MANURES. 49 



and vigorous growth to most seeds, besides securing them 

 from the depredation of insects and marauders of various kinds. 

 This enables them rapidly to push forward their roots, stems 

 and leaves ; thus obtaining a greater range for the roots, and 

 more mouths for the leaves to draw their nourishment from 

 the atmosphere, by which vegetation is accelerated, and 

 where the period for maturity is limited, materially increasing 

 the product. 



CARBONATES, NITRATES, SULPHATES, PHOSPHATES, SILICATES, 

 AND CHLORIDES. 



Several of these have just been particularly enumerated. 

 The remainder are composed of carbonic, nitric, sulphuric 

 and phosphoric acids, silica and chlorine, in chemical com- 

 bination with potash, soda, lime and the other bases or 

 ash of plants. Although no one of these can fail to benefit 

 crops, when rightly applied, yet the expense of most of 

 them, will prevent their extended use. This can only be 

 looked for, from those which are procurable at a cheap rate. 

 The chemical laboratories, glass works, and some other 

 manufactories, afford in their refuse materials, more or less 

 of these mineral manures, which would well repay the 

 farmer for removing and applying to his land. The most 

 obvious that occur in this country, are all that will be here 

 mentioned, 



OLD PLASTER. 



This is a true silicate of lime ; being formed mostly of 

 siliceous sand and lime, chemically combined. For mea- 

 dows, and for most other crops, especially on clays and 

 loams, this is worth twice its weight in hay ; as it will pro- 

 duce a large growth of grass for years in succession, and 

 without other manure. This effect is due, not only to the 

 lime and sand, but to the nitric acid which they have ab- 

 stracted from the atmosphere, and which they continue 

 alternately (while in combination) to absorb from the air 

 and give out to the growing plant. But the farmer cannot 

 too carefully remember, that with this, as with all other 

 saline manures, but a part of the ingredients only is thus 

 supplied to vegetables ; and without the addition of the 

 others, the soil will sooner or later become exhausted. 



BROKEN BRICK AND BURNT CLAY. 



These are composed mostly of silicate of alumina, but they 

 are generally mixed with a small quantity of silicate of pot 

 3 



