434 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



stories high, on a small roof facing the west, so that the glass was freely ex- 

 posed to the north-west ; and he mixed with the snow on which it stood 2 drams 

 more of sal ammoniac. The snow and sal ammoniac in the glass soon froze in 

 the open air to a muss like ice : no sensible change however appeared in the 

 quicksilver that evening ; but at 1 in the morning it was found frozen solid. It 

 had divided into 2 large and 4 small pieces ; of the former, one was hemispheri- 

 cal and the other cylindrical, each seemingly rather above a dram in weight; 

 the 4 small bits might amount to half a scruple. The spirit of wine, in an ex- 

 cellent thermometer made by Brander, stood at this time 10° under O of Fah- 

 renheit's scale, which was the cold of Upsal in 1740. Next morning, the 12th, 

 about 7 o'clock, the larger hemisphere began to melt, perhaps because it was 

 most exposed to the air, and not so near as the others to the sal ammoniac mix- 

 ture which lay beneath. In this state it resembled an amalgam, sinking to that 

 side on which the glass was inclined, but without quitting the surface of the 

 glass, to which it was still firmly congealed ; the 5 other pieces had not yet un- 

 dergone any alteration, but remained frozen hard, as in the night. Towards 8 

 o'clock the cylindrical piece began to soften in the same manner as the former, 

 and the other 4 soon followed. About 8 they fell from the surface of the glass, 

 and divided into many fluid shining globules, which were soon lost in the inter- 

 stices of the frozen mixture, and re-united in part at the bottom, being now 

 exactly like common quicksilver. This whole experiment remains involved in 

 such obscurity, that some persons have supposed the quicksilver itself 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 situated in 

 the same latitude as London, and enjoying a temperate climate in general, be- 

 comes subject at times to a great severity of cold. This of the 1 1th of January, 

 1774, is one instance. There are others when the thermometer sunk there to 

 — 12°, — l6°, or — 19 ; and at Cattlenburg, a smalltown about two German 

 miles distant, to — 30°. By watching such extraordinary occasions, experiments 

 on the freezing of quicksilver might easily be performed in many places where 

 the possibility of them is at present little suspected. The cold observed at Glas- 

 gow in 1780 would have been fully sufficient for that purpose, viz. — 23° on the 

 snow, — 14° in the air. 



Dr. Blumenbach's description of the solid quicksilver differs so much from 

 Prof. Braun's, with respect to its colour and general appearance, as to require a 

 particular explanation. Their disagreement, Dr. B. imagines, was occasioned by 

 a diversity in the circumstances of their experiments. Quicksilver crystallizes in 

 becoming solid. In this property it resembles other metallic substances, as ap- 

 pears from many facts, and is elegantly exemplified in those curious cups formed 

 by exposing proper masses of melted metal to the cold air till the outer part be 



