WATER TYPE. 9 



weight of two litres of hydrochloric acid gas, for instance, proving 

 to be identical with the weight of one litre of chlorine, plus that 

 of one litre of hydrogen, it is evident that mixed hydrogen and 

 chlorine on becoming combined hydrogen and chlorine occupy 

 precisely the same bulk before and after combination. 



(8.) Turning our attention next to the combination of hy- 

 drogen with oxygen, we find that when oxygen and hydrogen 

 gases unite with one another to form water, it is always in the 

 proportion of one volume of oxygen to two volumes of hydrogen ; 

 and, conversely, when we decompose water electrolytically into 

 its constituent gases, we find that for every single volume of 

 oxygen liberated at the one pole, we have two volumes of hy- 

 drogen liberated at the other. Experiment has proved over and 

 over again that just as chlorine and hydrogen will unite with 

 one another only in the proportion of volume to volume, oxygen 

 and hydrogen will unite with one another only in the proportion 

 of one volume of the former to two volumes of the latter gas. 

 But oxygen is found to be exactly 16 times heavier than hy- 

 drogen ; or, taking the specific gravity of hydrogen as unity, the 

 specific gravity of oxygen will be 1 6 ; or, calling the weight of a 

 litre of hydrogen I crith, the weight of a litre of oxygen will be 

 1 6 criths. Hence, in water we have two volumes of hydrogen 

 united with one volume of oxygen, or 2 parts by weight of 

 hydrogen united with 16 parts by weight of oxygen, thus: 



Water 



When, however, two volumes of hydrogen unite with one 

 volume of oxygen, they do not form three volumes, but only 

 two volumes of gaseous water or steam. That is to say, the 

 three volumes of mixed hydrogen and oxygen form only two 

 volumes of combined hydrogen and oxygen. This condensation 

 is capable of being shown by direct experiment, but really we 

 do not require any such experiment, since the result may be 

 demonstrated with equal certainty by observing the specific 

 gravity of steam. We find, for instance, that the weight of two 



