VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 583 



broken. The other, on being divided with a sharp chissel, showed a metallic 

 splendour on its cut surface, but not equalling the polish of a globule of fluid 

 mercury. Thirteen ounces of snow in the whole were found to have been added 

 to the mixed acids ; but some was added to lower its temperature after the 

 glasses containing the mercury were taken out, and the spirit thermometer had 

 risen a few degrees. This was a day remarkably favourable for such an experi- 

 ment. The thermometer exposed to the open air stood, at ^ past 8 this 

 morning, at -j- 6"^, which is a very extraordinary degree of cold here ; biit this 

 experiment v^^as not begun till noon. 



Exp, 5. On Jan. 14, Mr. W. froze mercury at the Anatomy School again, 

 in the presence of the Rev. the Dean of Christ Church, the Rev. Dr. Hornsby, 

 and Dr. Thomson. Four ounces now of the mixture of acids, prepared as in the 

 first experiment, were cooled in a tumbler to — 20°, which required somewhat 

 more than an equal weight of snow, cooled nearly to the same temperature, to 

 produce the greatest effect. This was somewhat less than in the last experiment, 

 the spirit thermometer sinking no lower than — 46°, owing chiefly to the 

 weather having become much warmer, the temperature of the open air being 

 now + 36°. The mercurial thermometer immersed in this mixture sunk to 

 — 55°, where it became stationary ; then 2 thermometer glasses, one half filled 

 with mercury, and the other filled to a considerable height up the tube, after 

 being immersed some time, were examined. On breaking the shell of glass 

 from the former of these, the mercury was found in a perfectly solid state ; but 

 its upper surface, which was highly polished, and of the colour of liquid mer- 

 cury, instead of being only slightly depressed, as had been seen in every other 

 instance which afforded an opportunity for inspection, now formed a perfectly 

 inverted hollow cone. This great depression, as well as the concentric circles 

 mentioned in a former instance, might be owing to a rotatory motion acci- 

 dentally given to it while congealing. The solid mercury was beaten out ; but 

 having been suflTered to lie some time on the table for inspection, very quickly 

 melted into liquid globules. The flexibility of solid mercury was clearly to be 

 observed in this beautiful specimen ; for the external surface, particularly the 

 upper thin rim of the concave part, was evidently bent by the first gentle stroke 

 of the hammer. The globe of mercury in the other glass, which was very 

 small, exhibited nearly the same phenomena, as in the instances before- 

 mentioned. 



It happened in these experiments, contrary to what has generally occurred to 

 others, that the mercury never sunk lower than — 6o°, seldom so low, in the 

 thermometer, and but little below the point of mercurial congelation in the 

 tubes of the thermometer glasses filled nearly up to the orifice, with a view to 

 show the contraction of mercury in becoming solid by its great descent in the 



.\» 



