Abstract Published this Week. 232,898.-Aluminium Cements.-Patrouilleau, L. G., and Alumine et Derives, 2, Cite Monthiers, Paris. Cements, Portland, materials and compositions for.-A substance capable of furnishing sulphur dioxide is added to the raw materials for making aluminous cement to prevent the formation of silicates. The added substance may be hydrogen sulphide, sulphur, sulphides, hyposulphites, sulphites, sulphates, sulphur dioxide, sulphur troixide, or the product of dehydration of the acid H,SO,. It may be added before, during, or after charging the materials into the furnace, or if gaseous mixed with the blast. Examples are given illustrating the use of iron pyrites, ferrous sulphate, ferric sulphate, aluminium sulphate, and calcium sulphate. INTER B.Sc., requires Post for four weeks in July, in Chemical Works (London). -N.L., Chemical News. "THE CHEMICAL NEWS." 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DETERMINATION OF LEAD IN MINUTE QUANTITY IN BAKING POWDERS, LIME, ALUM, TARTRATES, CITRATES, AND CARBONATES IN THE PRESENCE OF IRON AND COPPER. By WILFRED W. SCOTT. Professor of Analytical Chemistry, Univerty Southern California, Los Angeles, California, U.S.A.) The method herein given is the result of an investigation in an effort to obtain a suitable method for determining minute quantities of lead in baking powders, alums, cream of tartar, and similar products in which traces of lead would be considered objectionable. Lead may be determined quantitatively in three general ways: (a) Gravimetrically in the form of an insoluble salt, as a sulphate, chromate, a sulphide, etc. a 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. (b) Electrolytically in the form of lead peroxide. (c) Colourimetrically in the form of a coloured salt. The first and third of these general methods are employed in the scheme of analysis. The conversion of lead to an insoluble salt that will dissolve in a special reagent from which it can be reprecipitated in a form readily seen in very dilute solutions, is the method in brief. The purpose of the first step is to eliminate elements that would give dark sulphides, the form in which lead is best seen in dilute soutions. Iron and copper are metals apt to occur with lead in the class of materials for which this method is desired. Bismuth, tin, cobalt, and nickel, fortunately, will be eliminated in the process. The sulphites of those undesirable metals are soluble, while lead sulphate is insoluble, a fact that makes it possible to remove lead. The following table gives the solubility of the elements in parts per 100 and shows why the sulphate of lead is the best form for the first step in the analysis. Chromate Phosphate Sulphide 0.00420 0.00002 Chloride 0.000014 0.00010 0.673 32,80000 20,00000 Insoluble The limits of delicacy of this method range from 0.01% to 0.0005% on a ten-gram sample, though, of course, this range could be increased on larger or smaller samples. than the upper limit were too dark for an accurate colour comparison. Lead sulphide precipitated with the concentration of 0.002 grams per fifty cc. of solution, although as low as 0.00001 gram lead per 50 cc. of solution, could be faintly seen in form of the sulphide, yet this was not sufficiently definite for accurate work. Phosphates of lead are practically insoluble in ammoniacal ammonium acetate. Fortunately, sulphuric acid decomposes those salts forming lead sulphate and the free phosphoric acids. |