206 Dr. Macneven's Exposition of [Sept. 



quantity of acid necessaiy to saturate 100 parts of mercury is to 

 the quantity necessary to saturate 100 parts of silver as the 

 number 4-16 to 7-9. This law was first pointed out by Gay- 

 Lussac. Dr. Thomson expresses it in the following manner, 

 the better to adapt it to the purposes of the chemist : " When 

 different metallic oxides saturate the same weight of acid, each 

 contains exactly the same weight of oxygen." 



According to Berzelius, in order to saturate 100 parts muriatic 

 acid, any metal whatever must be combined with 42 parts of 

 oxygen. To saturate 100 parts of sulphuric acid, any metal 

 whatever must be combined with 20 parts of oxygen. 



This law necessarily implies that when an acid unites to a 

 base, the oxygen in the acid is always a multiple of the oxygen 

 in the base by a whole number ; and generally by the number 

 denoting the atoms of oxygen in the acid. Thus, sulphuric acid 

 is composed of 1 atom sulphur = 16, and 3 atoms oxygen = 

 24, and 100 parts of sulphuric acid containing 60 oxygen (24 : 

 16 :: 60 : 40) will combine Avith and saturate a quantity of base 

 which contains 20 oxygen. Now, 20, the oxygen in the base, 

 multiplied by 3, the number of atoms in sulphuric acid, makes 

 60, the quantity of oxygen in 100 parts of sulphuric acid. 



28. 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 ; for the protosulphuret of copper is composed 

 of 1 atom sulphur + 1 atom copper ; and the sulphate of the 

 protoxide of copper is composed of 



1 atom sulphur + 3 atoms oxygen (acid) 



1 atom copper + 1 atom oxygen (protoxide or base.) 



in which the sulphur and copper do not vary. 



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. 



29. 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 to be the same. This canon was first 

 specified by Berzelius. It depends on the fact that an atom of 

 sulphur is twice the weight of an atom of oxygen ; and it is 

 limited to those cases where the protoxide is a compound of 

 1 atom of metal and 1 atom of oxygen ; and the sulphuret of 

 1 atom of metal and 1 atom of sulphur. This canon enables us 

 to determine the constitution of the sulphurets by means of the 

 oxides, and vice versa. 



30. In combinations of two bodies, each containing a quantity 

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

 one contains twice, thrice, four times, &.c. as far as eight times 



