Page:Timber and Timber Trees, Native and Foreign.djvu/87

 CHAPTER XI.

ON THE FELLING OF OAK IN SPRING AND WINTER.

bark of the Oak tree contains a substance called tannin, which is of considerable value, and is used in the preparation of leather. Therefore, in order to secure this tannin in its greatest quantity, it is the practice to fell, or cut down, the trees in the spring of the year, when the sap is rising. Under other circumstances, the trees would have been cut in the winter, while the sap was down and in a quiescent state—a period which has been almost universally recognised as the best for felling, as it is considered to ensure a better quality, and to be conducive to the greater durability of the timber. The value of the bark, however, generally overrides this consideration, since, although the weight in proportion to the contents of the timber will vary according to circumstances of growth, it is always thought profitable to save it, and, viewed under the commercial aspect, it is not likely to be disregarded.

The quantity of tannin contained in the bark of the Oak, as ascertained by Sir Humphry Davy, varies as follows, viz.: In Coppice Oak it is 32; middle sized, 29 and Oak cut in the autumn, 21 per cent.

The timber and bark merchants variously estimate the quantity of bark to the contents of the timber; and no doubt there is a very considerable difference in the