous mind. No person who has paid the requisite atten- 

 tion to the facts can entertain the least doubt that annnoniacal 

 gas is a compound of one volume of azotic gas and three volumes 

 of hydrogen gas condensed into two volumes, and that its true 

 specific gravity is 0-59027. 



4. Muriatic" acid gas is known to be a compound of one 

 volume of chlorine and one volume of hydrogen gas united with- 

 out any alteration of volume. Hence its specific gravity must 

 be the mean of the specific gravities of chlorine gas and hydro- 

 gen gas. 



Specific gravity of chlorine gas 2-5000 



hydrogen gas .... 0-0694 



2)2-5694 



1-2847 



Its specific gravity, therefore, must be 1-2847. It was deter- 

 mined both by Sir H. Davy and Gay-Lussac, and found by both 

 of these chemists to be 1-278. This differs from the theoretical 



