40 On the Dalton'mn Theory of [Jcly, 



doubts about its accuracy. It will be better to leave the investi- 

 gation of the subject till we come to examine the composition 

 of the different salts, in all of which the two constituents con- 

 tain oxygen. If it hold it will indicate a certain regularity in 

 the relative weights of the atoms of bodies which I have not yet 

 observed. 



(i. Water is capable of combining both with acids and bases. 

 When it unites with an acid it acts the part of a base, and con- 

 tains the same quantity of oxygen that the base would contain. 

 Therefore the least quantity of water that can combine with 

 sulphuric acid must contain 20 parts of oxygen. Hence the 

 strongest possible sulphuric acid is a compound of 



Acid 17±. 



Water 224 



100 



When the water combines with a base, it acts the part of an 

 acid, and combines in the same proportion. Hence such com- 

 pounds are called hydrates. This canon has also been laid down 

 by Berzelius. 1 must confess that I have not hitherto met with 

 sufficient evidence of its accuracy to induce me to put much 

 confidence in it ; but we shall be able to judge better when we 

 come to examine the constitution of the hydrates, than we can 

 at present. 



7- In combinations composed of more than two bodies con- 

 taining oxygen, the oxygen of that constituent which contains 

 the least of it is a common divisor of all the portions of oxygen 

 found in the other bodies. This law, likewise laid down by 

 Berzelius, evidently depends upon the kind of combination 

 which these bases make with oxyffen. If they are each combi- 

 nations of one atom of base with one atom of oxygen, the 

 quantity of oxvgen present in all will be the same. If one is a 

 protoxide, and another a deutoxide, then the one will contain 

 double the quantity of oxvgen in the other. And since oxygen 

 always unites by atoms, it is obvious that all the quantities of 

 oxygen will be divisible by one atom of oxygen. Hence the 

 law. 



If we were accurately acquainted with the constitution of the 

 earths, this law would be of great importance to the mineral- 

 ogist. It would enable him to distinguish between chemical 

 combinations and mechanical mixtures. I have no doubt that it 

 will ultimately throw a new light upon the chemical analysis of 

 minerals; even at present it may be applied with some success, 

 taking the imperfect knowledge that we have as a basis. 



8. When two combustible bases unite they always combine in 

 such a proportion that, when oxidized, either the quantity of 



