268 Mr. Keir’s Experiments on 
which does not fmoke), were found, by his trials, to be fuf* 
ceptible of this fpecies of congelation. The acid, thus con- 
gealed, has been called glacial, or icy oil of vitriol. 
The other kind of congelation has been little noticed till 
lately. To this congelation every kind of vitriolic acid is fub- 
jedt, whether it fmokes or- not, and whether it has been pre- 
pared from martial vitriol, or from fulphur, provided the 
cold to which it is expofed be lufficiently intenfe : for the 
cold, requinte for this fpecies of congelation, is confiderably 
greater than what is fufficient for the former. 
Mr. Macq^jer relates, in the fecond edition of his 'Dictionary 
of Chemiftry *, that the Duke d’Ayen had obferved the conge- 
lation of concentrated vitriolic acid, which had been expofed to a 
cold expreffed by 13 or 14 degrees below o of Reaumur’s 
fcale ; but that mixtures, con lifting of one part of the above- 
mentioned concentrated acid, with two or more parts of water, 
could not be frozen by the cold to which he expofed them, till 
Te had diluted the acid fo much, that its denfity was to that 
^f water as Jp4'j to 96; in which latter cafe of congelation, 
^it is probable, that the water only did freeze, as it does in 
dilute Solutions of neutral falts. M. de Morveau -f- has made 
Timilar experiments, with a view to verify thofe of the Duke 
d’Ayen, and with limilar fuccefs. By means of an intenfe 
cold, produced by adding fpirit of nitre to pounded ice, he 
•congealed a part of fome vitriolic acid, which he had pre- , 
vioully concentrated. He obferved, that although a very in- 
tenfe cold had been employed to freeze the concentrated acid, it 
neverthekfs remained congealed in much lefs degrees of cold, 
and that it thawed very flowly. Laftly, lome experiments 
* Article, Vitriolic Acid. 
f Mem. de I’Acad. dc Dijon, pour 1782. 
have 
