L1MK. 493 



therefore generally thrown down as oxalate, and afterwards ob- 

 tained as carbonate of lime, by heating the oxalate nearly to 

 redness in a platinum crucible, in which a small fragment of 

 carbonate of ammonia is dissipated at the same time, to prevent 

 any lime becoming caustic by loss of carbonic acid. 



Lime is applied to a variety of useful purposes in ordinary 

 life and in the arts, of which the most important are its appli- 

 cations as mortar and as a manure for land. In the last, lime 

 does not act as an aliment of plants, but is useful in accelerating 

 the decomposition of the insoluble organic matter which soil 

 contains, and thereby rendering it capable of sustaining vege- 

 table life. Hence, the extraordinary fertility which lime deve- 

 lopes in soils containing peaty matter. In the formation of 

 mortar, the hydrate of lime is mixed with 2 parts of coarse, or 

 3 parts of fine sand, and made into a paste with water. In 

 building, a stone is laid upon a bed of this paste, which it 

 compresses by its weight, imbibing moisture also from the 

 mortar, which escapes principally through the porous stone. 

 On drying, the mortar binds the stones between which it is 

 interposed, and its own particles cohere so as to form a hard 

 mass, solely by the attraction of aggregation, for no chemical 

 combination takes place between the lime and sand, and the 

 stones are simply united as two pieces of wood are by glue. 

 The sand is useful in rendering insignificant by its mass the 

 contraction of the mortar on drying, and also, from the large 

 size of its grains, in rendering the dry mortar less short and 

 friable. The mortar is subject to an ulterior change, from the 

 slow absorption of carbonic acid, but even in the oldest mortar, 

 the conversion of the hydrate of lime into carbonate is never 

 complete. 



Some limestones, containing about 20 per cent of clay or 

 silicate of alumina, afford lime which possesses a valuable pro- 

 perty, that of forming with water a mass which becomes solid 

 in a few minutes, and therefore hardens in structures covered 

 by water. An excellent hydraulic mortar of this kind is ob- 

 tained from concretionary masses found in marie, and also 

 as isolated blocks in the bed of the Thames. This lime being 

 burnt, ground and sifted, when mixed with water to form a 

 paste, sets as quickly as Paris plaster ; its solidity increases with 

 the time it has been submerged, and it ends by acquiring the 

 hardness of limestone. Sand is added to it when it is used 



