48 CHYMISTRY APPLIED TO AGRICULTURE. 



down; after having poured off the liquor, the residuum 

 must be washed and dried; when its weight will give 

 the quantity of carbonate of lime contained in the earthy 

 mixture. 



If the carbonate of lime, and the other deposits ob- 

 tained, be of a brown color, it is to be presumed, that 

 they contain a mixture of animal or vegetable substance, of 

 which the quality and proportions may be ascertained by 

 throwing them upon a red-hot iron, and holding them over a 

 fire of such a temperature, as will heat the iron to white- 

 ness ; if the smoke arising from them have the odor of 

 burning leather, hair, or feathers, the substance contained 

 in them is animal ; but if it have the smell of wood smoke, 

 it is vegetable. The two substances are sometimes com- 

 bined, but the means of ascertaining in what proportions 

 are beyond the skill of an agriculturist ; I have therefbre 

 thought that I ought to confine myself to the experi- 

 ment necessary for ascertaining their presence. 



The method I have just described is easy, and in the 

 power of any agriculturist, however little informed ; it 

 is not exact, but it furnishes results approximating near 

 enough to the truth, to enable any one to ascertain the 

 nature and proportions of the earthy substances which 

 enter into the composition of a soil. A greater degree 

 of precision in the analysis would require the employ- 

 ment of many agents unknown to the agriculturist, and 

 a habit of analysis which he cannot be supposed to pos- 

 sess. 



But as the salts play an important part in vegetation, 

 and as all soils are in some degree impregnated with 

 them, I believe I ought not to dispense with pointing out 

 the means of recognising them, and for this purpose I 

 shall be obliged to have recourse to some particular 

 process. 



By boiling the finely divided earth in water, we can 

 separate from it all the soluble salts it contains, and the 

 evaporation of the liquid, which holds them in solution, 

 will enable us to know their natures and proportions. 

 If the operation be carefully conducted, the salts can be 

 obtained in crystals, and, by the character of these, 

 their properties can be distinguished. Nitre has a sharp 

 taste, and consumes upon glowing charcoal ; marine salt 

 decrepitates, and splits with a sparkling appearance over 

 the fire ; the sulphate of soda swells up with the heat, 



