3 28 Dr. Priestley’s Experiments and Obfervations on 
fumes during the folution. By adding a folution of melted 
nitre to the blue folutions of copper either in the nitrous or 
■^vitriolic acids, the phlogifticated acid of the melted nitre im- 
mediately communicates a green colour. The marine acid 
tends more than the other acids to give a green colour ; but I 
am inclined to impute the colour of yoitr liquor principally to 
the phlogiflication of the acid, becaufe upon adding a very 
fmall portion of vitriolic, marine, or nitrous acid, the colour 
was immediately changed to a light blue. The folution of 
filver, being purpofely acid, always produced this change of 
• colour, and I therefore confidered, that the phlogifticated acid 
was expelled in the operation, and could not affedl the preci- 
pitation. 
Experiments have taught me, that an exceedingly flight de- 
gree of that quality which is called the phlogiflication of nitre, 
is fufficient to produce an alteration in the colour of folutions 
<of copper, and that the colour will be changed when the de- 
gree of phlogiflication is incapable of producing any precipi- 
tation of filver. Not only a folution of melted nitre will 
always change the colour of cupreous folutions, but even cry- 
stals of nitre, when mixed with the nitrous acid, and the 
mixture boiled to drynefs upon copper, and re-diflolved in 
water, will give a green folution. If cryftals of nitre be dif- 
folved in a colourlefs folution of filver in nitrous acid, and this 
mixture added to a folution of copper in the fame acid, the 
blue colour of the latter will be changed to a green, although 
neither the nitre nor folution of filver will feparately have this 
effect, neither will nitre diflolved in a dilute nitrous acid. I 
do not know what degree of phlogiflication may be required to 
precipitate filver, but i fuppofe it to be very great; at leaft it is 
certain, that the degree of phlogiflication capable of giving a 
green 
