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 } | 65.62 | 50.83 | 55.73 | 46.26 | 11.17 | 12.86 | | salts } | | | | | | | | 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 L3 per ton. Of course, this is an extreme case, but it is no uncommon occurrence to find a difference of L1 or even L2 per ton between the values of cargos of Peruvian guano, which are sold at the same price.