1813.] Definite Proportions in Chemical Combinations. 39 



is 10 the quantity necessary to saturate 100 parts of silver as the 

 miinber 4-16 to 7'9- This law w; :• first pointed out by Gay- 

 Lussac* It may be expiessed in the following manner, which 

 adapts it better to the purposes of the chemist. When different 

 metallic oxides saturate the same weight of acid, each contains 

 exactly the same weight of oxvgen. According to Berzelius, in 

 order to saturate 100 parts of muriatic acid, a metal must be 

 combined with 42 parts of oxygen ; to saturate 100 of sulphuric 

 acid, it must be combined with 20 parts of oxygen. 



I believe that this law applies only to those metals which are 

 precipitated by each other ; namely, gold, silver, mercury, 

 copper, lead, cobalt, and perhaps iron, zinc, and one or two 

 others. The other metals, I conceive, follow a different law ; 

 and it is because they follow a different law that they are not 

 precipitated. This will appear more obviously hereafter, when 

 we come to examine the constitution of the metallic salts. 



3. When sulphur combines with a metal, the proportion 

 remains unchanged, though the sulphur be converted into an 

 acid, and the metal into an oxide. Thus the proportion of 

 metal and sulphur in sulphate of copper is the same as in sul- 

 phuret of copper. Hence sulphuret of lead, when treated with 

 nitric acid, is converted into neutral sulphate of lead, sulphuret 

 of antimony into sulphate of antimony, and so on. This law, 

 which is of great importance in practical chemistry, and very 

 much facilitates the analysis of the metalline salts, was first 

 pointed out by Berzelius. 



4. The oxygen in a metallic protoxide is equal to half the 

 sulphur in the sulphuret of the same metal, supposing the 

 weight of the metal in both cases 100. This canon was first 

 specified by Berzelius. It depends obviously upon the fact above 

 established, that an atom of sulphur is twice the weight of an 

 atom of oxygen, and holds only in those cases where the prot- 

 oxide is a compound of one atom of metal and one atom of 

 oxygen; and the sulphuret, of one atom of metal and one atom 

 of sulphur. It may hold also when the oxide contains two atoms 

 of oxygen, and the sulphuret two atoms of sulphur. This is the 

 CMC with the black oxide of iron and magnetic pyrites. Hence 

 the canon is of some utility, by enabling us the better to deter- 

 mine the constitution of the sulphuretsj which, like the oxides, 

 are susceptible of considerable) variation. 



5. In combinations of two bodies containing each a quantity 

 of oxygen, the weight of oxygen in each body is either equal, or 

 one contains twice, thrice, four times, <^c as far as eight times, 

 the quantity of oxygen in the other. This law has been laid down 

 by Berzeliusjf but I must acknowledge I entertain considerable. 



' Mrui. d' ArtueiJ, ii, J 57. t Aon. dc Chim. Ixvxiii. 119. 



6 



