MERCURY. 
557 
These experiments, made by a person of un- 
doubted veracity, would have been sufficient to set 
aside the notion that fluidity was an essential pro- 
perty of quicksilver, even if that had not been done 
before by Mr. Braun, professor of philosophy at 
Petersburg. This gentleman had recourse to art to 
effect that which Nature had done for Pallas. He 
availed himself of a good opportunity for the pur- 
pose on the 1 4th of December, 1759 , when the 
mercury in the thermometer stood in the open air 
at — 34°, which is now known to be only five or six 
degrees above its point of congelation. Assisting 
this natural cold, therefore, with a mixture composed 
of aqua-fortis and pounded ice, his thermometer was 
sunk to — 69 °. Part of the quicksilver must now have 
been really congealed, but unexpected by him, and 
he only thought of pursuing his object of producing 
still greater degrees of cold ; and having expended 
all his pounded ice, be was obliged to use snow in- 
stead of it. With this fresh mixture the mercury 
sunk to — 100 , — 240, and — 350°. On removing the 
thermometer he found it whole, but the quicksilver 
was fixed, and continued so for twelve minutes. The 
experiment was repeated with another thermometer, 
which was graduated only to 220 degrees below zero, 
when all the mercury sunk into the ball and became 
solid as before. 
Mr. Braun now suspected that the quicksilver 
was really frozen, and prepared for making a de- 
cisive experiment. This was accomplished on the 
twenty-fifth of the same month, and the bulb of the 
