CXXVII., 289 (May 11), in which the author surveyed this comparatively unexplored field of research. The importance of a study of these phenomena is not confined to the research laboratory. Tanning processes are of a very similar nature, and the same applies to the treatments given to exposed photographic plates, films and papers to yield finished pictures.

It may also be suggested that geology would benefit by a deeper knowledge of these phenomena.

That Dr. Liesegang himself has utilised his results in this field may be inferred from his numerous studies in the chemistry of photography. J.G.F.D.

Laboratory Experiments in Chemistry, by N. HENRY BLACK. Pp. IX. + 165. London: MacMillan & Co., Ltd., St. Martin's Street, W.C.2. 1923. 5s. net. This little volume is intended as a guide for demonstrators and others, and is to be used with Black and Conant's "Practical Chemistry."

The experiments selected only involve simple pieces of apparatus and inexpensive chemicals, yet the ground covered by the book is very wide and the way is paved for more advanced work in the various branches of applied chemistry. The book therefore commends itself more particularly to those teachers of chemistry in technical institutes.

Experiments designed to illustrate fundamental facts have been marked with an asterisk.

tity of zinc, forming a non-fused granular alloy which, after washing, is smelted for the metals. The sulphur and some zinc chloride liberated in the chlorination are received in a condenser, the sulphur condensing as a layer upon the surface of a strong solution of zinc chloride in the condenser, while the zinc chloride vapour condenses and dissolves in the solution. From time to time zinc chloride solution is withdrawn from the condenser, mixed with fresh ore, and the mixture dried and fed to the chlorinating apparatus, and the solution in the condenser is made up with the wash water of the iron-lead alloy. The purified zinc chloride or zinc and lead chloride is electrolysed, and the chlorine is employed again for treating fresh ore The electrolysis is preferably effected in the apparatus described in Specifications 198024 and 208649, and the products successively deposited are, when nearly all the lead has been deposited, first impure zinc containing lead, copper, &c., and then pure zine, or, when the melt contains a substantial quantity of lead chloride first an alloy of lead, silver, &c., then pure lead, then a lead-zinc alloy, and finally pure zinc. The presence of some manganese during the electrolysis is advantageous, and a manganese compound may be added if manganese is not present in sufficient quantity. In a modification the chlorination is effected at a low temperature with sulphur chloride, as described in Specification 200,701, and the product (containing sulphur and sulphur chloride) is introduced into fused zinc chloride at 400-450° C., the mixture being treated with zine to precipitate the iron-lead alloy and the purified melt being then electrolysed, when chlorine and sulphur chloride are evolved; or the mixture of the chlorinated ore and zinc chloride may be heated to 600-700° C., for instance, by feeding it into a previously obtained melt kept at that temperature, when sulphur is distilled off, leaving a chloride melt which is treated with zine and subsequently electrolysed as before.

Messrs. Rayner & Co. will obtain printed copies of the published specifications and abstract only, and forward on post free for the price of 1s. 6d. each.

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