VEGETABLE MANURES. 153 



respect to the action of these substances, and has sho^vn us 

 that, like the inorganic matters contained in the ashes of sea- 

 weeds and peat, and in the excrements of animals, they increase 

 the produce of the soil, because they supply it with some of 

 the materials indispensable to the growth of plants. 



238. From the information which you have acquired, yon 

 will find no difficulty in understanding why the application 

 of one kind of mineral or salme matter should occasionally 

 disappoint the expectations of the farmer; why gypsum should 

 promote the growth of the crops in one district, and produce 

 no effect in another part of the country; or why lime or 

 marl should, after a number of years, cease to insure a fertile 

 return, and seem even to injure the land. You are aware 

 that it is only in proportion as you place in the soil the 

 materials taken away in cultivation that you can expect 

 to maintain its productiveness ; that lime or nitrate of soda, 

 or saltpetre, will be sufficient to enable it to yield crops only 

 when the eight or nine other substances which are discovereil 

 in the ashes of your crops are already present in sufficient 

 quantities ; and that if, year after year, you carry away in 

 your crops several of these substances, and replace only one 

 or two of them in the manures which you apply, exhaustion 

 must sooner or later be expected to occur. 



239. Artificial manures. — The striking effects which at- 

 tended the use of guano and bones, which led the most 

 sceptical to admit that bulk was not indispensable to the 

 efficacy of manures; and the information which chemists 

 communicated, that the materials from which these substances 

 derived their fertilizing power were the same that existed in 

 fertile soils, and in the ashes of plants, suggested the possi- 

 bility of compounding mixtures adapted to the special wants 

 of the various crops cultivated by the farmer; and within 

 these few years so great has become the demand for these 

 artificial compounds, that a new and important trade has 

 been created in preparing them. In England and Scotland, 

 at the present time, enormous quantities of mineral sub- 

 stances and chemical compounds are used as manures: of 

 sulphuric acid alone, it is said that last year as much as 

 1 27,750 lbs. were consumed by the farmers in one agricultural 

 district in Yorkshire. 



240. I have already, in Chapter III. described to you the 

 leading characters of the mineral and saline matters which are 



