NITRATE, SULPHATE, AND niOSPHATE OF MAGNESIA. 203 



dissolve it in a large quantity of water, and to apply it to the young 

 plant by means of a water-cart. In this way the refuse of the salt 

 works miglit, in some localities, be made available to useful purposes. 



Tlie chloride of magnesium is decomposed both by quick-lime and by 

 carbonate of lime ; hence when applied to a soil containing lime ip 

 either of these states, chloride of calcium and caustic or carbonated mag 

 nesia will be produced. 



7°. Nitrate of Magnesia is formed by dissolving carbonate of magne- 

 sia in nitric acid, and evaporating the solution. It attracts moisture from 

 the air with great rapidity, and runs into a liquid. It is probably formed 

 naturally in soils containiftg magnesia, in the same way as nitrate of 

 lime is known to be produced in soils containing lime. [See Lecture 

 VIII., p. 159.] No direct experiments have yet been made as to its 

 effects upon vegetation ; but there can be no doubt that it would prove 

 liighly beneficial, could it be procured at a sufficiently cheap rate to ad- 

 mit of its economical application to the land. 



8°. Sulj)hate of Magnesia — the common Epsom salts of the shops — 

 is formed by dissolving carbonate of magnesia in diluted sulphuric acid. 

 It exists in nearly all soils which are formed from, or are situated in, 

 the neighbourhood of rocks containing magnesia. In some soils it is so 

 abundant that in dry weather it forms a while efflorescence on the sur- 

 face. This has been observed to take place in Bohemia, Hungary, and 

 parts of Germany, and it may be frequently seen in warm summer 

 weather in the neighbourhood of Durham.* 



This salt has been found by Sprengel to act upon vegetation precisely 

 in the same way as gypsum does, and on tlie same kind of plants. It 

 must be used, however, in smaller quantity, owing to its great solubili- 

 ty. Its higher price will prevent its ever being substituted for gypsum, 

 as a top-dressing for clover, &c., but it is worth the trial, whether corn 

 ))lants, the gtain of which contains much magnesia, might not be bene- 

 fitted by the application of a small quantity of this sulphate — along with 

 such other substances as are capable of yielding the remaining constit- 

 uents which compose the inorganic matter of the grain. Its price is not 

 too high to admit of this more restricted application. f 



9°. Phosphate of Magnesia. — Magnesia exists in combination with 

 phosphoric acid, in the solids and fluids of all animals, though not so 

 abundantly as tlie phosphates of lime. In most soils phosphate of mag- 

 nesia is probable present in minute quantity, since in the ashes of some 

 varieties of grain it is found in very considerable proportion. 



Its action upon vegetation has never been tried directly, but as it 

 exists in urine, and in most animal manures, a portion of their efficac^)^ 

 may be due to its presence. In turf ashes, which often prove a valua- 

 ble manure, it is sometimes met with in appreciable quantity, and their 

 beneficial operation in such cases has been attributed in part to the agen- 

 cy of this phosphate. 



' It occasionally collects beneath the plaster of old walls in Durham. In one of the lower 

 rooms of the old Exchequer buildings, I found it forming an extensive layer nearly half an 

 inch thick, beneath the damp plaster. The magnesia is derived from the magnesian lime- 

 stone, used both for mortar and for building stone. 



t Its price in Newcastle in the state of crystals, is about 10s. a cwt. The impure salt col- 

 lected at the alum works on the Yorkshire coast, might be obtained, I should supj ose, for 

 little more than half this price. 



