- The refuse bark from the tanner's yard is employed by the gardener as a source of heat, and when thoroughly broken down by putrefaction, as a manure.

As a source of heat, it is much less used than formerly, flues, steam, and the hot water system having very generally and most deservedly superseded it. Bark for heating requires frequent stirring and renewing, and if too much moisture be added, is apt to give out an excessive and irregular heat. In addition, it is a troublesome harbour for predatory insects.

Bark fresh from the tan-yard being thrown lightly together under a shed, must be gently moistened if dry, and turned over twice a week, to expose all its particles to the air. Unless this be done, the fermentation will not be general or regular. This is to be continued for a month or five weeks, in warm weather the shorter time being requisite, and then, having acquired a general and equal heat, it is ready for use in the stove. Usually it will continue to afford heat for a period varying between three and six months, but sometimes ceases to ferment without any apparent cause. Whenever the heat declines, the tan must be taken out, sifted, the dusty parts removed, and some fresh tan added. Sometimes turning the old tan and moistening it will be sufficient.

It is desirable, on the first formation of a bed, to mix new and old tan together, in which case the quantity of new bark to be brought into the pit will depend upon the goodness of the bark, and the bottom heat required. As much new tan as will fill two third parts of the bark-pit, with a mixture of old rotten, reduced almost to earth, will produce a bottom heat of about 85°; when old tan with higher remains of strength is used to modify the new, the same heat may be produced if the quantity be not more than half the capacity of the pit. This refers to a new pit; alter a bark bed has been in action, partial renewals of bark to keep up the heat are frequently sufficient in the reduced proportion of one-third, one-sixth, one-twelfth, or less. At intermediate stages between the partial renewals, the bed requires only to be excited to a brisker fermentation by forking up. About five-sevenths of the pit from the bottom should be occupied by the new and old tan as a fermenting body; and about two-sevenths from the top, or a little more than the depth of the pot, whatever that may be, should consist of old tan incapable of heating, so as to burn the roots of the plants; as least such should be the ordinary distribution of the tan; but where peculiar circumstances require a speedy augmentation of heat without displacing the pots, and when fruit is to be swelled off in the last stage, the earthy tan at top may be taken away, and new tan substituted. - (Abercrombie).

As a manure. See vegetable matters.