40 



THE COMMERCIAL AND AGRICULTURAL 



and the circumstances which principally determine the value of 

 superphosphate of lime. In the following Table is stated the 

 composition of four different samples of guano, all professedly 

 Peruvian guano : 



COMPOSITION OF GUANO. 



The two first-mentioned samples are genuine Peruvian guanos 

 of excellent quality. The third is Peruvian guano of an inferior 

 description ; the large amount of siliceous matter arises no doubt 

 from the rock having been too closely scraped in collecting it. 

 The fourth, though sold as Peruvian, appears to be in reality a 

 Saldanha-bay guano of medium quality. 



Considerable differences thus occur in the composition of 

 different samples of guano, sold as the above four samples, at 

 the same prices. 



It is well to remember that the chief value of guano depends 

 upon the amount of ammonia which it is capable of furnishing, 

 and not upon that of phosphates and alkaline salts. A good 

 Peruvian guano should contain from 50 to 60 per cent, of organic 

 matter, yielding at least 16 per cent, of ammonia, 20 to 25 per 

 cent, of bone-earth, 6 to 8 per cent, of alkaline salts, and no more 

 than 2 per cent, of insoluble siliceous matter (sand). 



On burning genuine Peruvian guano it loses about two-thirds 

 in weight, and leaves one- third of its weight of a perfectly white 

 ash, which does not effervesce with an acid ; whilst adulterated 

 guano generally produces on burning a much larger quantity of a 

 reddish coloured ash, or a white ash, which either does not readily 

 dissolve in dilute acid (showing the adulteration with gypsum), 

 or strongly effervesces with an acid (proving the adulteration 

 with chalk). 



Genuine Peruvian guano, moreover, weighs from 68 to 72 Ibs. 

 per bushel ; whilst adulterated guano weighs considerably more, 

 no cheap material having been discovered with which guano can 

 be readily adulterated without increasing its specific gravity. 



In purchasing Peruvian guano it is by no means necessary to 



