The discovery of a synthetic tannin, in 1911, by Dr. Stiasny, who was then an assistant in the Leather Industries Department of Leeds University, created a great deal of interest in the leather trade, and can certainly be regarded as a triumph of the application of chemistry to industry. It was thought at first that these tannins might play as important a part in the leather trade as the synthetic dye-stuffs have, but it is now generally believed that this will not be the case. Their use is likely to be as an aid to tanning, rather than as a complete tanning agent, although it has been found practicable to use them for one or two classes of light skins, where it is essential that the colour of the leather should be nearly white. The original patent was taken out in September, 1911, in Austria, the native country of the inventor, but the patent rights have also been protected in other countries, while the manufacture and sale of the product passed into the hands of a large German dye firm, who have since taken out several patents for other synthetic tannins. The original tannin is produced by treating a sulphonated phenol with formaldehyde. A patent had been taken out several years before for the use of formaldehyde in tanning, but this expired early in 1911; many patents had also been granted for sulphonated phenol preparations, chiefly as disinfectants, but it was left to Dr. Stiasny to discover the value of combining the two chemicals by the process of condensation. The preparation, first known as "neradol," is now made in England under licence, but, since the war, its cost has been more than doubled, so that it is unlikely to replace natural tanning materials to any great extent. Formaldehyde itself has certain properties which are harmful to leather, and it must be used with extreme caution and in small quantities to avoid these defects. It is used in the leather trade chiefly for keeping up the substance of hides during the tanning process, and thus causing a rapid absorption of tannin. At the beginning of the tanning process, the liquors are acidified, preferably with a weak organic acid, which causes the fibres of the hides to distend. It is at this stage that the formaldehyde is used. This method, which cannot improve, but may easily damage, the leather, is almost entirely confined to the Continent. Formaldehyde has a hardening and tanning effect on animal tissues, and leather treated by this process often has inferior wearing qualities. In the case of the artificial tannin, this property of formaldehyde is to a large extent modified by the chemical reaction with a sulphonated phenol, the addition of which also increases its tanning effect; but, while the tannage is very rapid, especially in the case of light skins, leather produced solely by means of artificial tannin has a slight tendency to dryness after being in stock for some time.