, Mr. Keir’s Experiments and Obfervations on 
. - . 
6 . That this phlogiftication was found to communicate to 
the mixture the power of diffolving, though in fmall quanti- 
ties, copper, iron, zinc, and regulus of cobalt. 
7 . That water expels from a highly phlogifticated mixture of 
concentrated vitriolic and nitrous acids, or of oil of vitriol 
impregnated with nitrous gas, a great part of its contained 
gas ; and that therefore this gas is not capable of being re- 
tained in fuch quantity by dilute as by concentrated acids. 
Water unites with the mixture of oil of vitriol and nitre, 
without any confiderable effervefcence. 
20. To thefe obfervations I fhall fubjoin one other fact, 
namely, that, when to the mixture of oil of vitriol with nitre 
a faturated folution of common fait in water is added, a power- 
ful aqua regis is produced, capable of diffolving gold and pla- 
tina ; and this aqua regis, though compofed of liquors perfectly 
colourlefs and free from all metallic matter, acquires at once a 
bright and deep yellow colour. The addition of urv common 
fait to the concentrated mixtures of vitriolic and nitrous acids 
produces an effervefcence, but not the yellow colour ; for the 
production of which therefore a certain proportion of water 
leems to be neceffary. 
PART II. 
On the precipitation of filver from nitrous acid by iron. 
SECTION i. 
i. Bergman relates, that upon adding iron to a folution of 
filver in the nitrous acid no precipitation enfued * ; although 
* Differt. de Phlog. quantitate in Metallis, 
the 
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