202 MAGNE3IUM,%ND CHLORIDE OF MAGNESIUM. 



vegetable physiology, yet if lime and magnesia have the power of dif- 

 ferently afiecting the animal economy, why may they not also very 

 differently adect the vegetable economy ? And since in the same cir- 

 cumstances, and in combination with the substances they meet with 

 in the same soils, magnesia is capable of entering more largely into 

 a plant by its roots — may not magnesia be considered capable of poi- 

 soning a plant, when lime in the same condition would only improve 

 the soil ? 



I have said that it may be doubted whether magnesia in the state of 

 carbonate is wholly unhuriful to the land. This doubt rests on the fact 

 that the magnesia retains its carbonic acid more feebly than lime does 

 — and therefore its carbonate is the more easily decomposed when an 

 acid body comes in contact with both. Though, therefore, the mag- 

 nesian carbonate will not lay hold of all acid matter so readily and surely 

 as caustic magnesia may, still occasions may occur where acid matters 

 being abundant in the soil, so much carbonate of magnesia may be de- 

 composed and dissolved as to render the water absorbed by its roots 

 destructive to the health or life of a plant. 



In reference to this point, however, it must be distinctly understood, 

 that magnesia is one of the kinds of inorganic food most necessary to 

 plants, that a certain quantity of it in the soil is absolutely necessary to 

 the growth of nearly all cultivated plants, and that it is only when it is 

 conveyed to the roots in too large a quantity, that it proves injurious to 

 vegetable life. 



5°. Magnesium is the metallic basis of magnesia. Little is known 

 of its properties, owing to the difficulty of preparing it in any consider- 

 able quantity for the purpose of experiment. It is a white metal, which, 

 when heated in the air, takes fire and burns, combining with the oxygen 

 of the atmosphere, and forming magnesia. It is not known to occur in 

 nature in an elementary form, and therefore is not supposed directly to 

 influence vegetation. 



6°. Chloride of Magnesium. — When calcined or carbonated magne- 

 sia is dissolved in muriatic acid, and the solution evajwrated to dryness, 

 a white mass is obtained which is a chloride of magnesium, consisting of 

 magnesium and chlorine only. This compound occurs not unfrequently 

 in the soil, associated with chloride of calcium. It is met with also in 

 the ash of plants, while in sea water, and in that of some salt lakes, it 

 exists in very considerable (juantity. Thus 100 parts of the water of 

 the Atlantic have been found to contain 3i of chloride of magnesium, 

 while that of the Dead Sea yields about 24 parts of this compound.* 

 Hence it is present in great abundance in the mother liquor of the salt 

 pans, and it is from the refuse chloride in this liquor that the magnesia 

 of the shops, as above stated, is frequently prepared. 



The chloride of magnesium has not hitherto been made the subject of 

 direct experiment as a fertilizer of the land. From the fact, however, 

 that plants require much magnesia and some chlorine, there is reason to 

 believe that, if cautiously applied, it might prove beneficial in some soils, 

 and especially to grain crops. Its extreme solubility in water, however, 

 suggests the use of caution in its application. The safest method is to 



* 100 parts of the water of the Dead Sea contain also about lOJ of chloriUfi jpf p^l&iumi 

 and nearly 8 of common salt. ' ' ": ;.' "^ ^y ^•^' ' 



