a66 jl/r. K.e i r’s Experiments and Obfervatiom on 
heat of the water-bath, calcine mercury into a white or greyiflt 
powder. Nickel was alfo partly calcined and partly diflblved by 
thefe mixtures. I did not perceive that any other metal was 
affe&ed by them, excepting that the furfaces of fome of them 
were tarnifhed. 
1 6. Thefe mixtures of oil of vitriol and nitre were apt 
to congeal by cold, thofe efpecially which had a large propor- 
tion of nitre. Thus, a mixture of 1000 grain-meafures of oil 
of vitriol and 480 grains of nitre, after having kept fluid 
feveral days, in a phial not fo accurately flopped as to prevent 
altogether the efcape of fome white fumes-, congealed 
at the temperature of 55 ° of Fahrenheit’s thermometer ; 
whereas fome of the fame liquid, having been mixed with equal 
parts of oil of vitriol, did not congeal with a lefs cold than 45 . 
The congelation is promoted by expofure to air, by whiclv 
white fumes rife, and moifture may be abforbed, or by any 
other mode of flight dilution with water. 
17, Dilution of this compound acid, with more or le a 
water, alters confiderably its properties, with regard to its 
aftion on metals. Thus it has been obferved, that in its concen- 
trated ftate it does not aft on «! but, by adding water, it 
acquires a power of afting on that metal, and with different 
effect, according to the proportion of the water added. Thus, 
by adding to two meafures of the compound acid one meafure 
of water, the liquor is rendered capable of calcining iron, an 
forming with it a white powder, but without effervefcence. 
'With an equal meafure of water effervefcence was produced. 
With a larger proportion of water the iron gave alfo a brown 
colour to the liquor, fuch as phlogifticated nitrous acid acquires 
from iron, or communicates to a folution of martial vitriol in 
water. 
18. Dilution 
