no 



HEAT OR CALORIC. 



" A thin dish, or pane oi 

 glass, covered by a small 

 quantity of water, and situ- 

 ated over some concentra- 

 ted sulphuric acid, in a 

 broad vessel, is placed on 

 the air pump plate within a 

 receiver, as represented in 

 this engraving. Under these 

 circumstances, the exhaus- 

 tion of the receiver causes 

 the congelation of the wa- 

 ter." 



12. Wollaston's Cryophorus. 



" The adjoining figure represents the Cryophorus, or 

 frost bearer ; an instrument, invented by the celebrated 

 Wollaston, in which congelation is produced in one cav- 

 ity, by the rapid condensation of vapor in another." 



" In form, this instrument obviously differs but little 

 from the palm glass, already described (46.) It is sup- 

 plied by the same process, with a small portion of water, 

 instead of alcohol ; so that there is nothing included in it, 

 unless water, either liquid, or in vapor." 

 , , " The Cryophorus being thus made, if all the water be 

 r j allowed to run into the bulb near the bent part of the tube, 

 ^ "* and the other bulb be immersed in a freezing mixture, 

 the water will freeze in a few minutes." 



" So long as no condensation is effected, of the thin aqueous vapor, 

 which occupies the cavity of the instrument, that vapor prevents, by 

 its repulsion, the production of more vapor : but when, by means of 

 cold, the vapor is condensed in one bulb, its evolution in the other, 

 containing the water, being unimpeded, proceeds rapidly. Mean- 

 while the water becomes colder, and finally freezes, from losing the 

 caloric which the vaporization requires." 



" According to Wollaston, one grain of water, converted into va- 

 por, holds as much caloric as would, by its abstraction, reduce thirty 

 one grains from 60 Fahr. to the freezing point ; and the caloric re- 

 quisite to vaporize four grains more, if abstracted from the residual 

 twenty seven grains, would convert them into ice. 



