f)S4 L'RINCll'LKS 01.' rllKMJSTKY 



crvstalline magnesium carbonate is termed magiiesitt 3 . The formation 

 of the crystalline varieties of the insoluble carbonates is explained by 

 the possibility of a slow deposition from solutions containing carbonic 

 acid. Besides which the calcium and magnesium sulphates art 1 obtained 

 fnnn sea water, and therefore thev are met with both a^ deposits and 

 in springs. It must be observed that magnesium is held in considerable 

 quantities in sea water, because the sulphate and chloride of magne- 

 sium are very soluble in water, whilst calcium sulphate is but little 

 >oluble; and therefore if the occurrence of considerable deposits of 

 magnesium sulphate cannot be expected in nature, still, on the other 

 hand, one would expect (and they do actually occur) large masses of 

 calcium sulphate or //////>/////. < 'aS< ) ( .'2 1 1 .,< '. (Jypsum sometimes forms 

 strata of immense si/.e, which extend over many tens of kilometres - 

 for example, in llu.ssia on the Volga. and in the Donetx and Ualtic 

 pn >vince>. 



Lime and magnesia also, but in much smaller (quantities (often to 

 the amount of several fractions of a per cent, and rarely more), enter 

 !/{fn f//>. I'OinjinxltiuH of everv fertile NO/'/, and without these bases the 

 >oil is tmable to >upport vegetation. Lime is particularly important 

 in this re>pect, and its ]iresence in a larger quantity generally improves 

 the harvest, although purelv calcareous soils are generally infertile. 

 Kor this reason the soil is fertilised both with lime 1 - itself and with 

 marl that is. with clay mixed with a certain quantity of calcium carbo 

 nate. strata of which are found nearlv everywhere. 



I'Yom the >oil the lime and magnesia (in a smaller quant itv) pass 

 into the substance of jilxufs^ where thev occur as salts. Certain of 

 these -alts separate in the interior of plants in a crystalline form for 

 example, calcium oxalate. The lime occurring in plants serves as the 

 source for the formation of the \ariou-, calcareous secretions which arc 

 so ei immoii in dii'iniii /N of all classes. The bones of the highest animal 

 orders, the she] I- < it' mollusca, the covering of the sea-urchin, and similar 

 solid secretions of sea animals, contain calcium salts; namely, the 

 shells mainly ;i]eiiim carbonate. ;md bones mainly calcium phosphate. 

 (Vrtain lime-tones are almost entirely formed of such deposits. 

 Odc-sa is situated on a limestone ot' this kind, composed of shells. 

 Thus magnesium and calcium occur throughout the entire realm of 

 nat ure. 



ihilaUc action ni linn' in increasing tip- I'crtilitv of soil-; if not in every 

 il . with ordinary -.oils which have lon^ l.ccn under corn i:-; lia-ed not so 

 i|iiirenients "I plants for tip' linn' it -< -It .1 - mi those chemical and physical 



