XIX. Experiments on the Congelation of ^uickfher in England. 
By Mr. Richard Walker ; in a Letter to Henry Cavendifh, 
Ejq, F. R. S. 
Read May 28, 1789. 
s 1 R, 
T NOW beg leave to trouble you with the particulars of my 
experiments relative to the congelation of mercury ; to 
which I fhall add an account of a few experiments, relating to 
the produdtion of artificial cold, made fince my laft Paper was 
written. 
Exp. 1. On December 28th laft, a favourable opportunity 
offered of beginning fome experiments on the congelation of 
mercury, which I was defirous of effecting completely ; how 
far I have fucceeded will appear in the fequel. 
For this purpofe I prepared a mixture of diluted vitriolic acid 
(reduced by water till its fpecific gravity was to that of water 
as 1,5596 to 1) and ftrong fuming nitrous acid, of each equal 
parts. I preferred this mixture of acid becaufe it has been 
found by Mr. M c Nab, in Hudfon’s Bay, to be capable of 
producing much greater cold, when the temperature of the ma- 
terials at mixing is very low, than the nitrous acid alone; the 
former finking a fpirit thermometer to —54°!, the latter never 
lower than — 46°. 
The glafs tube of a mercurial thermometer, with its bulb 
half filled with mercury, was provided, this occurring tome 
H h 2 as 
