M. Hess on the Scientific Labours o^ Richter. 91 



sulphuric acid, and always starting from his analyses, he comes 

 to the conclusion that the acetic acid set at liberty is not suf- 

 ficient to dissolve all the oxide of copper, and that for the 

 quantity of copper employed, which is 124 parts, there will 

 be found of it 9j parts mixed with the sulphate of lead as an 

 oxide. In this case Richter, starting from his principle, would 

 necessarily say, these analyses are false ! as he did in many 

 cases. What does Wenzel ? he, on the contrary, concludes 

 that after having separated the solution from the precipitate, 

 this last must be treated with a little sulphuric acid to remove 

 the oxide of copper. Here then is a very evident proof that 

 Wenzel did not even suspect a similar relation to that which 

 was discovered by Richter. Richter not merely discovers 

 this principle, but he comprehends it in its totality; he follows 

 it in all its consequences, and nothing can show us more fully 

 the depths of his convictions with respect to this, than some 

 words which are to be found in the preface to the 10th volume. 

 " The theorems of stcechiometry," says he, " contain a neces- 

 sity; they may be constructed and have the value of a -priori 

 principles." 



These principles conduct him to new generalities. He finds 

 that when a metal is precipitated from its solution by another 

 metal, the quantities of oxygen necessary to preserve equal 

 quantities of the two metals in solution, are to each other in 

 the inverse ratio of the masses of the two metals. Further 

 oh, he concludes, since when several metals are precipitated 

 from solution by one another, the solution always remains 

 neutral, it is sufficient to know the difference of weight be- 

 tween one of these metals and its oxide, to deduce from it the 

 quantity of oxygen which all the others contain in the state 

 of oxide. For this it is sufficient to take a constant quantity 

 of the same acid, for then all the metals that may be dissolved 

 in this acid will contain the same quantity of oxygen, which 

 will then only have to be deducted from the weight of the 

 oxide, in order to obtain that of the metal. 



Richter takes sulphuric acid for a starting-point, and pre- 

 pares a table of the composition of the metallic sulphates ; in 

 this table the quantity of oxygen of the metal being necessarily 

 constant, he designates it by the letter U. This is what we 

 now designate by the letter O. Richter was then very near 

 establishing a system of equivalents, just like that which is at 

 present used ; for that object it was sufficient to refer all the 

 numbers to this constant quantity U. But this simple idea had 

 not struck him, for in another column he gives the composition 

 of the muriates, takingjlOOO parts of muriatic acid as a starting- 

 point ; in another column, indeed, he gives the composition of 



