340 I'HILOSOPHICAL TRANSACTIONS. [ANNO J/83. 



calces of any of the imperfect metals, and hence its use in cuppellation ; for 

 after it has lost its own phlogiston, it extracts that of the base metals, and thus 

 promotes their calcination and vitrification. 



Though the numbers in the second column express tolerably well the greater 

 or less affinity of metallic calces to phlogiston, yet they have this inconvenience, 

 that they are not homogeneous with those that express the affinities of acids to 

 other bases, which limits their use to a narrow compass, being, on that account, 

 incomparable with those that express the affinities of acids : I therefore endea- 

 voured to find a coincidence between them in some one instance, in order to re- 

 duce them to the same standard, as will be seen in the numbers in the 3d 

 column, which are homogeneous to those which express the affinities of acids to 

 their basis. 



The third point necessary for the explanation of the phenomena attending the 

 solution of metals, and their precipitation by each other, is to determine the 

 proportion of phlogiston which they lose by solution in each of the acids, and 

 the affinity which their calces bear to the part so lost. Mr. K. was not able to 

 determine this by any direct experiment ; for though he might determine the 

 part which escapes in the form of air, yet he could not that which is equally 

 separated from the metal, but retained in the solution ; yet from various collate- 

 ral considerations he made out the proportion of phlogiston probably separated 

 from the metals by the different acids. 



Of solutions in the vitriolic acid. — This acid dissolves iron and zinc, without 

 the assistance of heat ; because its affinity to their calces is greater than the 

 affinity which these calces bear to that portion of phlogiston which they must 

 lose before they can unite to the acid ; but all other metallic substances unite to 

 this acid only where it is concentrated and heated. 



Of solutions in the nitrous acid. — The nitrous acid has less affinity to all 

 metallic substances than either the vitriolic or marine. It has also less affinity 

 to them than they have to that portion of phlogiston which they must lose 

 before they can unite to it ; yet it dissolves them all (gold and platina excepted) 

 even without the aid of heat, because it unites itself to phlogiston unless too 

 dilute ; and the heat produced by its union with phlogiston is sufficient to pro- 

 mote the solution. 



Of solutions in the marine acid. — This acid is known to dephlogisticate metals 

 less than any other. Where the portion of phlogiston, necessary to be separated, 

 is more strongly attracted than the acid itself, it can operate no solution, or at 

 least very slowly, without the aid of heat ; nor even where the attraction of acid 

 is stronger to the calx than that of the portion of phlogiston it separates, it the 

 proportion of acid to such calx be very small ; because so small a quantity of acid 

 does not contain fire enough to volatilize the phlogiston ; and hence heat is 



