Elements of Agricultural Chemistry

by Thomas Anderson

6th, A bushel of the guano should not weigh more than from 56 to 60 lbs.

These characters must not, however, be too implicitly relied on, for they are all imitated with wonderful ingenuity by the skilful adulterator, and they are applicable only to Peruvian guano; the others being so variable that no general rules can be given for determining whether they are genuine. Neither are they so precise as to enable us to give any opinion regarding the relative values of several samples where all are genuine. The only way in which adulteration can with certainty be detected, and the value of different guanos be determined, is by analysis, and the importance of this can easily be illustrated.

In the table above, the average composition of the different guanos is given; but in order to shew how much individual cargos may differ from the mean, we give here analyses of samples of the highest and lowest quality of the genuine guanos of most importance:

	Angamos.		Peruvian.		Bolivian.
	Highest.	Lowest.	Highest.	Lowest.	Highest.	Lowest.
Water	12·60	7·09	10·37	21·49	11·53	16·20
Organic matter and ammoniacal salts	65·62	50·83	55·73	46·26	11·17	12·86
Phosphates	10·83	8·70	25·20	18·93	62·99	52·95
Alkaline salts	7·50	16·30	7·50	10·64	9·93	13·83
Sand	3·45	17·08	1·20	2·68	4·38	4·16
	100·00	100·00	100·00	100·00	100·00	100·00
Ammonia	25·33	17·15	18·95	14·65	1·89	2·23

The differences are here exceedingly large; and when the values of the two Peruvian guanos are calculated according to the method to be afterwards described, it appears that the highest exceeds the lowest in value by nearly £3 per ton. Of course, this is an extreme case, but it is no uncommon occurrence to find a difference of £1 or even £2 per ton between the values of cargos of Peruvian guano, which are sold at the same price.

The adulteration of guano is carried on to a very large extent; and though perhaps not quite so extensively now as it was some years since, it is only kept in check by the utmost vigilance on the part of the purchaser. The chief adulterations are a sort of yellow loam very similar in appearance to guano, sand, gypsum, common salt, and occasionally also ground coprolites and inferior guano. These substances are rarely used singly, but are commonly mixed in such proportions as most closely to imitate the colour and general appearance of the genuine article. The extent to which the adulteration is carried may be judged of from the following analyses taken at random from those of a large number of guanos, all of which were sold as first-class Peruvian.

Water	12·85	15·19	12·06	27·86	6·32
Organic matter and ammoniacal salts	26·84	44·31	34·14	30·41	27·42
Phosphates	15·54	20·95	22·08	22·17	33·61
Sulphate of lime	...	...	11·08	...	22·11
Alkaline salts	6·07	9·40	12·81	7·92	22·50
Sand	38·70	10·15	7·83	1·64	10·15
	100·00	100·00	100·00	100·00	100·00
Ammonia	9·34	13·90	9·77	8·64	9·76

In all those cases a very large depreciation in the value has taken place, and several of them are worth considerably less than half the price of the genuine guano, while they are generally offered for sale at about £1 under the usual price. The adulteration is chiefly practised in London, and cases occasionally occur which can be traced to Liverpool and other places; but it always takes place in the large towns, because it is only there that facilities exist for obtaining the necessary materials and carrying it out without exciting suspicion. The sophisticated article then passes into the hands of the small country dealers, to whom it is sold with the assurance that it is genuine, and analysis quite unnecessary. In other instances, adulterated and inferior guanos are sold by the analysis of a genuine sample, and sometimes an analysis is made to do duty for many successive cargos of a guano which, though all obtained from one deposit, may differ excessively in composition. In order to insure obtaining a genuine guano, it is above all things important to deal only with a person of established character, who will generally, for his own sake, satisfy himself that the article he vends is genuine and of good quality; and it is always important that the buyer should examine the analysis, and in all cases where there is the slightest doubt, should ascertain that the bulk sent corresponds with it. In the case of a Peruvian guano, a complete analysis is not necessary for this purpose; but an experienced chemist, by the application of a few tests, can readily ascertain whether the sample is genuine. Where the difference in value between different samples is required, a complete analysis is necessary, and this is indispensable in the case of the inferior guanos. Many of these are obtained from deposits of limited extent, and in loading it considerable quantities of the subjacent soil are taken up, so that very great differences may exist even in different parts of the same cargo. Nor must it be forgotten that, except in the case of Peruvian, the name is no guarantee for the quality of the guano, even if genuine. Peruvian guano is all obtained from the same deposits, those of the Chincha Islands, but the guanos which are brought into the market under the name of Patagonian, Chilian, etc., are obtained from a great variety of deposits scattered along the coasts of these countries, sometimes at a distance of several hundred miles from each other, and which have been accumulated under totally different circumstances. In illustration of this, it is only necessary to refer to the subjoined analysis of samples, all of which I believe to be genuine as imported, and which were sold under the name of Upper Peruvian Guano.

	I.	II.	III.
Water	7·80	6·65	8·85
Organic matter and ammoniacal salts	10·85	19·16	10·20
Phosphates	67·00	20·41	17·10
Carbonate of lime	...	21·15	...
Alkaline salts	11·10	5·31	61·30
Sand	3·25	27·32	2·55
	———	———	———
	100·00	100·00	100·00
Ammonia	2·29	5·73	1·48
Phosphoric acid in the alkaline salts	2·24	...	1·70
Equal to phosphate of lime	4·89	...	3·70

With the exception of Peruvian, the supply of good guanos of uniform composition is by no means large, and phosphatic guanos of good quality are now especially rare. The Saldanha Bay, and other similar deposits, have been exhausted, and few guanos of equally good quality have been lately discovered. There is no doubt, however, that such guanos are very useful, and if obtained in large quantity, and of uniform composition, would be used to a much larger extent than they at present are.