[ *77 3 
XVIII. Experiments on the EffeB of various Subfances in lower- 
ing the Point of Congelation in Water . By Charles Blagden, 
M. D. Sec . R. S. and F, A. S. 
Read April 24, 1788. 
T HE experiments which were necefifary, in order to deter*- 
mine what efFedt the admixture of various fublfances 
would produce upon the property of water to be cooled below 
the freezing point*, naturally led me to a more particular confi- 
deration of the power of fuch admixtures in making water 
require a greater degree of cold before it congeals. Many cu- 
rious queftions occurred on this fubjedt, which could only be 
anfwered by frelh experiments. Thefe were made n.early in 
the fame manner as the preceding ; that is, the liquor, whofe 
freezing point I meant to try, was put into a glafs tumbler, 
to the height of two or three inches above the bottom, and 
the tumbler was then immerfed in a frigorific mixture of com- 
mon fait and ice or fiiow. As the objedt was feldom to 
cool the liquor as much as poffible below its freezing point, the 
operation required no particular care, but the frigorific mix- 
ture was commonly permitted to adt with its full force : 
wherefore, fome parts of the liquor were often much colder 
than others ; and particularly, near the top, a thermometer 
would ufually Rand feveral degrees higher than toward the 
bottom, becaufe the furface was conftantly warmed by the air 
of the room. 
* Seep. 125. of this Volume. 
P p 2 
My 
