when it may be used in larger quantities than in the case
of cereals. When applied to the turnip crop, it is well to use the more
phosphatic guanos or to supplement it with superphosphates. By applying
it in two lots, the larger portion before seed-time and the rest between
the drills after the turnips are up, excellent results have been
obtained. It has also proved an admirable manure for mangels. On the
whole, it gives best results on heavy soils and in a dampish climate.

_Adulteration of Guano._

Probably no artificial manure has been subjected to greater adulteration
in the past than guano. This has been due to the fact that the practice
of selling guano on analysis--especially among retail buyers--did not
largely obtain in the early years of the trade. A good deal of this
adulteration was probably caused by ignorant prejudice on the part of
the farmer, to whom the pungency of its smell and its colour were too
apt to be ranked as its most important properties. The variation in the
quality of different kinds of guano was too often not sufficiently
realised by the buyer, who not unfrequently was made to pay as high a
price for guano of an inferior quality as he ought to have paid for that
of the best quality. Indeed no manure illustrates the importance of
chemical analysis more than guano. Among the different forms of
adulteration practised may be mentioned the addition of such substances
as sawdust, rice-meal, chalk, sulphates of lime and magnesia, common
salt, sand, earth, peat, ashes of various kinds, and water. There can be
no doubt, however, that such adulteration has now long ceased to be
practised to any extent. Nevertheless, it may be of use to draw
attention to one or two of the tests by means of which some of the
commoner forms of adulteration may be detected. One or two are extremely
easily detected--as, for example, adulteration with sand or other
mineral substances. In such a case, the percentage of ash left on
burning a small portion of the guano will be found to be excessive. The
percentage of ash in a sample of genuine Peruvian guano should not
exceed from 50 to 60 per cent. The colour of the ash is another
important point, and may serve as a further indication of adulteration.
In the case of genuine guano, this should be whitish or greyish.
Red-coloured ash generally points to the adulteration of the guano with
some mineral substance containing iron--such, _e.g._, as Redonda
phosphate, a mineral p