Acidity, Decompofuion of Water, and Fhlogifton. 329 
green colour to folutions of copper is infufficient to precipitate 
filver. Mr. Cavendish, when he relates the fad of the pre- 
cipitation of filver, fpeaks only of nitre, much phlogifticated, 
pofl'cfling this property. 
To obviate any fufpicion of the precipitation of filver being 
owing to the phlogiftication of the acid, I added to fome of 
the green liquor about an equal quantity of colourlefs nitrous 
acid and fome difcilled water, and I kept this mixture boiling 
half an hour, in order to difengage and expel any phlogifticated 
acid which it might contain. To the liquor, which remained 
perfedly pellucid, I added a folution of filver, upon which the 
precipitation immediately took place with all its ufual circum- • 
fiances, and in as great a degree as before. 
If, upon examining the acids which you or others may 
hereafter obtain by the inflammation of airs, a mixture of 
marine acid oe conftantly found to accompany the produdion 
of the nitrous, the fad will be only analogous to all the other 
known produdions of nitrous acid; in all which, either in 
the natural formation of nitre as in Spain and India, or in the 
nitre beds and walls made by art, a very large proportion of 
marine halts is conftantly obferved to accompany the nitre. 
I fhall conclude my letter with mentioning a fad, which I 
obferved in making fome experiments to find the came of the 
formation of the green powder above-mentioned, and which, 
though not relative to the prefent fubjed, may be thought not 
unworthy of communication. It is the desompofition of common- 
fait and feparation of its alkali by copper. As I conceived the opinion 
that the formation of this green powder by evaporation of this 
green liquor was owing to the perfed faturation of the acid, 
among other modes of obtaining a perfedly faturated folution 
of copper, I fp tinkled upon plates of copper ftrong folutions - 
of. 
