the Point of Congelation . 28 y 
“ was replaced, when Ice foon began to form at the bottom, 
“ like feathered cryftals, which however (hot out very flowly. 
“ But upon ftirring the folution, a vaft number of ftellated 
“ feathered cryftals prefently formed in it, the thermometer 
“ rofe immediately to 7°!, and was foon got to 8 C .” I have 
tranfcribed thefe remarks, not only becaufe they elucidate 
fome of the phaenomena mentioned in former experiments, but 
likewife on account of the ftriking analogy the cryftals bore to 
the configurations obferved in a drop of the folution of this 
fait viewed with the microfcope. As the drop dries, great 
numbers of feathered cryftals Ihoot out from its edges, and 
fome more perfect ftellated cryftals are often formed in the 
middle; of which a pretty exadl reprefentation may be feen in 
Baker’s Employment for the Microfcope (p. no. PL II.). 
The refemblance of both kinds of cryftals, in thefe two dif- 
ferent fituations, is very great; and their particular figure is 
probably due to the fame caufe, a confufed and conftrained 
cryftallization, occaftoned in the one cafe by the hafty evapo- 
ration and want of room in the drop, and in the other cafe by 
the watery congelation afting upon and embarrafting the natu- 
ral tendency of the fait. 
A ftronger folution of fal ammoniac, the proportions being 
1 : 4, exhibited a ftitl more beautiful appearance ; for, be- 
fide the feathered cryftals at bottom, and the ftars floating in 
the middle, a third fort of cryftals, moft refembling the ftars, 
attached themfelves to the ftdes of the tumbler, and were feen 
through the glafs as compofing a great variety of brilliant 
j'acettes. In this experiment the folution was reduced below 1% 
before any congelation began to take place, and a certain quan- 
tity of the fait fell to the bottom in the form of a white pow- 
der, about as much as reduced the liquor to the ftate of a 
faturated 
