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BACK NUMBERS AND VOLUMES E have FOR SALE a limited number of the EARLIER VOLUMES and Numbers WE of the CHEMICAL NEWS and are prepared to supply orders at the following rates, CARRIAGE EXTRA, (subject to the Volumes or Numbers being in stock at the date when the order is received) : PRICES FOR SINGLE VOLUMES Various numbers, parts of Vols. 117 and 118 (1918/19) are only on sale at 2s. 6d. each. THE GENERAL INDEX TO VOLS. 1 to 100 can still be purchased at £1 1s. Al communications should be addressed to the MANAGER, CHEMICAL NEWS THE CHEMICAL NEWS, VOL. CXXXI. No. 3409. MERTON HOUSE, SALISBURY SQUARE, LONDON, E.C.4. TELEPHONES: Administrative Central 6521 Printing Works, Hop 2404. CRITICAL STUDIES ON METHODS OF ANALYSIS. XVI.--ZINC. By LEON A. CONGDON, A. B. GUSS, AND F. A. WINTER. (Contribution from the Department of Chemistry, Syracuse University.) INTRODUCTION. (Continued from Page 84.) I. M. Kolthoff and J. C. Van Dijk (95) state that the KCN method for zinc is less satisfactory than Jamieson's (35) volumetric KHg(SCN), method which they state gives excellent results in absence of Cl, and SO,. Also they state that NO, does not interfere with Jamieson's process, and when the zinc concentration is above 0.01 normal the solution may be filtered immediately after adding the ÑH ̧SCN, HgCl2 reagent. When the solution is less than 0.01 normal, the solution should stand one day before filtering. The excess of the reagent in the filtrate, which they titrate back by the Volhard method, must not be less than 0.06 normal. other methods for the estimation of zinc may be mentioned Turbidimetric, Colorimetric, and Indirect Gasometric methods. Turbidimetric methods are generally used for approximating small amounts of zinc. V. Berkner (99) has worked out such a method in estimating the zinc content of some foodstuffs. H. L. Lourie (100) reports two methods for determining zinc in egg products. M. Bodansky (101) made a study of determining small quantities of zinc, especially the zinc content of microorganisms. A turbidimetric method was used, which was based upon previous recommendations of Beyer and of Berkner. A. Del Campo (107) determines zinc colourimetrically in accordance with the fact that zinc gives a blue colour by SPECIAL NOTICE. All MSS., Books for Review, Business Letters and Communications of every description should be sent to the offices as under, and not to any other address. CHEMICAL NEWS, MERTON HOUSE, SALISBURY SQUARE, LONDON, E.C.4. resorcinol in alkaline solution. The character of the colour is altered somewhat on exposure to the air. The addition of HCl turns the solution red and this colour is not altered. Other metals do not interfere unless they have a coloured solution before the addition of the reagent-and if such is the case, the interfering metal must be removed. The sample suitable for test must contain 0.003 and 0.000005 gram of zinc. The standard used is a solution of 0.1 gram of pure zinc in HNO, and dilution to one litre. An aliquot suitable for comparison is taken and treated the same as the sample. The duplication method is used for comparison and should contain 70 cc. of H2O. The test in alkaline solution which gives the blue colour should be checked by the test in acid solution which gives a red colour. Edgar Beyer (102) devises an apparatus for the evaluation of zinc dust by the indirect gasometric method. The apparatus consists of a gas burette, a levelling bottle, and a generating flask. The burette has a 300 cc. bulb at the top and graduations from 300 cc. to 375 cc. The zero point coincides with the boring of a glass stop-cock above the bulb. The metal is dissolved in a fiask and the escaping gae, i.e., H., passes through a cooling spiral as described by de Koneck (103). L. A. Wilson (104) describes a gasometric method for the evaluation of zinc dust wherein he simplified the calculation involved by modification of the apparatus generally used. A factor is introduced to the fact that the vapour pressure over 10% H2SO, is lower than pure water. T. K. Rose (105) has revived an old method for the determination of zinc in coinage bronze, which was supposed to have been discredited half a century ago. It has been used at the Royal Mint and shown to be as accurate as other available processes. The method consists in volatil |