8 ANIMAL CHEMISTRY LECTURE I. 



the tube is now manifested to you by its complete solution in the 

 water, and by its action upon colouring matter. But, if instead 

 of allowing the two gases to act upon one another slowly in 

 diffused daylight, we expose them to direct sunlight, or if we 

 bring them into contact with flame, their combination then takes 

 place, as you see, instantaneously and with explosion. Now, it 

 has been shown over and over again, that when chlorine and hy- 

 drogen gases unite with one another to form hydrochloric acid, it 

 is always in the ratio of equal volumes. If we take one volume 

 of hydrogen and one volume and a quarter of chlorine, the one 

 volume of hydrogen unites with one volume of chlorine, and leaves 

 the extra quarter volume of chlorine unacted upon. In the same 

 way, if we mix together one volume of chlorine and one volume 

 and a quarter of hydrogen, the one volume of chlorine unites 

 with exactly one volume of hydrogen to form hydrochloric acid, 

 leaving the extra quarter volume of hydrogen unacted upon. Try 

 the experiment how we please, we come to the same conclusion, 

 that chlorine and hydrogen gases will unite only in the proportion 

 of volume to volume. But chlorine is exactly 35-5 times heavier 

 than hydrogen ; or, taking the specific gravity of hydrogen as 

 unity, the specific gravity of chlorine will be 35*5 ; or, if we call 

 the weight of a litre of hydrogen i crith, the weight of a litre of 

 chlorine will be 35*5 criths. Accordingly, in hydrochloric acid 

 gas we have one volume of hydrogen united with one volume of 

 chlorine, or I part by weight of hydrogen united with 35-5 parts 

 by weight of chlorine, thus : 



Hydrochloric acid 



Moreover, when hydrogen and chlorine gases unite with one 

 another to form hydrochloric acid gas, they undergo no alteration 

 whatever in bulk. If we take, for instance, a litre of hydrogen 

 and a litre of chlorine, we obtain exactly two litres of hydrochloric 

 acid. This persistence in bulk is capable of being shown by 

 direct experiment, but may be inferred with equal certainty by 

 merely taking the specific gravity of hydrochloric acid gas. The 



