Congelation of ^ui elf her in England. 201 
perceived the mercury had already acquired the confiftence of 
an amalgam, and after immerfing it again for a few minutes, 
and then taking out and inverting it, I was gratified for the firft 
time with the fight of mercury in a ftate of perfect congela- 
tion. I applied my hand to the inverted glafs bulb ; this foon 
loofened the folid mercury, which, on fhaking the hydro- 
meter, was diftinCtly heard to knock with force againft the 
glafs; it was then immerfed a fecond time, and whefi taken 
out was found adhering to the glafs as before. I now inverted 
the glafs again, and kept it in that fituation until the whole of 
the mercury melted, and dropped down globule after globule 
into the ftem of the hydrometer. The interval of time from 
taking the mercury out of the frigorific mixture in a folid ftate, 
the laft time, to its perfect liquefaction, was not noticed ; but, 
upon recollection immediately afterwards, was fuppofed to be 
not lefs than three or four minutes. In a fucceeding experi- 
ment this circumftance was attended to, and the frozen mer- 
cury, weighing feven fcruples, was not entirely melted under 
feven minutes, the temperature of the air +30°. 
The experiment which follows I confider the moft extra- 
ordinary, becaufe it proves beyond a doubt, that mercury may 
be frozen not only here in fummer, but even in the hotteft 
climate, at any feafon of the year, by a combination of fri- 
gorific mixtures, in the way deferibed in the Philofophical 
TranfaCtions, Vol. LXXVIL p. 285. in w r hich attempt to 
freeze mercury, made April 20, 17 87, the temperature of 
the air and materials being + 45°, I certainly reached (without 
the affiftance of fnow or ice) the point of mercurial congela- 
tion ; but had then no fatisfaftory proof that any part of the 
mercury was abfolutely congealed. 
Exp* 
