183 



Scientific A griculfurr. 



cases whore the distance of railway transportation or of cartage is great. One 

 hundred pounds of such lime usually contain about 95 pounds of actual Lime. 

 Sometimes burned lime contains considerable magnesia, a point which has already 

 been considered. 



According to Roberts, " when first moved from the kiln, lime weighs about 

 75 pounds to the heaped bushel ; that from shells weighs less than that from lime- 

 stone. A ton of limestone converted into caustic lime (CaO) weighs between 1,100 

 and 1,200 pounds ; hence it is economy to burn the lime near where the stones are 

 quarried, since it weighs but three-fifths as much as limestone. In slaking, lime 

 takes up considerable quantities of water ; hence a ton of slaked or hydrated lime 

 contains really but three-fourths as much lime as a ton unslaked. A heaped bushel 

 of unslaked lime makes H bushels of slaked lime;* therefore it should be trans" 

 ported before it is slaked. When caustic lime is exposed to the air for some time 

 it absorbs both moisture and carbon dioxid from the atmosphere and becomes 

 air-slaked lime. By still longer exposure it may all change into carbonate of lime, 

 the same form as before burning. It is, however, much finer than ground limestone." 

 Lime made from oyster shells and magnesian limestone Aveighs less per bushel 

 than that made from the purer kinds of limestone. 



Gypsum, or Land Plaster, is a co mbination of lime with sulphuric acid 

 (oil of vitriol) and water. Upon heating, gypsum loses its water and is changed into 

 plaster of Paris or calcined plaster, which is used in making casts and for many 

 other industrial purposes. 



In case a soil is seriously deficient in lime, gypsum may act as a direct 

 manure ; usually, however, its beneficial effect upon soils is attributed to its indirect 

 action in liberating potash, and possibly other substances, which were locked 

 up in the soil in such combinations that plants could not make use of them. Gypsum 

 may be helpful to a limited extent on clayey soils by flocculating the fine particles, 

 on account of which the soil is less likely to become "water-logged" and to cake, 

 and hence interfere Avith the operations of tillage. In the last-mentioned respect 

 water-slaked lime or the carbonate is said to be much more efficacious than gypsum ; 

 though as a liberator of potash gypsum is claimed to lead. 



It is stated on good authority that, in the presence of decaying organic 

 matter, gypsum may be changed into carbonate of lime. While this may be true 

 under certain circumstances, in experiments at the Rhode Island Station on a soil 

 exceptionally rich in humus and containing a moderate amount of plant residues 

 which were undergoing decomposition, such a change did not result, if at all, to a 

 practical extent. For this reason and on account of the fact that gypsum contains 

 only about one-third as much lime as burned lime, and usually costs as much or 

 more per ton, it cannot take the place of the latter for most of the purposes for 

 which lime is applied to land. 



For use in renovating " black alkali " (sodium carbonate) soils in the arid 

 regions, gypsum, as already explained, performs a valuable function which can 

 not be filled by any of the other compounds of lime. 



Chalk is a naturally occurring form of carbonate of lime which is excep- 

 tionally pure. It is quite soft, and is frequently referred to as marl. 



Marl is a name which is applied to earthy deposits usually more or less 

 friable in their character and containing carbonate of lime in quantities ranging 

 usually from 5 to 95 pounds per 100 pounds of the material. It must be evident, 

 therefore, that if one intends to make use of a given deposit of marl for the lime 

 contained in it, he should first have a sample of it analyzed.t If the material will 



* A bushel of air-slaked lime is usually considered to weigh 50 pounds, 

 t The Experiment Stations in the different States would probably undertake to do this 

 free of cost. 



