[ 36i ] 
giving a flight tinge of the purple, when mixed 
with galls : but none of thofe earths are any longer 
detained in the water, than while it continues im- 
pregnated with fome mephitic air j when this air is 
entirely ieparated from the water, it is wholly de- 
compounded, having loft its diftinguifhing brifk and 
pungent tafte, and its power of ftriking a purple co- 
lour with galls ; its more volatile and elaftic prin- 
ciples being exhaled, its metalline and abforbent 
earths then fublide in a white flocculent fediment, 
and no other fubftance remains diffolved in the water, 
fave only the fmall portion of alkaline and neutral 
falts, which enter its compofition. 
From this fhort recapitulation of the above-men- 
tioned experiments, it therefore appears, that the 
pouhon water undergoes a decompofition, when 
its air is expelled from it by means of heat. The 
oppofite extreme of cold is alfo found to produce the 
fame effedt of decompounding the poui-ion water, 
when this its aereal principle is expelled from it by 
means of congelation. 
For having poured fome of this water into 
open tin veffeis, that were placed in the com- 
mon freezing mixture of fea-falt and fnow, fo foon 
as the water began to fhoot into ice at the bottom 
and fides of the veffeis, very minute bubbles of air 
inceffantly arofe therein, and were difcharged from 
its iurface with fuch force, as to carry with them 
fmall particles of the water to a conliderable height ; 
and continued thus to fly off, till all the water was 
congealed. The ice was very white, from the mi- 
nute bubbles of air, which were every where inter- 
fperfed though it, and by which the frozen water 
Vol, JLXiVk Aaa <con- 
