218 



Composition and Value of Guano. 



monia being worth 3s., the remaining 2s. 6d. will here be consi- 

 dered as the cost of the phosphate of lime of 1 cwt. of bones. 



100 lbs. of bones contain 50 lbs., and 1 cwt. therefore 56 lbs. 

 of phosphate of lime. 2s. 6d. for 56 lbs. will give us rather more 

 than \d. per lb. as the price of the earthy phosphates of bones. 

 It is obvious that these two ingredients must bear the cost, between 

 them, and that, if we diminish the one, we must increase the other 

 in like proportion; thus, if we take 6d. a lb. as the ammonia 

 value of bones, the price of the earthy phosphates will be reduced 

 to one-third of a penny per lb. The sum of \d. per lb. seems a 

 very fair price to fix for the earthy phosphates of bones, and as 

 such it will be provisionally adopted. It now remains to calculate 

 by the same rule the cost of phosphate of lime in the cheaper 

 varieties of guano. 



In Saidanha Bay guano we buy both ammonia and phosphates ; 

 the former, however, in small proportion only. Taking for our 

 guide the averages given at p. 211, we find that Saidanha Bay 

 guano contains as a mean — 



Earthy phosphates . 55 • 00 per cent. 

 Ammonia .... 1*68 „ 



Saidanha Bay guano sells at from 41. 10s. to 51. a ton, more 

 usually the latter sum. The provisional price of 6d. a lb. for 

 ammonia, as before, will give the sum of 18s. to be deducted, 

 leaving the sum of 47. 2s. as the price of 1232 lbs. of phosphate 

 of lime, being at the rate of 100 lbs. for 6s. 7§e?., or a little more 

 than %d. per lb. In the preceding calculation the value of the 

 guano has been calculated with reference only to ammonia and 

 phosphate of lime, potash or other ingredients being left out as 

 needlessly complicating the question. 



Reviewing the subject of the last few pages, we find that the 

 approximative value of phosphate of lime ranges between %d. and 

 Id. a lb. 



Ammonia. — In endeavouring to fix the money value of ammonia 

 we must expect to meet with still greater difficulties than in the 

 case of the phosphates ; for whilst of the latter there are several 

 sources from whence a liberal and economical supply can be 

 drawn, it is really as a source of ammonia, pre-eminently so, that 

 guano possesses so high a manurial value ; and, consequently, 

 any attempt to attach a money value to the ammonia of guano, in 

 reference to that contained in other recognised manures, presup- 

 poses a degree of similarity in the economy of the substances thus 

 placed in competition, which is far from existing. Nevertheless, 

 it will be found that even in the case of guano the selling price is 

 to a certain degree in accordance with what it should be were the 

 substances which it contains to be furnished separately and from 



