CHAPTEE IX. 



MAGNESIUM CHLOIilDE — MAGNESIUM SULPHATE (EPSOM SALTS) — 

 MAGNESIUM BISULPHITE — iMAGNESIUM SILICATE (TALC SOAP- 

 STONE)— ALUM— ALUMINIUM SILICATE (CHINA CLAY)— ZINC SUL- 

 PHIDE— ZINC CHLORIDE— ZINC SULPHATE— ZINC BORATE— ZINC 

 SILICATE — ZINC FERROCYANIDE — ZINC SULPHOCARBONATE — 

 CADMIUM SULPHATE. 



51. Magnesium Chloride, MgClo. — Occurrence. — Naturally in 

 sea-water and as double salt in carnallite, KCl.,MgCl,„ in the Stassfurt 

 mines. 



Preparation. — By dissolving magnesia in dilute hydrochloric acid 



and evaporating the solution, the magnesium chloride is deposited as 

 crystals. 



Properties. — Very soluble in water, its taste is bitter. In medicine 

 it is used as a purgative ; it is more active than the sulphate of 

 magnesia. [Absorbs moisture from the air-deliquesces.] 



Action of Magnesia on Plants. — Magnesium salts are comprised 

 amongst the aUmentary substances indispensable to plants. Ch. 

 Dassonville found that plants watered with solutions of magnesium 

 chloride first suffered a retardation in their growth and sprung up more 

 rapidly afterwards. Loew states that a certain amount of magnesia 

 and lime is required in the soil to obtain a maximum crop. Goessel 

 made artificial cultures to fix these proportions with various amounts- 

 of these two oxides, and found that growth was at a maximum when 

 the media contained the lime and magnesia in the proportion of 0-4 to 1. 

 Katayama is of the same opinion as Loew in regard to the presence 

 in the soil of these two oxides ; he believes the ratio CaO : MgO as 2 : 1 

 as the most favourable for plants. Moller found that the absence of 

 magnesia in certain soils had a marked influence on the normal evolu- 

 tion of a plant. The pine, for example, suffers and its leaves turn 

 yellow at their extremities if it grows in a soil too deficient in magnesia. 

 It then suffices to water the tree with a solution of sulphate of magnesia, 

 or of chloride of magnesia, to re-establish the normal green coloration 

 of the leaves. The analysis of yellow leaves compared with those of a 

 normal green gave in the first case 0-279 per cent, in the second case 

 0-607 per cent magnesia. Towards strong doses in the soil plants 

 behave very differently. Steglich studied the action of magnesium 

 chloride on plants by watering alternately with a solution of 30 and 

 15 per cent, and at the end of his investigations prepared the following 

 table : — 



(160) 



