6q6 philosophical transactions. [anno 1790. 



we have only the choice of terms between words derived from the ancient theory, 

 and those which have been lately proposed by the opposers of that theory. In 

 this dilemma I have preferred the use of the former, not that I wish to show 

 any predilection to either theory, but because that system, having long been 

 generally adopted, is understood by all parties; and principally because, by using 

 the words of the old theory, I am at liberty to define them, and to give signi- 

 fications expressive merely of facts, and of the actual state of bodies; whereas 

 the language and theory of the antiphlogistic chemists being interwoven and 

 adapted to each other, the former cannot be divested of its theoretical reference, 

 and therefore seems inapplicable to the mere exposition of facts, but ought to 

 be reserved solely for the explanation of the doctrines from which this language 

 is derived. Thus, by the definition before mentioned of phlogistication, this 

 word expresses not the presence or existence of an hypothetical principle of in- 

 flammability ; but a certain well-known quality of acids and of other bodies, 

 communicated to them by the addition of many actual inflammable substances. 

 Thus nitrous acid acquires a phlogisticated quality by addition of a little spirit of 

 wine, or by distillation with any inflammable substance. 



3. No two substances are more frequently in the hands of chemists and artists 

 than vitriolic acid and nitre, yet I have found, that a mere mixture of these, 

 when much concentrated, possesses properties which neither the vitriolic acid 

 nor the nitrous, of the same degree of concentration, have singly, and which 

 could not easily be deduced, k priori, by reasoning from our present knowledge 

 of the theory of chemistry. 



4. Having found by some previous trials that a mixture composed of nitre dis- 

 solved in oil of vitriol was capable of dissolving silver easily and copiously, while 

 it did not affect copper, iron, lead, regulus of cobalt, gold, and platina, I con- 

 ceived, that it might be useful in some cases of the parting of silver from copper 

 and the other metals above mentioned; and having also observed, that the dis- 

 solving powers of the mixture of vitriolic and nitrous acids varied greatly in 

 difi^erent degrees of concentration and phlogistication, I thought that an investi- 

 gation of these effects might be a subject fit for philosophical chemistry, and 

 might tend to illustrate the theory of the dissolution of metals in acids. With 

 these views I made the following experiments. 



5. I put into a long-necked retort, the contents of which, including the neck, 

 were 1400 grain measures, 100 grain measures of oil of vitriol of the usual 

 density at which it is prepared in England, that is, whose specific gravity is to 

 that of water as 1.844 to 1, and 100 grs. of pure and clean nitre, which was 

 then dissolved in the acid by the heat of a water- bath. To this mixture 100 grs. 

 of standard silver were added; the retort was set in a water bath, in which the 

 water was made to boil, and a pneumatic apparatus was applied to catch any air 



