the Production of artificial Cold. 133 
forced into the cup of the lower vessel, and stirred about in it a 
little. 7th. The upper vessel being removed, and set aside, the 
muriate of lime and ice are to be thoroughly mixed, and a 
small tube, containing the quicksilver to be frozen, stirred about 
in the mixture ; or the bulb of a spirit-thermometer, to take 
its temperature, which, if the experiment be conducted pro- 
perly, will indicate, even if the experiment be made in summer, 
a cold of —50°* 
The apparatus, as represented in the drawing, is upon as fit 
a scale as may be required for common experiments; by 
attention, however, to the proportions given, one of any size 
may be procured. 
Muriate of lime produces no effect upon tin or japanned 
vessels ; hence the apparatus is best made of common block-tin ; 
observing that the tube and cup be made of the thinnest tinned 
iron, and the whole besides of the same substance, but con- 
siderably thicker ,-f- 
* Muriate of lime and ice-powder, mixed at the temperature of -f- 20°, give a cold 
of — 48* ; if mixed at 4- 15, of — 5 1° ; and, at -f io®, a cold of — 54°. 
The freezing point of quicksilver is — 39° but that metal requires a temperature 
of — - 45°, to assume its perfectly solid state. 
I have repeatedly frozen quicksilver in the middle of summer, by mixing together 
muriate of lime and ice-powder, at -f- 20° ; and likewise, by mixing together nitrous 
acid and ice-powder, at -J- 8°. 
+ The best method of constructing vessels for the purpose of excluding heat, is 
obviously to have them made of the best non-conducting substance, lined within with 
the best conducting substance ; hence these vessels (the tubes excepted) might be. 
fitter for the purpose, if made of wood lined with tin. 
My general rule for constructing the apparatus, is to allow four times, by measure, 
the water to be frozen and reduced to powder, in the capacity of the tube that is to 
contain it ; and three times the weight (by measure) of the muriate of lime, to the 
cup in which the muriate of lime is to be cooled, and the ice-powder afterwards added 
