1820.] Specific Gravity of Gases. 255 



to the thin film of air which adheres with obstinacy to the inside 

 of the glass. Indeed unless the mercury were previously boiled 

 in the jars, I question whether it would be possible to procure 

 the cyanogen purer than we got it. Gay-Lussac's result is 

 within less than TruVo-tl^ P^^"^ of the truth. His error is in excess, 

 mine in deficiency. If we were to take the mean of the two, 

 we should get 1-805175 for the specific gravity of cyanogen — a 

 number which does not differ much more than vijVoth part from 

 the truth. I consider this to be as near an approximation to 

 absolute precision as we can well attain in such experiments. 



Cyanogen is a ternary compound consisting of two atoms of 

 carbon and one atom of azote; so that the weight of an integrant 

 particle of it is 3-25 ; for 



2 atoms carbon = 1*50 



1 atom azote = 1"75 



= an atom of cyanogen. 



If we make the specific gravity of oxygen gas unity, then the 

 specific gravity of cyanogen will be reduced to 1-625. Now 

 1-625 X 2 = 3-25; so that the weight of an atom of cyanoo-en 

 is precisely double its specific gravity. In this respect it agrees 

 with the greater number of the gases mentioned in the preceding 

 part of this essay. 



The gaseous constituents in cyanogen are reduced to one- 

 third of their original volume. This proves the strong affinity 

 which exists between them, and the intimacy of the combination 

 which they form. 



6. Chlorocarboiiic Acid. — This gas was discovered by Dr. 

 John Davy. It may be formed by mixing together equal 

 volumes of carbonic oxide and chlorine gas, and exposing the 

 mixture to the direct rays of the sun inclosed in a glass jar. 

 The colour disappears, and the bulk of the mixture is reduced 

 to one half. This was the process employed to form it in my 

 laboratory. In consequence of the difficulty attending the pro- 

 cess, we were satisfied with a single trial, which gave us the 

 specific gravity of this gas 3-4604. 



I am not aware of any previous attempt to determine the spe- 

 cific gravity of this gas experimentally ; but it is obvious that its 

 true specific gravity is just equal to the specific gravity of 

 chlorine gas + the specific gravity of carbonic oxide gas. 



Sp. gr. of chlorine gas = 2*5 



carbonic oxide gas .... = 0-9722 



3-4722 

 = specific gravity of chlorocarbonic acid. 



Our determination is about j^th part less than the truth, and 



