386 Intelligence and Miscellaneous Articles. 



containing each 600 grains of water, having been exposed to evapo- 

 ration during seven days, the temperature of the surrounding atmo- 

 sphere varying from 20° to 25°, it was found, that at the end of that 

 time the porcelain vessel had lost 303 grains of its previous weight, 

 the metallic one 277, and the glass vessel 275*5 grains only. The 

 author enters into considerable detail as to the precautions he took 

 to make sure that these differences could not be attributed to any 

 difference in the radiating or conducting powers of the vessels em- 

 ployed. 



The differences observed in the temperature of liquids according 

 to the nature of the vessels in which they are contained, depends, no 

 doubt, on the property with which these vessels appear to be en- 

 dowed, of accelerating or delaying evaporation. It is evident that 

 in each case the quantity of sensible heat subtracted from the liquid, 

 or, in other words, the diminution of its temperature, must be in 

 proportion to the quantity of vapour formed. For instance, the fact 

 that water and alcohol are constantly colder in a porcelain vessel 

 than in a similar vessel of metal or glass, is the natural result of the 

 more rapid evaporation of these liquids from the former of these 

 vessels than from the two latter. The reason why a porcelain vessel 

 evaporates more freely than a metallic or glass one is far less evi- 

 dent. The author has proved, by placing a hermetically-closed bottle 

 of porcelain containing water under the vacuum of the uir-pump, 

 that it cannot be owing to any perviousness of the sides of the vessel, 

 as he was at first inclined to suspect. 



3. The influence of the mass or depth of a liquid was next exa- 

 mined. The author's experiments appear to lead to the curious fact, 

 that the rapidity with which any given liquid evaporates depends 

 not only on the extent of its surface, but also, within certain limits, 

 on its depth. He found, for instance, that with two similar cylin- 

 drical porcelain vessels, containing, the first a layer of water of one- 

 twelfth of an inch in depth, and the second a layer of half an inch, 

 the evaporation from the latter exceeded that of the former in the 

 proportion of nearly 4 to 3. A similar result was obtained with 

 alcohol. If thin glass vessels were used, the same increase of depth 

 accelerated the evaporation in the proportion of 6 to 5. As the 

 author himself observes, this apparent influence of the depth of a 

 liquid on its evaporation, may very possibly be merely owing to the 

 greater facility with which the different layers are conveyed one 

 after the other to the surface, when the liquid is of a certain depth 

 than when it is quite shallow. 



4. Water containing a solution of salt in about the same propor- 

 tion as sea- water, evaporates less rapidly, and consequently produces 

 less cold than the same quantity of distilled water. The higher the 

 temperature of the surrounding atmosphere, the greater the differ- 

 ence between the quantities of salt and fresh water evaporated in a 

 given time under similar circumstances. 



5. A given quantity of water, mixed with certain pulverulent 

 substances, such as siliceous sand, for the particles of which it has 

 but a slight adhesion, evaporates more rapidly than the same quan- 



