Congelation of ^uickjilver in England. 203 
the veffel containing the acid in a mixture of fnow and nitrous 
acid. 
I ufe the fuming nitrous acid upon all occafions, becaufethat 
does not require to be diluted, cold being immediately pro- 
duced on the fmakeft addition of fnow. 
Exp. 4. On January 12, at Dr. Thomson’s requefr, I 
repeated the experiment of freezing mercury, at the Anatomy 
School in Chrift Church, in the prefence of the honourable 
Mr. Wenman, the rev. Dr. Hoare, Dr. Sibthorp, junior, 
Dr. Thompson, the rev. Mr. Jackson of Chrift Church, 
and Mr. Wood of this place, a gentleman well known for 
his ingenuity in mechanics. 
For this purpofe were provided a fpirit thermometer gra- 
duated very low, and a mercurial thermometer graduated to? 
— 76°, two thermometer glades, with bulbs very near, if not 
quite, an inch in diameter each, one filled with mercury 
nearly to the orifice of the tube, which was left open, the 
other with its bulb half filled, and an hydrometer with its 
lower bulb (confiderably lefs than either of the others) like- 
wife half filled with mercury ; the temperature of the room at 
this time -f 28°. 
A pan, containing nine ounces of the mixture of acids pre- 
pared as in the firft experiment, was placed in a larger pan, 
containing nitrous acid, and this, in a frigorific mixture of 
nitrous acid and fnow, contained in another pan much larger. 
When the nitrous acid in the fecond pan was cooled by this 
mixture to — 18 0 , and the mixed acids in the fmalleft pan 
nearly as much, fnow at fomewhat between -j-20° and +25% 
the temperature of the open air at that time, was added to the 
nitrous acid in the fecond pan, until the fpirit thermometer 
funk to near — 43 0 ; then the thermometer, with its bulb 
half filled, was immerfed a fufficient time, and when taken 
