582 PHILOSOPHICAL THANSACTIONS. [aNNO 17 6Q. 



what between + 20° and -{- 25°. the temperature of the open air at that time, 

 was added to the nitrous acid in the 2d pan, till the spirit thermometer sunk to 

 near — 43°; then the thermometer, with its bulb half filled, was immersed a 

 sufficient time, and when taken out, the mercury in it was found congealed, 

 and adhering to the glass. The pan containing the mixed acids, and which had 

 been removed while the snow was added to make the 2d mixture, was now re- 

 placed in it, in order to be cooled ; and when the mixture of acids was reduced 

 to the; temperature of — 34°, snow previously cooled to — 1 8° was added, 

 keeping the mixture stirred till the mercurial thermometer sunk to — 60^^ ; its 

 temperature by the spirit thermometer was then found to be — 51°. 



The 3 glasses, containing the mercury to be frozen, were now immersed in 

 this mixture, and having been moved about in it for a considerable time, during 

 which the spirit thermometer rose scarcely 1°, were then severally taken out and 

 examined. When the freezing mixture was supposed to have produced its 

 effect, the bulb which was completely filled was taken out, and broken on a flat 

 stone by a moderate stroke or 2 with an iron hammer. This bulb was 1 1 or 



. 12 lines in diameter. The solid mercury was separated into several sharp and 

 brilliant fragments, some of which bore handling for a short time before they 

 returned to a fluid form. One mass, larger than the rest, consisting of nearly 

 4- of the whole ball, afforded the beautiful appearance of flat plates, converging 

 towards a centre. Each of these plates was about a line in breadth at the ex- 

 ternal surface of the ball, becoming narrower as it shot inwards. These facets 

 lay in very diflerent planes, as is common in the fracture of any crystallized ball, 

 whether of a brittle metal or of the earths, as in balls of calcareous stalactite. 

 The solid brittle mercury in the present instance bore a very exact resemblance, 

 both in colour and plated structure, to sulphurated antimony, and especially to 



, the radiated specimens from Auvergne, before they are at all tarnished. 



Instead of a solid centre to this ball, it seemed as if there had been a central 

 cavity, of about 2 lines in diameter, a considerable portion of which was evi- 

 dent in the fragment just described, at that part to which the radii converged. 

 It is indeed possible, that this may have been merely the receptacle of some part 

 of the mercury remaining fluid at the centre. The hollow within was shining, 

 but its edges were neither soft nor mouldering ; on the contrary, they were 

 sharp and well defined: nor was the brilliancy of the radii attributable to any 

 exudation of mercury as from an amalgam. In the 2 smaller bulbs, which were 

 only half filled, the mercury preserved its usual lustre on the surface in contact 

 with the glass, as well as on that surface which it had acquired in becoming 

 solid. The latter was occupied by a conical depression, the gradations of which 

 were marked by concentric lines. One of these hemispheres was struck v^^ith a 

 hammer, as in the former instance, but was rather flattened and crushed than 



