No. 6. DEPARTMENT OP AGRICULTURE. 399 



cudeavor 1o briug iuto this pai)er, so far as time will permit, a brief 

 mention of the results of the more recent investigations of this sub- 

 ject; so that the paper may be considered as a condensed supplement 

 to the bulletin I sometime since wrote for the Department. 



Lime is the name applied to the white solid top when limestone is 

 heated for a long time at a high temperature. By this process the 

 lime is split into two parts — a gas, carbonic acid, which constitutes 

 44 per cent, by weight of a perfectly jjure, dry limestone, and which 

 escapes into the air; and lime, which constitutes in such limestone, 

 50 per cent, of the original weight. This white residue, lime, is not, 

 however, a simple or elementary substance, but can be, in time, split 

 by appropriate chemical methods into two elementary materials. 

 One, oxygen, the less abundant of the two principal components of 

 the air; the other, bright, yellowish calcium. Because of these facts, 

 pure limestone is called by the chemist carbonate of lime, or calcium 

 carbonate, while lime itself is scientifically termed calcium oxid. So 

 eagerly does metallic calcium seize upon oxygen that it burns with 

 intense light when heated in air, and can be preserved only by care- 

 ful protection from moisture. Lime or calcium oxid bears to the ma- 

 tallic calcium the same relation that iron rust and common iron ore 

 have to metallic iron. This oxid, too, is difficult of preservation be- 

 cause of its strong tendency to unite with water to form calcium 

 hydrate or slaked lime, and with the carbonic acid, which is ever 

 present in the air, to form calcium carbonate. Air-slaked lime is a 

 mixture of true lime, calcium hydrate and calcium carbonate. 



Neither the metal calcium nor its oxid, lime, occurs in nature in 

 free condition, except it is artificially produced, it is found in com- 

 bination with acids, chiefly with silica and carbonic acids in rocks, 

 with these and nitric and tannic acid in soils, with sulphuric acid in 

 gympsum, with this and hydrochloric acid in mineral and sea waters, 

 and with phosphoric, carbonic and organic acids in plants and ani- 

 mals. 



Its importance to the farmer is found in these facts: That it has 

 important relations to the living plants and animals with whose pro- 

 duction be is concerned; that it is capable of producing extensive 

 physical alterations in the soils of the farm; and, finally, that it is 

 the cheapest, strong chemical agent of a wide variety of forms that 

 the farmer applies in his laboratory, the soil. 



Lime is essential not only to the highest productiveness but to 

 the very existence of the plants cultivated on the farm; furthermore, 

 not an organ or a tissue in their entire structure is without this con- 

 stituent in one or another state of combination and degree of use- 

 fulness. The proportion usual in different growths differ greatly 

 from one another, it is true; a crop of clover removes ten times as 

 much as a crop of wheat or rye, and six times as much as a crop of 



