' Mr. Walker's Observations, &e. 271 
cxpence of materials in collecting a sufficient quantity, deter- 
mined me to relinquish this mode for another, by which I can 
easily and expeditiously procure ice in the fittest form for ex- 
periments of this kind ; the method I mean, is by first freez- 
ing water in a tube, and afterwards grinding it into very fine 
powder. Thus possessed of the power of making ice, and af- 
terwards reducing it to a kind of snow, the congelation of 
quicksilver becomes a very easy and certain process ; for by 
the use of a very simple apparatus (Tab.XXIII. fig. 1.) quick- 
silver may be frozen perfectly solid, in a few minutes, where- 
ever the temperature of the air does not exceed 85°, thus : one 
ounce of nitrous acid is to be poured into the tube b of the 
vessel, observing not to wet the side of the tube above with it; 
a circular piece of writing paper of a proper size is to be 
placed over the acid, resting upon the shoulder of the tube, 
and the paper brushed over with some melted white wax; 
thus prepared, the vessel is to be inverted, and filled with a 
mixture of diluted nitrous acid, phosphorated soda, and nitrous 
ammoniac, in proper proportions for this * temperature, and 
tied over securely, first with waxed paper, and upon that a 
wet bladder. 
The vessel being then turned upright, and placed in a shal- 
low vessel, viz. a saucer or plate, an ounce and a half of rain 
or distilled water is to be poured into the tube, which is to be 
covered with a stopper or cork, and, as soon as frozen solid, 
ground to very fine powder, an assistant holding it firmly 
and steadily the while ; observing occasionally to work the 
instrument in different directions up and down, that no lumps 
* 1 have, by a very accurate preparation of this mixture, sunk a thermometer from 
85° (temperature of the vessel and materials) to -f- z°. 
N 11 2 
