3 jo Mr. Keir’s Experiments and Obfervations on 
properties with regard to its aftion on metals from the acid de- 
ferred in the firft feftion. It has been obferved, that the 
latter compound has little aftion on any metals but filver, tin, 
mercury, and nickel. On the other hand, the phlogifticated 
compound not only a£s on thefe, but alfo on feveral others. 
It forms with iron a beautiful rofe-coloured folution, without 
application of any artificial heat ; and in time a rofe-coloured 
faline precipitate is depofited, which is foluble in water with 
con fide rable effervefceuce. It diflblves copper, and acquires 
from this metal, and alfo from regulus of cobalt, zinc, and 
lead, pretty deep violet tinges. Bifmuth and regulus of anti- 
mony were alfo attacked by this phlogifticated acid. 
To afcertain more exaffly the effects of this phlogifticated 
acid on fome metals, I made the following experiments, with 
a liquor prepared by making nitrous gas pafs through oil of 
vitriol during a confiderable time. 
22. To 200 grain-meafures of the oil of vitriol impregnated 
with nitrous gas, put into a retort with a long neck, the capa- 
city of which, including the neck, was 1150 grain-meafures, I 
added 144 grains of ftaudard filver, and immerfed the mouth 
of the retort in water, under an inverted jar filled with water, 
to catch the gas which might be extricated. 
The acid began to difiblve the filver with effervefcence by 
application of heat ; the folution became of a violet colour, 
and the quantity of nitrous gas received in the inverted jar was 
J47 oo grain-meafures. Upon weighing the filver remaining, 
the quantity which had been dilfolved was found to be 70 
grains. When water was added to the folution, an effer- 
vefcence appeared, but only a very fmall quantity of gas w^ 
extricated. By means of the water, a white faline powder 0^ 
filver, foluble in a larger quantity of water, was precipitated 
from 
