84- M. Hess on the Scientific Labours of Richter. 



this question, and remained persuaded that the equivalent of 

 all bases belongs to an arithmetical progression, whilst the 

 numbers, which express the equivalents of the acids, form 

 geometrical progressions, the ratio of which is different ac- 

 cording to the different groups of acids. 



Now it is well established that facts do not support this no- 

 tion of Richter's: we shall therefore pass over this part of 

 his works, and I shall return to them but once, in order to 

 show how it was that his experiments were sometimes so 

 far from the truth as not to undeceive him. But if we go 

 back to the time when he lived, we shall feel that the question 

 raised was vast, and that if his undertaking was not crowned 

 with success, he at least deserves that these words should be 

 applied to him: 



" Quern si non tenuit, magnis tamen excidit ausis." 



Amongst the numerous subjects which Richter treats of in 

 the first volume, I shall only quote the method which he points 

 outforextractingplatinum from the ore of that metal ; foritis still 

 used. He recommends precipitating the solution of that metal 

 by sulphate of potash, to wash and dry the precipitate and to 

 decompose it by the carbonate of potash, so as to divest it 

 afterwards of all the salts by washing it with water. The 

 metal then remains brilliant as silver. The explanation of 

 the processes follows, which gives him an opportunity of 

 making some very important remarks. When we shall have 

 found, says he, numerical expressions for affinity, then these 

 seeming anomalies will disappear. Upon this occasion he 

 explains the difference between simple affinity and double af- 

 finity, and observes that it is nowhere proved that we can 

 really isolate a simple body, for, he says, each time that we 

 disengage an alkali or a metallic acid, if it be only carbonic 

 acid, heat must then be substituted for the acid ; lime is an 

 example of this. So it is with the acid from which we take a 

 base, it is combined with, or even neutralized by heat. In 

 the case of a simple affinity, we suppose but two elements, 

 whilst this shows you that there are at least three, for every 

 time that neutrality takes place, heat is substituted for the 

 third element. This is even the case when a metal is dissolved by 

 an acid and neutralizes it, for then it is the acid that furnishes 

 the heat, which becomes united with the other elements. 

 Richter therefore knew that bodies were pervaded by heat; 

 he urges the necessity of taking these phaenomena into con- 

 sideration, but he does not yet take a perfectly just view 

 of them; he believes that heat is just added to the elements, 

 when we know, on the contrary, that it has just been disen- 

 gaged. 



