176 !)/•• Thomson on the [Sept 



result about -5-^ o^th part, and leads to the suspicion that the gas 

 which they experimented upon was not pure, but in reality a 

 mixture of about 98 volumes of muriatic acid and two volumes 

 of common air ; at least such a mixture would have the specific 

 gravity indicated by them. 



Three trials were made in my laboratory with muriatic acid 

 gas prepared with every attention to ensure its purity. The 

 results were as follows : 



By first trial 1-2843 



By second trial 1-2844 



By third trial 1-2844 



The mean of these gives 1-284366 for the specific gravity of 

 muriatic acid gas. This number differs from the theoretical 

 number by httle more than-j-jJjj^^th part. This number being far 

 within the limits of unavoidable error, we are warranted to con- 

 clude without any hesitation that muriatic acid is a compound 

 of equal volumes of chlorine and hydrogen gases united without 

 any change in their volume, and that its specific gravity is 

 1-2847. 



This paper has already extended to such a length that it will be 

 proper to reserve the statement of the remaining gases whose 

 specific gravities have been ascertained in my laboratory, amount- 

 ing in number to 12, to another opportunity. I shall conclude 

 the present paper with exhibiting a table of the true specific 

 gravities of the nine gases which have come under our review, 

 together with the experimental results which have been obtained, 

 and the difference between the true numbers and the experi- 

 mental ones. 



Gases. 



Oxygen 



Azotic 



Hydrogen 



Chlorine 



Protoxide of azote. . . , 

 Deutoxide of azote. . . 

 Protoxide of chlorine. 



Ammoniacal 



Muriatic acid 



True specific 

 gravities. 



1-11110 

 0-97220 

 0-06940 

 2-50000 

 1-52770 

 1-04160 

 2-44440 

 0-59027 

 1-28470 



Specific grav. ob- 

 tained by exper, 



1-1117 



0-9728 



0-0694 



2-5000 



1-5269 



104096 



2-4015 



0-590237 



1-284366 



Difference. 



1 J o 





 



i 



1 



10 



I I 



In order to draw the particular attention of chemists to this 

 subject, I need only mention that in the present state of the 

 science it is of the very first importance. It is only by means of 

 it that we can arrive at precise numbers for the atomic weights 

 of bodies, and thus form an accurate basis upon which a true 

 science can be reared. The methods followed by Dr. Wollaston, 



