There is an important difference in the value of the European and American products. The proportion of tannic acid in the latter exceeds that found in the former by 6-8 per cent., yet the former is much preferred by tanners and dyers. By using Sicilian sumach it is possible to make the finer white leathers, in great demand for gloves and fancy shoes; while by the employment of the American product, the leather has a disagreeable yellow or dark colour, apparently due to a colouring matter, which, according to Loewe, consists of quercitrin and quercetin, and exists in larger quantity in the American than in the Sicilian. The experimental results obtained by collecting sumach at different seasons were:-- Per Cent. of Tannic Acid. Virginia, mixed, collected in June, gave 22·75 " " " July, 27·38 " _R. glabra_ " August, " 23·56 " _B. copallina_ " " " 16·99 Sicilian, _B. Coriaria_ " " " 24·27 It is evident, therefore, that in order to secure the maximum amount of tannic acid, the sumach should be collected in July, but the colouring matter of the leaves has an important influence upon the value of the product. The leaves of the upper extremities of the stalks are always richer in tannic acid than those of the base; and the increase of age of the plant is accompanied by a general diminution of this acid. Yet the collection of the crop should be delayed as long as possible, because the diminution of tannin in the leaves will be abundantly compensated for by the quality of the product. Experiments upon the presence of colouring matters were made by treating gelatine solutions, and gave the following results:-- Virginia, mixed, collected in June, gave A nearly white precipitate. " " " July, " A decidedly yellowish-white precipitate. " _R. copallina_, " August " A dirty-yellow precipitate. " _B. glabra_, " " " A very dirty-white precipitate. Fredericksburg mixed, " " " A dirty-yellow precipitate. Sicilian " " " A slightly yellowish-white precipitate. It is therefore advised that for the purpose of tanning white and delicately-coloured leathers, the collection should be made in June; while for tanning dark-coloured leathers, and for dyeing and calico-printing in dark colours, where the slightly yellow colour will have no injurious effect, the collection be made in July. It appears that for all purposes, the sumach collected after the 1st of August is inferior in quality. [Illustration: Fig. 8.]