Sumach often contains much sand, and sometimes particles of magnetic iron ore, which cause black stains, and may be collected by a magnet, and which dissolve in dilute hydrochloric acid without evolution of hydrogen, to a yellow solution. Metallic iron, which is also attracted by the magnet, dissolves in hydrochloric acid with effervescence to a colourless or green solution. Good sumach contains at least 25-27 per cent. of tannin. The Author has analysed samples of undoubted genuineness containing as much as 32 per cent. of a tannin, principally gallotannic, with some ellagitannic acid, and a colouring matter (myricetin) identical with that of _Myrica nagi_ (p. 250), which gives yellows with alumina and tin mordants, and is fugitive to light. Sumach is the best tanning material known for pale colour and soft tannage, and is hence used for moroccos, roans, skivers, etc., and also for brightening leathers of darker tannages, such as mimosa, gambier, the colouring matters of which warm sumach liquors seem able to dissolve. In the report of the Society of Arts Committee on bookbinding leathers,[141] it is stated on abundant evidence, that sumach-tanned leathers are less affected by light and gas-fumes, and less liable to decay than those of any other known tannage. [141] Soc. Arts. Journ., 1901, p. 14. Sumach is frequently adulterated with the ground leaves and twigs of _Pistacia lentiscus_ (“schinia” or “skens”), _Coriaria myrtifolia_ (“stinco”), _Tamarix africana_ (“brusca”), _Ailantus glandulosa_, _Vitis vinifera_ (leaf of the common grape vine) and some other species of the Rhus family, but _Pistacia lentiscus_ is used to a much larger extent than any of the others. _Pistacia_, _coriaria_, and _tamarix_ all contain considerable quantities of tannin, though less than genuine sumach, and of a different chemical constitution. The most satisfactory method of detecting these adulterants is by microscopic examination, none of the chemical methods proposed being very satisfactory; though, as many of the added matters contain catechol tannins, while those of sumach are purely pyrogallol derivatives, the method proposed by Hughes for the detection of quebracho in oakwood by the reaction of concentrated sulphuric acid (p. 296) might render good service, and any sumach infusion which was rendered turbid by bromine-water would at least be open to grave suspicion. [Illustration: PLATE III. _Ailantus glandulosa._ _Coriaria myrtifolia._ _Colpoon compressa._ _Rhus cotinus._] [Illustration: PLATE IV. _Pistacia lentiscus._ _Rhus metopium._ _Rhus coriaria._ _Tamarix Africana._]