Experiments on the freezing of Acids. 171 
degree more, the phial was taken out and agitated. This 
mixed the icy filaments with the acid, and made it freeze, which 
it feems not to have done before, in confequence of which its 
temperature rofe to ~4i°f. After having melted the greateft 
part of thefe filaments, and again expofed it to the freezing 
mixture, fome fnow accidentally fell into the acid, and made 
an uncertainty in the freezing point, for which reafon it is not 
let down. But as it is evident, that the quantity of congealed 
matter in the firffc experiment was excefiively fmall, the 
ftrength of the unfrozen part could not differ fenfibly from 
that of the whole mafs, and therefore -41°! is the true 
freezing point that anfwers to the ffrength of ,561. 
It is remarkable, that N° 8. acquired by congelation a 
bluifh colour, not unlike that which the dephlogifticated ni- 
trous acid, in Mr. M c Nab’s former experiments, acquired by 
dilution with fnow. It is not faid, how long the acid re- 
tained this colour, but it was intirely gone when the phial 
arrived in England. I am quite at a lofs to account for this 
phenomenon, and why it happened to this bottle only. 
N° 1 2. when cooled to - 1 f feemed to contain many icy 
particles; but as it afterwards bore to be cooled to -48°, 
without their increafing, we may conclude, that they were 
not frozen fpirit of nitre, but only fome heterogeneous matter 
feparated from it. A little of the congealed part of N° 8. 
dropped into it while at this point, made it freeze, and it rofe 
to - 39 0 . 
In all the foregoing acids the ice was heavier than the fluid 
part, and in confequence fubfided to the bottom ; a proof 
that it was the fpirituous congelation which had taken, place 
in them: but in N J 13. the frozen part fwam at top, which 
fhews, that the congelation was of the aqueous kind. 
It 
