the Attractive Powers of Mineral Acids, 73 
law ditbovered by Dr. crawford, by the union of phlogifton 
to the acid, for metallic calces produce no heat. As to mer- 
cury, the obfervation is not exa£t, for its folution is accompanied 
with heat, as Mr. Lavoisier has obferved, 1 lavois. 248. 
Of folut ions in the marine acid. 
This acid is known to dephlogifticate metals lefs than any 
other. Where the portion of phlogifton, neceflary to be fepa- 
rated, is more ftrongly attra&ed than the acid itfelf, it can 
operate no folution, or at leaf: very flowlv, without the aid 
ot heat ; nor even where the attraction of acid is ftronger to 
the calx than that of the portion of phlogifton it feparates, if 
the proportion of acid to fuch calx be very fmall ; becaufe fo 
fmall a quantity of acid does not contain fire enough to volati- 
lize the phlogifton ; and hence heat is neceflary for the folution 
of lead in this acid. The dephlogifticated acid a£ts more 
powerfully. 
Of precipitations of and by iron. 
The mutual precipitations of iron and copper from the 
vitriolic acid by each other, have been well explained in a ge- 
neral manner by Mr. monnet and Mr. bergman ; I fhall here 
Ihevv the reafon of tliefe precipitations more diftinbtiy. 
If a piece of copper be put into a faturate folution of iron, 
frefti made, no precipitation will happen, nor will any of the 
copper be difl'olved in twelve hours, nor even in a longer time, 
if the accefs of air to the folution be prevented ; but if the 
folution be expofed to the open air, the addition of a volatile 
alkali will ftiew the copper to have been abted upon in 24 
hours, or fooner if heat be applied, and a calx of iron is pre- 
cipitated. The operation of the affinities in the fir ft cafe is as* 
follows. 
Vol. LXXIII. 
L 
Quiefcent. 
