124 
Mr. Walker's Experiments on 
(which happened when the liquor had been evaporated to the 
consistence of a thin syrup,) and then reduced to fine powder. 
From the preceding account it is apparent, that Pr. Lowitz 
has discovered a single frigorific mixture, by which quicksilver 
may be frozen whenever the temperature of the materials at 
mixing is no colder than -f- 3 2 ° 5 whereas, the nitrous acid with 
snow, which has hitherto been considered as the most powerful 
of frigorific mixtures, requires a temperature of -j- 7 0 , to pro- 
duce the same effect. 
At the same time, however, it should be observed, that an ex- 
periment with this salt, prepared as above, can be made only 
during a freezing atmosphere ; the salt itself thus prepared, 
becoming, as may be inferred from the above, and as I have 
myself experienced, unfit for use by a warmer temperature. 
Reflecting upon my former experiments, I determined to try 
the effect of this salt, reduced to such a strength, by evapora- 
tion, as to endure being kept, in a solid state, throughout the 
year. For this purpose, I found it necessary that the liquor, pre- 
pared as before, should be evaporated to the consistence of a 
thickish syrup, before it is set by to crystallize ; when the pro- 
duce will be a semi-transparent, uniform, crystalline mass, 
which affords, on pulverizing, a white pearl-coloured powder, 
which should be preserved for use in a bottle closed with a 
ground stopper. 
Some of the powder above mentioned, (which had been pre- 
viously subjected to a temperature of 70°, without melting,) 
I mixed with snow, each at the temperature of -f 32 0 ; when 
the thermometer, to my perfect satisfaction, sunk to — 40° ; 
and, at another time, when the air was -j- 20°, I froze quick- 
silver perfectly solid, by a mixture of the same materials. 
