Mr. Cavendish’s Account , &c. 
167 
Strength. 
Freezing point. 
0 
>54 
-3 1 * 1 
,411 
— if l f 
.38 
-45* J 
.243 
~44i )a 
,21 
-17 J 
As fome of thefe properties, however, were deduced from 
reafoning not fufficiently eafy to flrike the generality of readers 
with much conviction, Mr. M c Nab was defired to try fome 
more experiments to afcertain the truth of it ; which he was fo 
good as to undertake, and has executed them with the fame 
care and accuracy as the former. 
For this purpofe, I fent him fome bottles of fpirit of nitre 
of different ftrengths, and he was defired to expofe each of 
thefe liquors to the cold till they froze ; then to try their tem- 
perature by a thermometer; afterwards to keep them in a 
warm room till the ice was almofl melted, and then again ex- 
pofe them to the cold, and, when a confiderable part of the acid 
had frozen, to try the temperature a fecond time ; then to 
decant the unfrozen part into another bottle, and fend both 
parts back to England, that their ftrength might be examined. 
The intent of this fecond expofure to the cold was as fol- 
lows. Spirit of nitre bears, like other liquors, to be cooled 
greatly below its freezing point without freezing : then the 
congelation begins fuddenly ; the liquor is filled with fine 
fpicula of frozen matter, and the ice becomes fo loofe and 
porous, that, if the procefs be continued long enough for a 
confiderable portion of the acid to congeal, fcarce any of the 
fluid part can be decanted : whereas, if it be heated in this 
flate till the frozen part is almofl, but not intirely* melted, 
and 
