286 Dr. Beddoes’s Account of form new Experiments 
appeared to Mr. Walker, below —40", Its thread deemed to 
he divided below that point ; but the froth occalioned by the 
ebullition of the materials prevented* his making fo accurate 
an observation, as he could have wifhed. 
The reafon why this lad mixture reduced the thermometer 
more than the third, though both were of the fame materials, 
and the lad at a lower temperature, Mr. Walker imagines- 
to have been partly becaufe the fourth pan had not another 
immerfed in it to give it heat, and partly becaule the mate*' 
rials were reduced to a finer powder. 
I fhould imagine, that mercury reduced to its freezing point 
will freeze more quickly than water reduced to its freezing- 
point, becaufe it appears, from experiments on their capacity 
for heat, that the latter of thefe bodies has lo much more 
latent heat in its liquid date; which greater quantity of latent 
heat mud, as it becomes fenfible, more retard the congelation.- 
I forbear to enumerate many variations of thefe experiments 
which Mr. Walker has among his notes; but there is one 
mixture which, though its power is not equal to that which I 
have lad defcribed, may prove very l'erviceable in experiments 
of this nature, on account of its cheapnefs. It confids of oil of 
vitriol diluted with an equal weight of water : added to Glau- 
ber’s fait, it produces about 46 degrees of cold.. The addition 
of fal ammoniac renders it more intenfe by a few degrees. One 
remarkable circumdance occurred to Mr. Walker, as he was 
endeavouring to afcertain the bed drength of the vitriolic acid : 
he happened to be trying a mixture of two parts of oil of 
vitriol and one of water, when he obferved, that, at the tem- 
perature of 35 0 , the mixture coagulated as if frozen, and the 
thermometer became dationary ; but, on adding more Glau- 
ber’s fait, it fell again, after fome little time, but fo great a 
5 cold 
