I06 PHILOSOPHICAL TRANSACTIONS. [aNNO J 786. 



the temperature of the air being — Sl**-^, but that of the liquor was not tried. 

 As this congelation must have been of the aqueous kind, and seems to have 

 taken place at the temperature of — 5l\, it should follow, that this acid had 

 no power of dissolving snow in a cold of 51°4. ; so that it does not at first ap- 

 •pear why a cold 4° greater than that should have been produced in the foregoing 

 experiment. The reason is, that at the time the mixture arrived at -— 55°-i-, it 

 appeared by the diminution of its fluidity to have contained some undissolved 

 snow, and some more was added to it after that time, which before the first of 

 January dissolved and mixed with the acid ; so that the acid in the mixture, at 

 the time it sunk to — 55%, was not quite so much diluted as that which froze 

 on January 1. This is the reverse of what happened in the trial of the nitrous 

 acid ; as in that experiment the fluid part, at the time of the greatest cold, was 

 weaker than the whole mixture together ; but it must be considered, that that 

 mixture contained much congealed acid, as well as undissolved snow, whereas 

 this contained only the latter. 



Jan. 1, snow was added to the other half of the acid diluted on December 21. 

 The cold produced was much greater than before, namely — 68^4- ; this seems 

 to have proceeded partly from the air and materials having been 12° colder in 

 this, than in the former experiment, and partly from the snow having been added 

 faster, so that the mixture arrived at its greatest degree of cold in 20"^, vi^hereas 

 it before took up 46"™. Another reason is, that the former mixture was made 

 in too small ajar, in consequence of which it was poured into a larger before the 

 experiment was completed, by which some cold was lost. The quantity of snow 

 used in this experiment was less than in the former, so that the strength of the 

 acid after the experiment was about .343. The mixture also grew much thicker, 

 and had a degree of elasticity resembling jelly. 



Great as the foregoing degree of cold is, Mr. M'Nab, on Feb. 2, produced 

 one much greater. In hopes of obtaining a greater degree of cold by previously 

 cooling the materials, he cooled about 7 ounces of oil of vitriol, whose strength 

 was .629, that is, rather stronger than the foregoing, by placing the jar in 

 which it was contained in a freezing mixture of oil of vitriol and snow ; the 

 snow intended to be used was also cooled by placing it under the vessel in which 

 the freezing mixture was made. As soon as the acid in the jar was cooled to the 

 temperature of — 57°4-, a little of the snow was added, on which it immediately 

 began to freeze, and rose to — 36° ; but in about 40 minutes, as the jar was 

 still kept in the freezing mixture, it sunk to — 48° ; by which time it was 

 grown very thick and gritty, especially at bottom. More of the cooled snow 

 was then added, which in a short time made it sink to — 78°-i-, and at the same 

 time the thickness and tenacity of the mixture diminished ; so that by the time 

 it arrived at the greatest degree of cold, very little thickness remained. The 



