90 M. Hess on the Scientific Labours of Richter. 



It is no longer a summit ; it is no longer to him that the che- 

 mist owes the compass without which he could not navigate. 

 Well, not only does Richter in his Stochiometrie, vol. iii. 

 p. 285, use this principle in order to verify the results of his 

 contemporaries, but even those of Wenzel are submitted to 

 this test. This, it may be objected, is not a proof, for he may 

 not have quoted the author from whom he has borrowed the 

 idea. But I have read and re-read Wenzel, and not a word, 

 not a trace of this idea is to be found in his work. It was 

 possible that an edition reprinted in 1800 might be inex- 

 act; I referred to that of 1782, and with the same result. 

 Here however is an unexceptionable proof that the principle 

 in question really belongs to Richter and not to Wenzel. 

 Open Wenzel's work, and you will find at the end a chap- 

 ter which is entitled " Applications of the laws of affinity 

 to particular cases" (Anwendung der Lehre von der Ver- 

 "joandtschqft der Korper auf besondere Falle). This is the 

 manner in which Wenzel expresses himself: "In chemistry, as 

 in every other natural science, the essential aim is to compare 

 recognised facts in their mutual relation, in order to deduce 

 other truths which are not perceived at first view. In the 

 experiments above quoted, we came to a knowledge of the 

 phaenomena which took place, by the fact of the union of two 

 substances. We saw in what order, under what condition, 

 and in what proportions they are combined. The greater part 

 however of these experiments, considered singly, are not of 

 great importance, whilst we only limit science to that. But 

 they acquire importance as soon as we apply them properly, 

 for their merit essentially depends upon a happy application." 



Let us follow Wenzel in his applications, and let us choose 

 for this purpose § 7. There he proposes as a question to find 

 the simplest and most advantageous manner of obtaining cry- 

 stallized verdigris. Here is what he proposes : — the sulphate 

 of copper and the acetate of lead are both soluble in water; 

 if these two solutions are mixed, the sulphuric acid by virtue 

 of its affinity for the oxide of lead will seize upon this and 

 form an insoluble substance, which may be utilized in the 

 arts on account of its whiteness. The liquid will contain 

 some acetate of copper which we separate from the precipi- 

 tate. Depending upon his analyses, Wenzel calculates the 

 quantity of oxide of lead contained in a given quantity of 

 acetate "of lead. He then calculates the quantity of sulphate 

 of copper necessary to precipitate all the oxide of lead. That 

 done, he examines the question, to learn whether the acetic 

 acid which the oxide of lead has just left is sufficient to dis- 

 solve all the oxide of copper which has just been left by the 



