Composition and Value of Guano. 223 



cake is 46 per cent. The proportion of phosphoric acid and of 

 potash furnished bv a ton of oilcake, although worthy of consi- 

 deration under other circumstances, is too small to affect to any 

 considerable extent the present calculations (see note in Appen- 

 dix). At 46 per cent, a ton of oilcake will contain 103 lbs. of 

 nitrogen, capable of becoming 125 lbs. of ammonia. Taking 

 oilcake at 61. lOs. a ton as a low price, and IIZ. as the other ex- 

 treme, the ammonia will cost as follows: — At 6Z. IO5. a ton the 

 ammonia will cost Is. O^d. per lb. ; at 1 IZ. a ton the ammonia will 

 cost Is. 9d. per lb. Considered, then, in the light of manure 

 onli/, oilcake must at its minimum price be a dear source of 

 ammonia. 



Rape- cake is as nearly as possible of the same composition as 

 linseed-cake, its cost being, however, only from 4Z. to 5Z. a ton. 

 At 4Z. \0s., the mean of these numbers, ammonia as supplied by 

 rape-cake would cost about 8|tZ. per lb. 



Of the price of ammonia as derived from bones we have be- 

 fore incidentally spoken. From this source a supply of ammonia 

 will be obtained at a price ranging between 4\d. and 6d. per lb., 

 according as the value of phosphate of lime is estimated at Jc?. or 

 |c?. per lb. As the latter sum has been shown to be a fair price 

 for the earthy phosphates, it may be assumed that ammonia is 

 bought rather more cheaply in bones than in sulphate of am- 

 monia, but with the essential difference that in the case of bones 

 the ammonia has to be formed — we must wait for it. How great 

 an advantage this is in favour of the ready-made (so to speak) 

 ammoniacal manures in certain soils, those readers who rightly 

 estimate the value of time in relation to practical agriculture will 

 easily perceive. 



There are yet other sources of ammonia within the reach of the 

 farmer ; and it might be thought that these should be referred to 

 as a guide to its money value. Woollen rags, clippings of skins, 

 parings of horns and hoofs, dried blood, seal-skins, &c. — all or 

 any of them may under peculiar circumstances with great advan- 

 tage be employed by the farmer. As, however, the supply of 

 such refuse substances is limited, and as, for want of the more 

 uniform demand which an unlimited supply would infallibly 

 create, the price is a matter of perfect caprice, it would be unsafe 

 to draw any very general conclusions from the imperfect data so 

 obtained : individuals may and do buy these nitrogenous sub- 

 stances for manure with great advantage to themselves, but the 

 community of agriculturists could not do so. 



We shall reserve the question of the cost of ammonia in 

 guano itself until we have fixed the price of potash — the only re- 

 maining datum needed for ascertaining the value of different 

 specimens of the manure in question. 



