566 PHILOSOPHICAL TRANSACTIONS. [aNNO l/QS. 



The long continuance of the late frost havuig afforded me opportunities of 

 repeating these experiments in various ways, I shall mention briefly the result of 

 such as appear to me to be material. 



I have found that quicksilver may be frozen by cooling the nitrous acid only, 

 saving the trouble and inconvenience of cooling the snow also, either by adding 

 snow at -|- 32°, to nitrous acid at — 29° ; or snow at + 25°, to nitrous acid at 

 — 20° ; or snow at + 20° to nitrous acid at — 12° ; most winters offer an op- 

 portunity of doing it in this way ; the nitrous acid may be cooled in a mixture 

 of snow and nitrous acid : that it may also be frozen, by mixing expeditiously 

 together snow and nitrous acid, when the temperature of each is -f- 7° : or by 

 mixing ground ice and nitrous acid at + 10°- Hence it follows, that the cold 

 of this climate offers occasionally opportunities of freezing quicksilver, without 

 previously cooling by art the materials to be mixed ; for I have once seen the 

 thermometer at + 6°, and others I believe have seen it lower. 



I expected an opportunity would have offered this winter, but the lowest point 

 I saw my thermometer at, this season, was only + 10° ; at this temperature, I 

 mixed nitrous acid (cooled out of doors to the temperature of the air) and snow 

 on Jan. 23d last ; but the cold produced was not quite sufficient to freeze the 

 quicksilver, though very near it, as indicated by a thermometer. From what I 

 have observed since these latter experiments were made, I think it may be rea- 

 sonably expected, that powdered ice and nitrous acid at + 14°, or snow at -j- 10°, 

 will succeed, if mixed expeditiously. Strong spirit of vitriol, of the specific gra- 

 vity 1.848, required to be diluted with half its weight of water, and produced 

 with snow at the temperature of -f 30°, about 8 degrees less than with nitrous 

 acid, sinking the thermometer to — 24°; 4 parts of the diluted vitriolic acid re- 

 quired, at that temperature, 6 parts of snow. 



It perhaps will be remarked, that I have taken no notice before of the vitriolic 

 acid. The reason is, because the freezing point of quicksilver being 39°, it may 

 be frozen tolerably hard by a mixture of nitrous acid with snow, or ground ice, 

 though the utmost degree of cold this acid can produce with snow is — 46° ; 

 which degree of cold may be produced by mixing the snow or ground ice and 

 nitrous acid at 0°. If it be required to make it perfectly solid and hard, a mix- 

 ture of equal parts of the diluted vitriolic acid and nitrous acid should be used 

 with the powdered ice, but then the materials should not be less than — 10° be- 

 fore mixing. If a still greater could be required than a mixture of this kind 

 can give, which is about — 56', the diluted vitriolic acid alone should be used 

 with snow or powdered ice, and the temperature at which the materials are to be 

 mixed not less than — 20°. Select, according to the intention, either of the 3 

 following mixtures : First, snow or pounded ice 2 parts, and common salt 1 

 part, which produces a cold of — 5° : 2d, snow or pounded ice 12 parts, common 



