Numerous patents have been taken for processes of chrome tannage. The first practical method was described by Professor Knapp in 1858 (see p. 210), though he did not recognise its value. Some of the patents have a historical interest, though of no importance. Among these may be mentioned that of Cavallin, a Swedish apothecary, whose object was dyeing rather than tanning, but who treated raw hide with a solution of bichromate, which was afterwards reduced on the fibre by one of ferrous sulphate. The leather produced is dark reddish brown, and tender from the amount of basic ferric salt formed at the same time. Mr. J. W. Swan, well known in connection with photographic processes, and electric lighting, also patented a process of chrome tannage (as an addendum to a patent on carbon printing), in which the chromic acid first fixed in the pelt was reduced by “oxalic, or other suitable acid.” Although it is possible to produce leather within the lines of the patent, the strongly acid reaction of the reducing agent renders it unsuitable for practical use. The first chrome tanning process which made any show of practical success, was that patented in 1879 by Heinzerling, which was acquired in this country by the Eglinton Tanning Company, and also worked under their license for a short time by the Yorkshire Tanning Company at Leeds. Though the process was not commercially successful on any considerable scale, it possesses points of interest which make a brief description desirable. The hides or skins, after preparation in the usual way, were treated in a mixed solution of salt, alum (or aluminium sulphate), and potassium bichromate, but no systematic attempt was made to reduce the chromic acid to a tanning form, the product being, at first at least, merely an alum tannage, coloured, and perhaps somewhat hardened with chromic acid, though on keeping for a length of time, reduction gradually took place at the expense of the hide-fibre, and of the fats employed in currying, so that the leather internally became greyish-green, and really chrome-tanned. Specimens of the early products of the process, preserved in the museum of the Leather Industries Department at Leeds, have now all undergone this change, but are still tough and flexible, showing that the rapid tendering of the Heinzerling leather, which was one of the causes of its failure, must have been due to some error in manufacture, and was not inherent in the process. Interesting, historically, is the fact, that at an early stage in the life of the patent, a specimen of the leather was submitted to the late Professor Hummel, in order that he should suggest some means of overcoming the disagreeable yellow colour of the product. He reduced it with a bisulphite, and coloured it with an aniline dye, and a piece is still in the possession of the Yorkshire College, and in perfectly sound condition. If legal publication of this experiment could have been