Composition and Value of Guano. 205 



Having: now before us the analyses of nearly 50 specimens 

 of Peruvian guano, we may very safely proceed to draw from 

 them some general conclusion as to its average composition, and 

 as to the extent of deviation to which that composition is liable. In 

 doing so, perhaps the fairest plan will be to take first into consi- 

 deration those specimens only which have been obtained directly 

 from the docks. 



The Tables 2, 5, and 6, give the composition of 32 specimens, 

 concerning whose history there is no doubt. 



The first ingredient to be noticed is the Water. — Although to 

 all appearance guano is frequently quite dry, this is not che- 

 mically the case. A certain quantity of water is natural to it, 

 being absorbed by the compounds which it contains ; and even 

 when taken from the centre of a cargo, and quite dusty in character, 

 guano yet contains about one-tenth part of its weight of water. 

 It has also a strong tendency to absorb moisture from the air, 

 and to this circumstance is due the change of colour which it 

 undergoes when left exposed for a short time. 



The drier Peruvian guano is the lighter is its colour ; a brown 

 or chocolate tinge is not necessarily a proof of inferiority, inas- 

 much as this colour is often due to its having become accidentally 

 damp. With a knowledge of this disposition to attract moisture 

 from the air, we are not surprised to find the different specimens 

 exhibiting some latitude in the amount of water. 



The lowest per centage of water (Spec. 3) . is . 8'88 

 The highest „ „ (Spec. 4) . „ . 22-68 

 The average of 32 specimens being 13-09 



It will be observed that those most recently examined (Table 6) 

 are all of them drier than those which were imported at an earlier 

 period. I have no doubt that the excess of moisture in the 

 former is therefore due to exposure since the cargoes were un- 

 shipped, and that the average of the 5th and 6th Tables (which 

 is 12-14 per cent.), will express about the real proportion of mois- 

 ture. The water in guano is of no further interest than as, being 

 of no value itself, it depresses proportionably that of the guano. 

 Thus, for instance, the addition by accident or fraud of 5 or 10 

 per cent, of water to an originally dry specimen, will be a loss to 

 that amount on the farmer's purchase. At the same time it is to 

 be observed, that some of the wettest of the specimens of guano 

 in the table (as for instance. No. 5), are in no way inferior in the 

 proportion of ammonia, which, as will be presently shown, consti- 

 tutes its greatest value. 



This tendency to absorb moisture is worthy of a passing notice 

 in reference to the action of the manure ; for it is often of the 

 greatest consequence in dry seasons. 



Organic Matter and Salts of Ammonia. — When dried guano 



