§ no. LIMESTONE AND LIME. 209 



LIMESTONE AND LIME. 



110. a. If it is desired to examine the changes that a 

 limestone has midergone in weathering, or to ascertain 

 what it contains tliat may contribute to the fertility of 

 the soil, it should, of course, be taken in its natural, air- 

 dry, unignited condition. 



Pulverize it, and treat from 150 to 300 grms., according 

 to the proportion of clay or other silicates present, Avith 

 cold and liot concentrated hydrochloric acid, with sul- 

 phuric acid, and so on, in the manner directed for the 

 analysis of soils. The cold hydrochloric acid dissolves 

 all the carbonates, commonly all the phosphoric acid, but 

 only a small portion of the alkalies, even if a considerable 

 amount of these is present. But this small quantity that 

 is taken into solution should be determined, and the esti- 

 mation can be eifectecl, after removal of the silica, in the 

 usual manner (Scheme I., « or J, § 94). 



The residue, insoluble in cold hydrochloric acid, is of 

 great importance, agriculturally considered, for it is not 

 seldom rich in potassa, and it should be examined with 

 the aid of the silt analysis, as well as of hot hydrochloric 

 acid, sulphuric acid, and hydrofluoric acid (§ § 101, 102, 

 103). In one case, over 50"|gOf potassic feldspar was 

 found in the sandy insoluble residue of a dolomitic lime- 

 stone ; in another case little but pure quartz. 



h. By " burning " the limestone, it Is essentially changed 

 with respect to the solubility of its constituents, and j)ar- 

 ticularly the alkalies, which become soluble in larger 

 measure. Therefore, when a limestone is to be applied to 

 the soil after being burned, it should be burned before 

 being analyzed ; this may be accomplished by igniting it 

 in a Hessian crucible through the bottom of which a hole 

 has been broken, until, after cooling, a piece of it falls 

 completely to a fine powder when moistened with about 

 a third of its weight of water. 



