VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 581 



Exper. 2. On December 30, 3 oz. of a mixture composed of strong fuming 

 nitrous acid 2 parts, and strong vitriolic acid and water each 1 part, were cooled 

 in a half-pint tumbler immersed in a frigorific mixture, till the temperature of 

 the diluted mixture of acids was reduced to — 30°. The tumbler was then re> 

 moved out of the mixture, and vitriolated natron (Glauber's salt) in very fine 

 powder, previously cooled to — 14" by a frigorific mixture, added by degrees to 

 the liquor in the tumbler, stirring it together till the mercury in the thermo- 

 meter sunk to — 54°. The hydrometer used in the former experiment, with its 

 lower bulb ^ full of mercury, was now immersed and stirred about in the mix- 

 ture for a few minutes, when on taking it out, and inverting it, he had the satis- 

 faction to find the same proof of the mercury being frozen as in the former in- 

 stance. Nearly 4 oz. of the powdered salt was added ; but some was added after 

 the greatest effect was produced. The temperature of the room in which these 

 experiments were made was -j- 30° each time, and the mercury taken from a jar 

 containing several pounds. 



Exper. 3. By an experiment made purposely on January 10, 1789, Mr. W. 

 found that mercury may be congealed tolerably hard, by adding fresh fallen 

 snow, at the temperature of -j- 32°, to strong fuming nitrous acid, previously 

 cooled to between — 25° and — 30°, which may be very easily and quickly 

 effected by immersing the vessel containing the acid in a mixture of snow and 

 nitrous acid. He used the fuming nitrous acid on all occasions, because that 

 does not require to be diluted, cold being immediately produced on the smallest 

 addition of snow. 



Exper. A. On January 12, at Dr. Thomson's request, Mr. W. repeated the 

 experiment of freezing mercury, at the Anatomy School in Christ Church, in 

 the presence of the Honourable Mr. Wenman, the Rev. Dr. Hoare, Dr. Sib- 

 thorp, junior, Dr. Thompson, the Rev. Mr. Jackson, of Christ Church, and 

 Mr. Wood of this place, a gentleman well known for his ingenuity in me- 

 chanics. For this purpose were provided a spirit thermometer graduated very 

 low, and a mercurial thermometer graduated to — 7^°, two thermometer-glasses, 

 with bulbs very near, if not quite an inch in diameter each, one filled with mer- 

 cury nearly to the orifice of the tube, which was left open, the other with its 

 bulb half filled, and an hydrometer with its lower bulb, considerably less than 

 either of the others, likewise half filled with mercury ; the temperature of the 

 room at this time -^ 28°. 



A pan, containing Q oz. of the mixture of acids prepared as in the first ex- 

 periment, was placed in a larger pan, containing nitrous acid, and this, in a 

 frigorific mixture of nitrous acid and snow, contained in another pan much 

 iarger. When the nitrous acid in the 2d pan was cooled by this mixture to 

 — 1 8°, and the mixed acids in the smallest pan nearly as much, snow at some- 



