152 LESSONS IN CHEMISTRY. 



improve its qualities, and apply the mixture with great 

 advantage to the flax-crop. In England, rape-dust is applied 

 at the rate of from 8 to 16 bushels per acre, and is usually 

 sold at about £7 per ton. 



235. The husk of the oat^ malt-dust, and the hran of 

 wheat, may all be used with advantage as manures, and 

 should be economized by the farmer. Wheat bran, especially, 

 sliould be regarded as a valuable fertilizer, being rich in both 

 nitrogen and saline matters. It has been used with remark- 

 able effect in England.* Added to tlie manure heap, and pro- 

 perly preserved from excessive fermentation, all these vege- 

 table substances will be found useful applications to the soil. 



236. It may be useful for you to recollect, in considering 

 the effects which the various animal and vegetable substances 

 employed as manures, are capable of producing, that the 

 immediate effects which may be expected to follow their 

 application will depend chiefly upon the amount of matters 

 capable, by their decomposition, of yielding ammonia, which 

 they contain, while the permanence of then- action will depend 

 upon the amount of inorganic mattei-s, and especially of the 

 phosphates of lime and magnesia. 



237. Mineral and saline manures. — Formerly it was ima- 

 gined that the only substances capable of supplying food to 

 plants were those derived fi'om animals and vegetables; and 

 though, in various parts of the world, lime, marl, gypsum, 

 saltpetre, and other mineral and saline matters, dug out of 

 the earth, had been used with extraordinary success in in- 

 creasing the fertility of the soil, yet it was considered that 

 these substances were not true manures, but merely in some 

 unknown manner stimulated plants to consume larger quan- 

 tities of the food supplied in the soil, and, in consequence, 

 accelerated its exhaustion, " enriching the fathers while they 

 impoverished the sons." The progress of agricultural che- 

 mistry has, however, given us more correct opinions with 



* Professor Johnston gives the following as the average composition 

 of the bran of wheat : — 



Water 13-1 



Albumen coagulated 19-3 



Oil 4-7 



Husk, and a little starch 55"6 



Saline matter 7*3 



100 



