on the Calcination of Metals. 77 



because the reason which he assigns for the increased weight of 

 the calces of lead and tin, has an immediate relation with that, 

 which is on the point of being acknowledged by all chemists. 



It was not, Monsieur, till after I had published in your jour- 

 nal, the second part of my experiments on the calces of mercury, 

 that I became acquainted with Key's book. I could not men- 

 tion it in the very short enumeration I then gave of tlie different 

 opinions on the cause of the increased weight of metallic calces ; 

 my fault, involuntary as it was, must be repaired, and to this 

 end, I hasten to do justice to an author, who, by the profound- 

 ness of his speculations, has succeeded in assigning the true 

 cause of that increase. 



I hope, Monsieur, that you will concur with me, in making 

 known Key's excellent work. Your journal is read tln-oughout 

 France, it is spread over foreign countries ; if you would insert 

 this notice in it, the chemists of all countries would soon know, 

 that it was a Frenchman, who by the power of his genius and 

 reflections, first guessed the cause of the increased weight that 

 certain metals experience when converted into calces, by ex- 

 posure to the action of fire, and that it is precisely the same as 

 that, whose truth has just been proved by the experiments which 

 M. Lavoisier read at the last public sitting of the academy of 

 sciences. 



P. S. We may presume, that copies of Key's work are rare. 

 That which I have before me belongs to M. de Villiers, physi- 

 cian of the faculty of Paris, who has the best chemical library 

 in France, and which he has sincere pleasure in laying open to 

 the cultivators of the science. M. de ViUiers's copy came from 

 the library of the late M. Villars, physician at Rochelle, which 

 was sold by his heirs in the course of last year. This copy was 

 defective, it ended at p. 142, containing only the beginning of 

 the 28th Essay. I requested M. Capperonie\ to allow me to 

 transcribe, from the copy in the king's library, the two pao-cs 

 that are wanting in M. de ViUiers's, — which he had the goodness 

 to accede to. Thus, they who may wish to read John Key's work, 

 are informed, that there is a copy of it in the king's library, at 

 the end of which they will find two manuscript letters ; the first 



