PROPERTIES OP DIFFERENT EARTHS. 37 



15° in half an hour, and the chalky earth lost by the same 

 exposure 4°. 



Equal quantities of fertile brown soil, and of sterile 

 clay, were dried ; and their temperature raised to 88° ; upon 

 being then exposed to air at the temperature of 57°, the 

 brown soil lost, in the space of half an hour, 9°, and the 

 clay 6° ; moistened clay at 88°, exposed to a temperature 

 of 55°, fell to the same in less than a quarter of an hour.* 



The variations of temperature in soils of different na- 

 tures, with their several degrees of affinity for heat, and of 

 power for retaining it, deserve the attention of the agri- 

 culturist. The only instrument necessary for conducting 

 experiments upon this subject, is a good thermometer ; and 

 by the aid of that we can ascertain the kind of soil suited 

 to any one species of plant, since all do not require the 

 same intensity, nor the same continuance of heat. 



The different degrees of heat which earths imbibe at 

 the same temperature is known to most agriculturists, and 

 many of them turn the knowledge to advantage. It is 

 customary with those who cultivate the table lands upon 

 the sides of the Alps, to throw black earth upon the snow, 

 in order to hasten its thawing, that they may commence 

 their cultivation as soon as the sun returns to them. The 

 same means are employed in green-houses and orangeries ; 

 the walls are blackened, and the soot spread over the soil 

 serves to concentrate and fix the heat, to such a degree, 

 that in the month of July, upon the Cramont, at an eleva- 

 tion of 9077 feet, where the temperature was at 43°, M. 

 Saussure found that a thermometer which was placed in a 

 box lined with blackened cork, and of which the opening 

 was closed by three glasses placed at some distance from 

 each other, rose in two hours from 38° 75' to 99° 5(y. 



Independently of the heat which the atmosphere com- 

 municates to the soil, and of the modifications wrought 

 upon it by the color of the constituent principles, it is in 

 the power of art to lessen or to increase the temperature of 

 lands at will. Animal manures develope more or less 

 heat, according to their nature, and their state of fermen- 

 tation ; those which have not been decomposed, excite 

 more heat, and maintain it for a longer time, than others. 



[* See Davy, p. 179, 180. Chaptal has reduced his degrees erro- 

 neously, and they are corrected as above &om Davy's Jgrictdtiwal 

 Chemistry.— Tr.] 

 4 



