46 



CHYMISTRY APPLIED TO AGRICULTURE. 



they are calcareous, acids will dissolve them, producing 

 at the same time an effervescence ; to prove this, a fev\^ 

 grains of them maybe put into a glass containing good 

 vinegar, or muriatic acid diluted with three or four parts 

 of water ; if they are composed only of carbonate of lime, 

 they will be entirely dissolved, especially if the liquor 

 should still preserve its sharp and sour taste; for in all 

 these experiments it is necessary to use an excess of acid. 



If the coarse particles do not effervesce with an acid, 

 they are composed entirely of silica or alumina. These 

 are easily distinguished from each other, the silica being 

 rough to the touch, scratching glass, and sinking quickly 

 in water ; whilst alumina is smooth and unctuous to the 

 touch, and mixes with water, in which it remains some 

 time suspended. 



The coarse particles may be composed by the union of 

 the calcareous, siliceous, and aluminous earths; but in 

 this case the acids have dissolved a part of the calcareous 

 particles ; and, after removing the acid which holds them 

 in solution, it is easy to ascertain by the abovementioned 

 characteristics, whether the insoluble portion remaining 

 in the glass be silica or alumina. 



If the coarse particles are only of quartzeous sand or 

 of pure silica, water and the acids will produce no effect 

 upon them ; and their nature can be easily determined 

 by the characteristics I have given of silex and alumina. 



It sometimes happens that these coarse particles are 

 mixed with the remains of animal' or vegetable substances 

 imperfectly decomposed ; but these will be easily recog- 

 nized by the characteristics which distinguish fossil sub- 

 stances. 



Nothing now remains to be done but to examine the 

 finely divided and pulverulent soil, which passed through 

 the sieve ; this contains the earths, salts, and animal and 

 vegetable substances, in a state of minute division. In 

 order to ascertain the nature and proportions of the prin- 

 ciples contained in this mixture, it must be first weigh- 

 ed, and then boiled in four times its weight of water, 

 from ten to fifteen minutes ; the whole should then be well 

 stirred, and left to settle ; a precipitate will soon be 

 deposited, consisting only of the heaviest portions of the 

 mass, usually of fine siliceous sand ; the turbid liquor 

 which floats above being thrown on a filter, the earths 

 and some salts not easily soluble remain upon the filter, 



