132 LESSONS m CHEMISTRY. 



insist upon being supplied with an analysis, such as above 

 given, in which the amount of phosphates and ammoniacal 

 compounds, with the quantity of ammonia which they are 

 capable of yielding by decomposition, is clearly stated. 

 These are the substances which it would cost the farmer 

 most to purchase in the manure market, and their amount 

 in a sample of guano, may be taken as representing its 

 actual value. 



195. Bones. — At the present time bones are even more 

 extensively employed than guano for manuring. Their 

 reputation has progressed with the extension of the turnip 

 husbandry, and their use has, in no small degree, contributed 

 to improve the agriculture of districts which, from being 

 inaccessible to the more bulky manures, were formerly re- 

 garded as hopelessly barren. 



196. For many years, crushed bones have been regarded 

 by the English farmer as his most valuable fertilizer ; and by 

 their appUcation alone, the fields of Cheshire, and other coun- 

 ties, exhausted by producing substances rich in phosphates, 

 as milk and cheese (54), had their ancient fertility restored. 

 In both England and Scotland, their importance is at present 

 very generally acknowledged. It is stated by a weU-informed 

 authority, that one-third of the whole turnip-crop of these 

 countries depends upon them. In Ireland, though within the 

 last two or three years, there has been a considerable exten- 

 sion of their use among the more inteUigent farmers, yet a 

 large bulk of the bones collected in this country are purchased 

 by the Scottish farmer ; and thus our fields are exhausted, 

 not only by the cattle which are fed upon them for the Eng- 

 lish market, but by the loss of the compounds of phosphorus, 

 which the crushed bones that we export contain. 



197. Composition of Bones. — Like the plants upon which 

 the animal feeds, and from which, it is evident, all the mate- 

 rials for its growth must have been derived, bones consist of 

 two parts — a part which disappears into the air when they 

 are exposed to a strong heat, in the open fire, and an in- 

 combustible ash which remains. In the plant, the combusti- 

 ble or organic part, constitutes by far the largest portion of its 

 bulk. The ash left by burning a hundred weight of turnips 

 would weigh only about three-fourths of a pound ; but when 

 bones are burned, the ash weighs more than the combustible 

 matter which disappears. Bones difler in density, and in the 



