Differences obtained in the estimation of nitrogen in the above substances are frequently the source of much annoyance. The cause of these discrepancies is chiefly due to the lack of uniformity in the material, and from its not being in a sufficiently fine state during the combustion. The hair which is found in commerce for the manufacture of fertilizers, is generally mixed with sand and dust. Wool dust often contains old buttons, pieces of wood, shoe pegs, and all sorts of things. The flesh fertilizers are composed of light particles of flesh mixed with the heavier bone dust. Even after taking all possible precautions to finely comminute these substances by mechanical means, still only imperfect results are obtained, for the impurities, that is to say, the sand, can never be so intimately mixed with the lighter particles that a sample of 0.5 to 0.8 gramme, such as is used in the determination of nitrogen, will correspond to the correct average contents. In substances such as dried blood, pulverization is very tedious.

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