106 HEAT OR CALORIC* 



was 50 higher than that of boiling water," viz. at 262 Fahr. *' The 

 temperature of their bodies was not at all raised, though their watch 

 chains and every thing else metallic about their persons were so heat- 

 ed, that they could not bear to touch them.* The thermometers 

 which hung in the rooms always sunk several degrees when either of 

 the experimentalists touched them, or breathed upon them. Some 

 eggs and a beefsteak were placed on a tin frame ; the eggs were 

 roasted hard in twenty minutes, and the beefsteak was overdone in 

 thirty three minutes. Water placed in the same room did not how- 

 ever acquire a boiling heat until a small quantity of oil was dropped 

 on it, when it soon began to boil briskly. The evaporation from the 

 surface of the water had prevented it from acquiring the heat of 212 ; 

 but when that surface became covered with a film of oil, the evapora- 

 could not go on, and ebullition commenced. "f 



" The oven girls in Germany often sustain a heat of from 250 to 

 280, and one of these girls once breathed for five minutes, in air 

 heated to 325 of Fahr. When the air of such rooms is damp, or the 

 skin is rubbed over with varnish, the heat cannot be borne an instant. " J 



In the case of Sir Joseph Banks and Sir Charles Blagden, it is 

 stated that there was no remarkable evaporation from the skin ; the 

 insensible perspiration was doubtless greatly increased, and in such 

 cases an immense perspiration usually happens, and it is this chiefly 

 which either in a sensible or insensible form, renders such trials safe. 

 , A well varnished man would probably soon die in such circumstan- 

 ces, and probably could not live long at the common temperature.^ 



The cooling of liquors in hot countries, is effected by evaporation 

 from skins containing water, from porous jars, &c. 



Mr. Leslie, with the aid of sulphuric acid to absorb the vapor, froze 

 water by its own evaporation under the exhausted receiver ; some- 

 times he employed merely porous solids, as clay, or parched oat meal 

 or flour, porous and burnt whin stone,\\ and porous, and ignited pieces 

 of muriate of lime.lT 



If the water has been previously boiled, the ice formed is firmer, 

 although the process is slower. An earthen ware vessel is pre- 



* " The heat of metals at 120, is scarcely supportable ; water scalds at 150, but 

 air may be heated to 240, without being painful to our organs of sensation." Davy. 



t Phil. Trans. Vol. LXXVI, p. 271, Ann. 1775. Quoted by Mr. Parkes. Es- 

 says, 2d Lond. Edit. Vol. I, p. 70. t Parkes, quoting Hist. Acad. Sciences, 1764. 



Communicated. Since reading " Wells on Dew," I have doubted whether the 

 power of the animal system to endure such a high temperature were owing entirely 

 to the cooling effects of evaporation. Physiologists maintain that this power of the 

 animal system to endure a high heat, is connected with the vital principle. V. Sir 

 Everard Home, in Phil. Tran. 



|| The Scotch colloquial name for greenstone and other trap rocks. 



IT The Pacha of Egypt procured a fine air pump for the manufacture of ice by Mr. 

 Leslie's process. 



