200 



Composition and Value of Guano. 



In reference to this table, and passing by for the present the 

 proportion of water and organic matter, for the notice of which a 

 better opportunity will presently occur, we may observe that the 

 mineral value of guano would seem to consist solely in the phos- 

 phate and sulphate of lime and potash. Of soda there is very 

 little, except in the form of common salt, whilst the proportion of 

 magnesia is so small as hardly to deserve notice. 



It is an interesting and important fact that guano should con- 

 tain so much potash as is shown by this table to be the case : 

 that the proportion of the alkali is frequently as much as or 

 more than 3 per cent, of its weight is proved by the exami- 

 nation of other specimens. The following are the per-centages 

 of potash and soda in eight other samples of Peruvian guano, 

 of whose further composition we shall shortly have occasion to 

 speak : — 



Potash in 100 parts I 3-27 1 3-19 [ 3-43 j 4-60 I 3*43 I 3-74 I 6«49 I 3 73 

 Soda . . . . I 1-87 I -63 1 • 75 | none | 1 • 03 | -51 | -67 | '79 



Although the chlorine has not in these latter cases been deter- 

 mined, it is probable that, as in the other eight samples, the soda 

 principally occurs as common salt. I shall shortly point out that 

 potash is not always found to the same extent as in the tables ; 

 but my present purpose is to show that in guano the ingredients 

 of any value are few and simple. Reverting to the table, we find 

 that under the head of " Animal Matters and Salts of Ammonia" 

 is comprehended in most cases nearly one-half of the weight of 

 the guano. These animal matters are of value as manure, solely 

 in proportion to the ammonia which they can supply ; sooner or 

 later they pass into decomposition, giving rise to the usual pro- 

 ducts. It may be thought by some that as carbonic acid is one 

 of these products, and as it is well known that this gas is an agent 

 in vegetation, a certain allowance should be made for the car- 

 bonaceous elements. There is, indeed, no doubt that the more 

 dilute manures owe much of their efficacy to the compounds of 

 carbon, but these are always supplied in large quantity, whereas 

 the amount of carbonaceous manure furnished by a fair dressing 

 of guano is really too inconsiderable to be taken into account. 

 The " organic matters and ammoniacal salts," then, must be 

 valued only so far as they can supply ammonia. But it is to be 

 observed that part of these substances (as the carbonate and other 

 salts of ammonia) is capable of furnishing ammonia immediately; 

 whilst the other portion (the animal matter — the uric acid, for 

 instance) will require more or less time to become converted 

 into it, although to this point they will all eventually come. 

 Founded upon this circumstance some chemists have proposed to 

 distinguish the actually existing ammonia from that which will 



