278 Mr. Keir’s Experiments on 
felves ; or, in other words, that the cold generated by the 
liquefa&ion of ice and of congealed acid are in the above 
proportion of the times, from the following consideration ; 
that, as during the liquefaction of the ice, its temperature 
remains Stationary at 32 0 , and during the liquefaction of the 
acid, its temperature remains about 44 0 or 45 0 , the ice, being 
considerably colder than the acid, will take the heat from the 
contiguous air much fatter. 
The experiment does however (hew, that a confiderable 
quantity of cold is generated by the liquefaction of this acid ; 
and hence it appears probable, that in making experiments of 
producing cold artificially, by mixing fnow with acids in very 
cold temperatures, it would probably be ufeful to employ a 
vitriolic acid of the proper denfity for congelation, and to 
freeze it previoufly to its mixture with fnow. 
It muff: not, however, be imagined, that the cold generated 
by the mixture of thefe two frozen fubftances is nearly equal 
to the fums of the colds generated by the feparate liquefactions 
of the congealed acid and ice, when Singly expofed to a thaw- 
ing temperature : for the mixture refulting from the lique- 
faction, confuting of the vitriolic acid and the water of the 
fnow, appears, from the generation of heat which occurs in the 
mixture of thefe ingredients in a fluid Slate, to be fubject: to 
different laws relatively to heat, than either of the ingredients 
feparately. And the heat, thus generated, as foon as the 
congealed acid and ice are brought to a fluid ffate, muff coun- 
teract:, in fome meafure, the cold produced by the lique- 
faction. 
The vitriolic acid, like water and other fluids, is capable of 
retaining its fluidity when cooled confiderably below its freez- 
ing point. I placed a phial, containing fome congelable 
vitriolic 
