^6 Mr . kir wan’s Experiments, and Obferv aliens on 
triturated together, the lhaell of the volatile alkali will imme- 
diately be perceived * ; or if, inhead of iron, minium, or diapho- 
retic antimony, or zinc, be ufed, that fmell is perceived as 
foon as they are mixed, 9 Mem. Scav. Etrang. p. 575. monnet, 
DilT. Met. 209. But it will naturally be alked, how then it 
happens, that all metallic folutions are precipitated by alkalies 
and earths ? The anfwer is eafy ; all metallic falts are held in 
folution by an excefs of acid. If alkalies and earths did nothing 
more than abforb this excefs of acid, a precipitation ought 
to take place ; but they do hill more, for they take up the 
greater part even of the proportion of acid neceflary to faturate 
the metallic earth, and this they are enabled to do by means of 
a double affinity ; for during the folution of metals, only a 
comparatively fmall part of the phlogihon efcapes out of the 
folution, the remainder is retained by the compound of acid 
and calx : when, therefore, an alkali or earth is added to fucli 
a folution, the phlogihon quits the acid, and re-combines with 
the calx, while the greater part of the acid unites to the preci- 
pitant. Notwithftanding this great affinity of metallic earths 
to acids, falts, whole balls is a fixed alkali or earth, are in few 
inftances decompofed by metals or their calces, by reafon of 
the inability of the acids while combined with thefe bahs, and 
thereby deprived of a great part of their fpecific fire, to volati- 
lize the phlogihon combined with the metallic earths, which 
muh neceffarily be expelled before an acid can combine with 
them. And as to metallic calces, they are generally combined 
with fixed air, which alfo muh be in part expelled. 
But ammoniacal falts, containing much more fire (for they 
abforb fire during their formation) for that reafon acl much 
more powerfully on metals. Allowing then the affinity of the 
* MONNET, Diflbl. Met. 7 I. 
6 
mineral 
