On a new Mode of Artificial Congelation. 4 1 3 



nnd vvris almost immediately rewarded by the disclosure of a prd- 

 pertv, the application of which blazed on his fancy. n the 

 hionthof Jmie 1810, having introduced a surface of sulphuric 

 acid utider the receiver of an air-pump, he perceived with plea- 

 sure that this substance only superadded Us ,,eculmr attraction 

 for moisture, to the ordinary effects resulting from the progress 

 of exhaustion ; and, what was still more important that it con- 

 tinued to support, with undiminished energy, the dryness thus 

 created. The attenuated air was not suffered, as before, to grow 

 charged with humidity; but each portion of that medium, as fast 

 as it became saturated by touching the wet ball of the hygrome- 

 ter, transported its vapour to the acid, and was thence sent back 

 denuded of the load, and fitted again to renew its attack witli 

 fresh vigour. By this perpetual circulation, therefore, between 

 the exhaling and the absorbing surface, the diffuse residuum of 

 air is mainfained constantly at the same state of dryness The 

 sentient ball of the hygrometer, which had been covered with 

 several folds of wetted tissue paper, was observed, at an early 

 staee of the operation, suddenly to lose its blue tint and assume 

 a dull white, while the coloured liquor sprung upwards in the 

 stem, where it continued, for the space of a minute, stationary, 

 and again slowly subsided. The act of congelation had there- 

 fore, at this moment taken place, and the paper remained frozen 

 several minutes, till its congealed moisture was entirely dispersed. 

 Pursuing this decisive intimation, the hygrometer was removed, 

 and a watch-glass filled with water substituted in its place. By 

 a few strokes of the pump, the whole was converted into a solid 

 cake of ice, which, being left in the rare medium, continued to 

 evaporate, and, after the interval of perhaps an hour, tota ly dis- 

 appeared. A small cup for holding the water was next adopted, 

 and the whole apparatus gradually enlarged. 



Efficient Power nearly the same at all Ttinperatures. 

 The'powers, both of vaporization and of absorption, being 

 ereatly augmented in the higher temperatures, the same lin^it of 

 cold nearly is in all cases attained, by a certain measure of ex- 

 haustion ' When the air has been rarefied 250 times, the utmost 

 that, under such circumstances, can perhaps be effected, the sur- 

 face of evaporation is cooled down 1 20 degrees of Fahrenheit 

 in winter, and would probably sink near 200 in summer. Nay, 

 a far less tenuity of the medium, when combined with the action 

 of sulphuric acid, is capable of producing and supporting a very 

 intense cold. If the air be rarefied only 50 times a depression 

 of temperature will be produced, amounting to 80 or even lUU 

 decrees of F.direnheit's scale. 



