172 Mr, Cavendish’s Account of 
It may appear remarkable to thofe who read Mr. M c Nab’s 
experiments, that thefe acids bore to be heated fo much above 
their freezing points before the ice intirely diffolved. N° 6. 
bore to be heated 18 degrees, N° 7. 13 degrees, and N° 12. 
17 degrees above their freezing points, before all the congealed 
acid had difappeared. But as, ill order to diffolve this con- 
gealed matter, they were brought into a room in all proba- 
bility a great many degrees warmer than the points to which 
they were heated, fo that the liquors heated fall; and as during 
the difiolution the ice would fublide to the bottom ; it is not 
extraordinary, that the fluid part in the phial might be many 
degrees warmer than the frozen part, unlefs the phials were 
much agitated during the time, which nothing fhews them to 
have been ; efpecially if we confider the great quantity of 
heat which, in all probability, muft be communicated to the 
frozen acid in order to melt it ; and that, perhaps, the frozen 
acid may receive and part with its heat but flowly. It mud: 
be obferved, that in N° 6. and 12. the frozen part might very 
likely be of a conflderably different ftrength, and in confe- 
quence its freezing point might be feveral degrees different 
from that of the whole mafs, fo that the temperature to 
which the fluid was heated, in order to melt the ice, might 
very likely not differ fo much from the freezing point of the 
ice itfelf as is here fet down. But this could not be the cafe 
with N° 7. 
It muft be obferved, that when Mr. M c Nab wanted to try 
the temperature of N° 7. after it had frozen in the firft man- 
ner, the ftopper ftuck fo tight that he was not able to remove 
it without warming it before the fire. The thermometer was 
then introduced, and flood feveral minutes therein at+ i°f, or 
4- 2 0 . As the thermometer remained fo long at this point, one 
4 might 
