the Congelation of uickfilyer . 359 
involved in fucli obfcurity, that lome perlons have fuppofed 
the quicklilver itfelf was not frozen, but only covered over with 
ice, to which opinion, however, there are great objections. 
It is worthy of remark, that Gottingen, though fituated in 
the fame latitude as London, and enjoying a temperate climate 
in general, becomes fubject at times to a great l’everity of cold. 
This of the nth of January, 1774, is one inftance. I find 
others when the thermometer funk there to - 12°, — id° or 
*-i 9 0 ; and at Cattlenburg, a fmall town about two German 
miles diftant, to - 30° *. By watching luch extraordinary 
occaflons, experiments on the freezing of quicklilver might 
eafily be performed in many places where the poffibility of 
them is at prefent little fufpedted. The cold obferved at Glal- 
gow in 1780 would have been fully lu ffic ient for that pur- 
pofe y. 
Dr. blumenbach’s defeription of the folid quickfilver dif- 
fers fo much from Profeflor braun’s, with refpect to its colour 
and general appearance, as to require a particular explanation. 
Their difagreement, I imagine, was occasioned by a diverfity 
in the circumftances of their experiments. Quicklilver cryifal- 
lizes in becoming folid. In this property it refembles other 
metallic fubftances, as appears from many fadls, and is ele- 
gantly exemplified in thole curious cups which are formed by 
expoling proper mafles of melted metal to the cold air till the 
outer part be fufficiently hardened to conflitute a folid coat, and 
then letting out the internal fluid part, fo as to leave a hollow iu 
the middle. This concavity is found every where befet with 
metallic cryhals, fcarcely yielding in beauty and regularity to 
* laxmann’s Sibirifche Briefe, p. 98. Nov. Commentar. Petrop. tom. VIL 
P- 39 6 * 
f Viz. — 23° on the fnow, — 14° in the air. Phil. Tranf. vol. LXX. p, 456. 
tlie.- 
