Experiments on freezing Mixtures . 267 
by the melting of the fnow and by that of the acid ; whereas, if 
the acid had been in a fluid ftate, cold would have been pro- 
duced only by the firft caufe, and confequently a greater de- 
gree of cold fhould be produced in this experiment than in the 
former. The only inconvenience attending the acid being 
in a ftate of congelation is, that in all probability it does not 
unite to the fnow fo readily as when in a fluid ftate ; but the 
difference feems not material, as the cold was produced, and 
the materials melted, in 5 minutes. 
27. The day before, Mr. M c Nab, by adding fnow to fome 
of the fame acid in the ufual manner, when the cold of the- 
materials was —46°, produced a cold of only -66°. 
28. In thefe four laft experiments the acid was reduced, by 
the addition of the fnow, to the ftrengths of >325, ,343, >403* 
and ,334 ; and the cold produced in them was before faid to 
be — 55°f 5 — 68°J, —7 8°|, and -66°; whence we may con- 
elude, that thefe are nearly the points of aqueous congelation 
anfwering to the foregoing ftrengths ; only it appears, from 
what was faid in Art. 24. that the ftrengths here fet down are 
all of them rather too fmall. 
Though it is certain that oil of vitriol is capable of the fpi« 
rituous congelation, and though it appears, both from the fore- 
going experiments and from fome made by the Due d’Ayen * 
and by M. de Morveau t> that it freezes with a lefs degree of 
cold when ftrong than when much diluted, it is not certain 
whether it has any point of eafieft freezing, like fpirit of nitre, 
or whether the cold required to freeze it does not continually 
diminifh as the ftrength increafes, without limitation ; but the 
latter opinion is the molt probable. For the Due d’A yen’s and 
* Diction, de Chym. par Macquer, 2 dc edit. 
f Nouv. Mem. de l’Academ. de Dijon, 1782, i er femeflre, p. 68. 
Mm2 
M. 
