Inorganic analysis

 

作者:

 

期刊: Analyst  (RSC Available online 1899)
卷期: Volume 24, issue 1  

页码: 51-53

 

ISSN:0003-2654

 

年代: 1899

 

DOI:10.1039/AN8992400051

 

出版商: RSC

 

数据来源: RSC

 

摘要:

THE ANALYST. 51 INORGANIC ANALYSIS. Bacterial Detection of Arsenic. F. Abba. (CerttralbZ. Bakteriol., 1898, [2], iv., 806 ; through Chem. Zeit. Rep., 1898, 310.)-Gosio has already shown that when Penicillium brevicazde is cultivated in presence of arsenic a garlic-like odour is produced. The present author finds that this process is not only simpler than ohemical methods of detecting arsenic, but, after investigating fifty other substances, that it is quite characteristic. It is also more delicate, for a piece of Indian fur 1 square millimetre in area gave the reaction, whereas even 5 square centimetres did not show the Marsh test. The material to be examined is placed in sliced potato, sterilized at 115" for twenty minutes, inoculated with 0.5 C.C. of sterilized water containing spores of the P.brevicaule in suspension, and cultivated either at 37" or at ordinary temperatures. Fresh cultures of the penicilliurn need only be prepared once a year. 3'. H. L. Colorimetric Estimation of Iron in Water. (Chem, Zeit., 1898, xxii., 1086.)-Lunge's colorimetric process for determining traces of iron in aluminium sulphate is very suitable for the examination of water. Instead of matching the colour of the aqueous solutions as in the usual method, each is shaken up with a measured quantity of ether, and after the layers of ether have been adjusted to the game length, the colour comparison is made in these. If the water under examination contains much organic matter an error may be introduced ; in this case the samples must first be evaporated in platinum, ignited, fused with sodium carbonate, and the melt dissobed in hydrochloric acid.A. Seyda. F. H. L. Remarks on the Determination of Zinc and Manganese as Sulphide. E. Murmann. (1CIonats7zefte fiir Chernie, xix., 404.)-On account of the difficulty of filtration, the determination of zinc or of manganese as sulphide is rarely resorted to, though the method is capable of yielding very accurate results. The author over- comes this drawback by adding mercuric chloride to the solution before precipitation. The precipitated mercuric sulphide enables the finely divided zinc or manganese sulphide to be filtered off and washed without difficulty, whilst in the subsequent ignition of the precipitate the mercuric sulphide is completely expelled. The author has also devised a new form of crucible specially adapted for the ignition of such precipitates in ti current of hydrogen gas.Its construction is shown in the accompanying figure. The crucible a has a perforated bottom b, to which is aftached a tube c, which can be either straight or bent at right angles. ,4 perforated plate fits into the bottom, and between the perforated bottom and the perforated plate is a plug of asbestos as used in the Gooch crucible. The mouth of the crucible is covered by an ordinary crucible lid. The precipitate is filtered off and also dried and ignited in the crucible, whilst by means of the tube at the bottom a current of hydrogen can be passed through it during the ignition. The %T crucible can, of course, be used for other similar purposes.H. H. B.-S.52 THE ANALYST. Estimation of Manganese aa Phosphate. E. A. Gooch and M. Austin. (Zeits. anorg. Chem., 1898, x+iii., 339.)-In this process the metal is thrown down as trimanganese orthophosphate, the precipitate converted into ammonium manganese orthophosphate, and finally weighed as manganese pyrophosphate. Its accuracy, therefore, depends upon the rapidity and completeness with which the Mn,P,O, is changed into MnNH,PO,, and the degree of insolubility of the latter, which, a s Fresenius and Munroe have shown, is considerably affected by the presence of ammonium chloride. The present authors have investigated the method under various conditions, ultimately finding that a very large excess of ammonium chloride (200 molecules of NH,C1 to 1 of MnNH,PO, in 100 or 200 c;c.of liquid) is absolutely indispensable to a quantitative conversion of the original precipitate into the double phosphate, and, moreover, that MnNH,PO, is not appreciably dissolved by ammonium chloride solution, provided excess of the soluble phosphate employed as a precipitant is always present. Details for the successful operation of the process are as follows : The original faintly acid liquid (containing. not more than 0-2 gramme of metallic manganese) is mixed either in a platinum or a glass vessel with 20 grammes of solid ammonium- chloride, 5 or 10 C.C. of a cold-saturated solution of microcosmic salt, and diluted to 200 C.C. ; dilute ammonia is then added in the cold drop by drop until it forms a slight excess. The whole is heated till the precipitate becomes crystalline, aIlowed to cool for half an hour, filtered quickly through a Gooch crucible with the aid of a pump, and washed (preferably) with very weak ammonia.The filtrate is always quite free from manganese, and if the precipitate retains traces of ammonium chloride, this can only lead to the formation of equally minute quantities of manganese chloride. It is better to arrange for a precipitate weighing about 0-4 gramme ; but even with smaller amounts the final error will average not more than 1 mgm. of manganese. I?. H. L. The Determination of Chromium Oxide in Algerian Phosphates. G. Schiiler. (Zeits. angew. Chem., 1898, 1101-1103.)-With the exception of Shephards chromium phosphate (Cr,P,O,) chromium has hitherto only been found in traces in phosphates, and never, to the author’s knowledge, in calcium phosphates.In Algerian phosphates, however, which have recently become of considerable irn- portance in commerce, chromium appears to be a constant though small constituent. For the quantitative estimation of the chromium the author employs B m o d i b - tion of J. Clarke’s method of oxidation with sodium peroxide (Journ. Chenz, $oc., lxiii., 1079). Ten grammes of the phosphate are dissolved in the usual mixture of hydrochloric and nitric acida, and the filtrate and washings evaporated to a pasty con- sistency, in order to expel the excesg of acid. The moist residue is taken up in as small g quantity as possible of hydrochloric acid, oxidized by boiling with sodium peroxide, and the residue again treated in the same manner.The united filtrates and waabiags (oolafaining the chromium as sodium chromate) are boiled down, and in order to con- phbely remove the excess of sodium peroxide are again strongly diluted and evaporated. The liquid is then acidified, and the chromic acid titrated in the usual mauner.THE ANALYST. 53 In this way the author found 0.057 per cent. of chromic oxide in a large repre- sentative sample of Algerian phosphate. C. A. M. Volumetric Estimation of Molybdenum. F. A. Clooch and J. T. Worton. (Zeits. amrg. Clzem., 1898, xviii., 312.) -The iodometric method of estimabbg molybdenum outlingd by Friedheim and Euler (ANALYST, 1896, xxi., 25) suffers from tihe defect that the precautions taken to avoid the disturbing influence of atmospheric oxygen are by no means sufficient. To be fairly accurate, the prooess requires carrying out as follows : The amount of molybdate taken for analysis must not contain more than 0.3 gramme of MOO, ; the excess of potassium iodide over that decomposed by bha molybdate must not be greater than 0.5 gramme ; the liquid should consist of 20 G.C.of the stroageat hydrochloric acid and 20 C.C. of water; it must be boiled down till only 25 C.C. are left in the flask; and the distillation must be conducted in a current of carbon dioxide carefully freed from air. Even under these conditions an error, corresponding to some 0.3 milligramme of molybdenum trioxide, is intro- duced by the oxygen dissolved in the water and acid; to obtain the best results, therefore, these reagents should be boiled before use.As an alternative way of deterniining molybdenum, the moIybdate may be reduced to pentoxide by heating it with acid and an iodide in an Erlenmeyer flask lighkly dosed with a bulb-tube, boiling off the excess of iodine, making the liquid alkaline, and finally titrsting it with standard iodine solution. F. H. L. Note on Drown’s Method of Determining Silicon in Steel. G. Auchy. (Jour. Amer. Chem. Soc., 1898, xx., 547-549.)-There is some reason to believe that in determining the silicon in steel by Drown’s method some of it escapes dehydration owing to the fact that, as the sulphuric acid becomes more concentrated, part of the iron salts separate out and form a protecting envelope round the gelatinous silica. To obviate this the author suggests evaporating with aqua regia and sulphuric acid, instead of with nitric and sulphuric acids, the liquid being rapidly boiled down in a small porcelain dish on a very hot plate, with a, watch glass suspended over the basin by means of glass rods. In this way the iron salt is kept in solution until the very last moment, when it suddenly crystallizes out and fumes of sulphuric acid appear. If a second similar evaporation be made before filtering, it is hardly likely that any appreciable qumtity of die& will escape dehydration. A number of test andysee were made in this way with steeIs containing 0.25 per cent. of silicon, and not more than an additional 0.005 per cent. was obtained by the second evaporation. A steel which gave 0.122 per cent. with one evaporation gave 0.126 per cent. on repeating the malyais and evaporating twice before filtering. It is aleo stated that the evaporation proceeds quietly and without bumping or spurting, even at the moment of solidification and after, so that no attention is required. C. A. M.

 

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