3^8 Mr. Keir’s Experiments and Obfervatlons on 
9. It appears then, that a folution of filver is not precipi- 
tated by iron in cold, unlefs it have a fuperabundance of phlo- 
gifticated acid 
10. Heat nffedts the action of a folution of fiver on iron: 
for if iron be digefted with heat, in a perfectly faturated folu- 
tion of filver, fuch as a folution of cryftals of nitre of filver 
in water, the filver will be deposited in its bright metallic 
ftate on different parts of the iron, and the iron which has 
been a£led on by the folution appears in form of a yellow 
ochre. 
1 1 . Bergman relates, that he has fometimes obferved 
beautiful cryftallizations or vegetations of metallic filver formed 
on pieces of iron immerfed long in a folution of filver. 
I have found that no time is able to effect this depofition, un- 
lefs the folution be in a ftate nearly fufficiently phlogifticated 
to admit of a precipitation by iron, but not completely phlo- 
gifticated enough to effiedt that purpofe immediately. 
12. Dilution with a great deal of water ieemed to difpofe 
the folutions of filver to be precipitated by iron more ealily. 
* It was faid, at § 4. that the addition of dephlogifticated nitrous acid to a 
faturated folution of filver did not render this folution precipitable by iron. 
Neverthelefs, as this acid diffolves iron, fuch a quantity may be added, as to 
overcome the counteracting quality of the folution of filver, fo that the acid 
fliall be able to a£t on the iron ; and while this metal is diifolving, it phlogifticates 
the mixture, which then becomes capable of being precipitated, and is in tact 
reduced to the fame Qircumftances as are defcribed at § 7. The limits of the 
quantities which produce changes cannot be aicertained, becauie they depend on 
the degrees of concentration and phlogifiication of the fubitances employed ; 
and therefore, whenever a change is faid to be produced by a certain fubiiance, it 
means that it may be produced by fome proportion, but does not imply by every 
proportion, of that fubiiance. Without attending to thefe confiderations, perfons 
trying to repeat the experiments mentioned in this Paper will be liable to be 
deceived. 
7 
A folution 
