584 PHILOSOPHICAL TRANSACTIONS. [aNNO l/SQ. 



tube. On reflecting on this circumstance afterwards, it occurred to Mr. W. 

 that the further descent of the mercury in these experiments was prevented not 

 solely by the mercury freezing in the tube, the cause commonly assigned, but 

 rather by the quick formation of a spherical shell of solid mercury within the 

 bulb, by the sudden generation of cold. 



Dr. Beddoes expressing a desire to exhibit solid mercury at his lecture before 

 bis class, Mr. W. undertook to freeze some at the Laboratory on March 1 2th, 

 and now resolved to satisfy himself respecting the cause which prevented the 

 lower descent of the mercury in his former experiments. In this, as well as the 

 former, the mercury in a thermometer graduated to — 6o°, and likewise in a 

 thermometer-glass, filled nearly to the orifice, which lengthened its scale to 

 near — 250°, sunk only a few degrees below the point of mercurial congelation, 

 and then remained stationary. After waiting some time, he took the thermo- 

 meter out of the mixture, and observed the bulb apparently full, and the short 

 thread of mercury above unbroken. He now embraced the lower part of the 

 tube with his hand a few seconds, resting it on the upper part^of the bulb ; and 

 on taking it away, he found that the whole of the mercury had subsided into 

 the bulb, which it did not now quite fill, a small space at the top of the bulb 

 remaining empty. He then took out the thermometer glass, and applied his 

 hand to the tube ; but the mercury remained stationary till he sunk his hand so 

 as to communicate heat to that part of the bulb which is immediately connected 

 with the tube, when the thread of mercury dropped entirely into the bulb. It 

 was now immersed again for a short time, then taken out, and the shell of glass 

 beaten off, which exposed a globe of solid mercury, nearly an inch in diameter. 

 This bore several very smart strokes with a hammer before it began to liquefy, 

 but was not perfectly malleable. In the course of these experiments, several 

 fragments of the solid mercury were thrown into mercury in its ordinary liquid 

 state, and were found to sink with considerable celerity. 



In continuing his researches respecting the means of producing artificial cold, 

 Mr. W. found that phosphorated natron produces rather more cold by solution 

 in the diluted nitrous acid than the vitriolated natron. At the temperature of 

 + 50°, 4 parts of the diluted nitrous acid, prepared by mixing strong nitrous 

 acid with half its weight of water, required 8 parts of that neutral salt in fine 

 powder to be added, in order to cause the thermometer to sink to — 6° ; and 

 again, by the addition of 5 parts of nitrated ammonia in fine powder, the ther- 

 mometer sunk so low as — l6°, in the whole 66°. A mixture of this kind made 

 the thermometer sink from 80°, the temperature of the materials before mix- 

 ing, toO^ 



Mr. W. was directed to the trial of this salt, by the like remarkable sensation 

 of coldness without pungency, which, with its other similar properties to ice. 



