The nitrogen in these analyses is calculated as ammonia for the pffrpose of compari son. In reality, it exists in various forms of combination—viz., as uric acid, urea occasionally, orate. oxalate, hrdrochlorate, phosphate, etc.. of ammonia, other orates, guanine (q.v.), and undefined nitrogenous compounds. Bence, as may he inferred, a complete analysis of guano is a work of very considerable labor; but as its agricultural value depends mainly on the quantities of ammonia, soluble and iusoluble phosphates, and alkaline salts, which it contains, such analyses as those we have given are sufficient for practical purposes, and they are easily made.
As good Peruvian guano sold long at from £11 to £13, and latterly at about £14 per ton, there was a strong inducement to adulterate it. 'Umber, powdered stones, various earths, partially decomposed sawdust, and other substances, were used for tnis purpose, and specimens have been sold containing mere traces of the genuine article. Ilence it is expedient that large purchasers should either send a sample to a good chemist for analysis, or should cork up or retain a small quantity in a bottle for analysis, provided the crops to which he has applied his guano do not answer reasonable expectation. A chemist is attached to most agricultural societies and clubs, who performs such analyses for a moderate fee. The numerous analyses of prof. Anderson, late chemist to the high land society, and of other chemists, have had a very material effect in checking the sale of adulterated guano in Scotland, Still, the adulteration of manure, has for some time been rather more common in Scotland than in England. True, guano is not so often adulterated as some other fertilizers; but in England, the rigorous measures adopted by Dr. Voelcker and the royal agricultural society to expose dealers in spurious articles, and to suppress such traffic, have had a very beneficial effect. In Scotland, the agri cultural public awakened to the magnitude of the question. Several district :Ma Vilest' associations have been formed throughout the country. With all this machinery in full play, the fraudulent dealer will fortunately find his avocation as stiff work in Scotland as he has latterly discovered it in England.
Such facilities for analysis will to a considerable extent supersede the following ancient yet simple modes of testing the quality of guano. A pretty good idea, how ever, can be formed of the superiority or otherwise of the samples of guano by these tests: 1. Test by the guano, as is generally the case with the Peruvian mid
Chili varieties, is a uniform powder, weigh out two ounces, spread it on paper, and let it lie for two days in a dry and moderately warm room. What it may then have lost in weight must be esteemed superfluous water. .Many sorts of guano are so moist as to lose 20 or 25 per cent of their weight by this gentle drying. If we wish to deter mine the water with greater accuracy, a smaller quantity of guano should be placed in a shallow platinum capsule, and moistened with a few drops of hydrochloric acid. A heat of 212° may then be applied without loss of ammonia.
2. Test by half an ounce of the guano into an iron ladle, such as is used for casting bullets, and place it upon red-hot coals, until nothing but a white or grayish ash is left, which must be weighed after cooling. The best sorts of Peruvian guano do not yield more than 30 or 33 per cent of ash, while inferior varieties, such as Patagonian, Chili, and African guano, leave a residue of 60, or even 80 per cent; and those which are intentionally adulterated, may leave a still larger residue. Genuine guano of all kinds yields a white or gray ash; and a yellow or reddish ash indicates the adulteration with earthy matter, sand, etc.
This test is based upon the fact, that the most important ingredients, viz.. the nitro genous compounds, become volatilized, and escape, when subjected to a sufficient amount of heat. The difference of odor of the vapors evolved in the process, according as we are working with first or third rate guano, must also be noticed. The vapors from the better kinds have a pungent smell like spirits of hartshorn, with a peculiar piquancy somewhat resembling that of rich old decayed cheese; while those rising from inferior varieties smell like singed horn-shavings or hair.
3. The lime test affords a ready means of roughly determining the relative quantities of ammonia in different specimens of guano. Put a teaspoonful of each kind of guano. and an equal quantity of slaked lime, into a wine glass; then add two or three teaspoon fuls of water, and mix the substances together with a glass rod. Lime being a stronger base than ammonia, liberates the. latter from the ammonia salts contained in the guano: and the better the guano is, the stronger will be the pungent ammoniacal odor which escapes from the mixture. The slaked lime should be preserved in a dry and well corked bottle, so as to exclude the air.