The Chemical Relations of Water 



301 



are injurious when breathed, may not escape into the 

 air. When the above experi- 

 ment is performed under these 

 new conditions the contraction 

 in volume which occurs after 

 the explosion is found to equal 

 the volume of the oxygen in- 

 troduced, a further contraction 

 of twice this amount being 

 effected by allowing the ap- 

 paratus to cool. From these 

 observations it would appear 

 that the volume of steam 

 formed by the combination of 

 two volumes of hydrogen with 

 one of oxygen itself occupies 

 a volume equal to that of the 

 hydrogen. 



206. A great many ex- 

 periments have been performed 

 with the object of finding the 



Fig. 101. 



composition of many other bodies besides water, both 

 by volume and by weight, and one general result of 

 these may be summed up as follows : 



In every chemical compound the ratios between 

 the weights of the elements contained in the compound 

 are constant. 



This statement is known as the " Law of Constant 

 Composition " and is entirely the outcome of experi- 

 mental work. No theory of the constitution of matter 

 is involved in any way in the evidence for the validity 

 of the law. 



As examples of what is implied by this law we will 



