Tramlation of Rey's Essays. 279 



fixed part remains at the bottom of the furnace in the state of 

 cinder, containing the fixed salt, which is separated by washing, 

 and the volatile part rises all round the vessel, containing in a 

 superfluous humidity (derived from the vegetable) a volatile 

 salt, of a metallic nature ; which, raised on high on the wings 

 of the humidity, meeting the air directly over the vessel, which 

 is more rarefied and lighter than the vapour of the charcoal, 

 sinks through it into the vessel and attaches itself by a close 

 sympathy to the fixed salt of the calx of tin, which having 

 received a certain quantity of it, and being as it were saturated, 

 rejects the surplus ; like as salt of tartar, after a certain number 

 of cohobations, cannot be further impregnated by the volatile 

 salt, contained in the aqua vitse. Having run over his writing, 

 I refuted this opinion in his presence by the following argu- 

 ments. Since we must give every one credit in his own art, if 

 we have nothing to the contrary, it is reasonable, in speaking 

 of volatile salts, to borrow the language of the alchymists, who 

 alone can discourse of it in a proper manner, having first dis- 

 covered it and revealed it to us, when we were not aware that 

 there was a volatile salt in nature. They found in vegetables, 

 as in almost every thing, two sorts of salts, one fixed, the 

 other volatile ; the former containing a fixed spirit in itself, and 

 being contained in the solid part of its subject ; the latter con- 

 taining a volatile spirit, and being contained in the juices. 

 The fixed is obtained, say they, by calcination, lemaining after 

 it in the ashes. The other cannot sustain the fire, being no 

 less volatile in effect than in name, and thus rises with the 

 slightest heat with the juice that contains it, or is lost even by 

 simply drying the vegetable. Now this being so, it is out 

 of doubt, that in the whole of the charcoal there can be no 

 volatile salt, for even the wood of which it is made cannot 

 contain any, since it is previously dried ; and even if it did con- 

 tain any, who but sees it must of necessity lose it, when in the 

 charring it becomes a burning coal? Truly, were I to grant this 

 favour, and allow that charcoal contains volatile salt, they 

 who know how rare it is in every thing, will never believe that 

 from the small quantity of charcoal which the Sieur Brun used 



