ANALYSIS OF COMPLEX MATTER 141 



hydrogen coming in contact with it. The tube D is also 

 weighed, with the same precaution as before, and the increase 

 of mass is due to the water which has been formed by the 

 union of the oxygen and hydrogen. The relative quantity of 

 hydrogen, entering into the composition of water, is indirectly 

 denoted by the difference between the quantity of water 

 formed and the quantity of oxygen yielded up by the copper 

 oxide. 



In this experiment we assume that the hydrogen is pure 

 that the matter taken away from the copper oxide is oxygen ; 

 and that this oxygen is afterwards retained wholly in the tube 

 D in combination with hydrogen. 



93. Different Relative Quantities of the same kinds of 

 Matter may combine Chemically. In describing the law of 

 definite proportions, it is important to state that the same 

 relative quantities of constituents are only to be found in the 

 same compound, since different compounds may be formed 

 of precisely the same kinds of matter. It remains to be 

 shown under what circumstances the same kinds of matter 

 may combine chemically, and produce compounds differing in 

 properties. We may take, as an example, two compounds of 

 lead and oxygen, lead monoxide and lead dioxide. 



In precisely the same manner as copper oxide was analysed, 

 by raising its temperature in the presence of hydrogen, lead 

 monoxide and lead dioxide may now be analysed, and the 

 relative quantities of their constituents found. We observe 

 that, in the lead dioxide, there is double the relative quantity 

 of oxygen that there is in the lead monoxide. In all other 

 examples that are examined, it will be found that the relative 

 quantities of the constituents in one compound are related in 

 a simple manner to the relative quantities of the same consti- 

 tuents when they happen to form another distinct compound. 



These two compounds are considered as different kinds of 

 matter for the following reasons : they differ in appear- 

 ance (one is yellow, the other dark brown) ; their densities 

 are unlike ; their behaviour when placed in contact with 

 other bodies is not the same (their chemical behaviour differs). 



The most striking examples that can be given of this law 



