580 PHILOSOPHICAL TRANSACTIONS. [aNNO 178Q. 



It may be proper to premise here, that in all experiments of this kind Mr. 

 W. removes each vessel, when the liquor it contains is sufficiently cooled, out 

 of the mixture in which it is immersed for that purpose, immediately previous to 

 adding the snow or salts with intention to generate a still further increase of 

 cold ; and also prefers adding the snow or powdered salts to the liquor, instead 

 of pouring the liquor on these : it is necessary also to stir about the snow or 

 salts, while cooling in a frigorific mixture, from time to time, otherwise it will 

 freeze into a hard mass, and frustrate the experiment. 



A half-pint glass tumbler, containing 2-|- oz. of the above-mentioned diluted 

 mixture of acids, being immersed in mixtures of nitrous acid and snow, till the 

 liquor it contained was cooled to — 30°, was removed out of the mixture and 

 placed on a table ; snow, likewise previously cooled in a frigorific mixture to 

 — 15°, was added by degrees to the liquor in the tumbler, and the mixture 

 kept stirring till a mercurial thermometer sunk to — 6o^, where it remained sta- 

 tionary ; the hydrometer was then immersed in the mixture (the thermometer 

 glass having been broken in the course of the experiment,) and stirred about in 

 it for a short time, and on taking the hydrometer out, and gently shaking it, 

 the mercury had already acquired the consistence of an amalgam, and after im- 

 mersing it again for a few minutes, and then taking out and inverting it, he 

 was gratified for the first time with the sight of mercury in a state of perfect 

 congelation. Mr. W. applied his hand to the inverted glass bulb ; this soon 

 loosened the solid mercury, which, on shaking the hydrometer, was distinctly 

 heard to knock with force against the glass ; it was then immersed a 2d time, 

 and when taken out was found adhering to the glass as before. He now in 

 verted the glass again, and kept it in that situation till the whole of the mercury 

 melted, and dropped down globule after globule into the stem of the 

 hydrometer. The interval of time from taking the mercury out of the frigorific 

 mixture in a solid state, the last time, to its perfect liquefaction, was not 

 noticed ; but, on recollection immediately afterwards, was supposed to be not 

 less than 3 or 4 minutes. In a succeeding experiment this circumstance was 

 attended to, and the frozen mercury, weighing 7 scruples, was not entirely 

 melted under 7 minutes, the temperature of the air -|- 30°. 



The experiment which follows Mr. W. considers the most extraordinary, be- 

 cause it proves beyond a doubt, that mercury may be frozen not only here in 

 summer, but even in the hottest climate, at any season of the year, by a com- 

 bination of frigorific mixtures, in the way described in the Philos. Trans, vol. 77, 

 p. 285, in which attempt to freeze mercury, made April 20, 1787, the temper- 

 ature of the air and materials being -f 45°, he certainly reached, without the 

 assistance of snow or ice, the point of mercurial congelation ; but had then no 

 satisfactory proof that any part of the mercury was absolutely congealed. 



