142 NOTE ON THE DETERMINATION OF SULPHATES IN FLOUR NOTE ON THE DETERMINATION OF SULPHATES IN FLOUR. BY G. D. ELSDON, B.Sc., A.I.C. (Read at the Meeting, February 3, 1915.) OWING to the use of acid calcium phosphate in self-raising flour, the estimation of sulphates present in flour has become almost a necessity. It is well known that this estimation cannot be made in the ash (compare O’Sullivan, ANALYST, 1914, 39, 425, and Cripps and Wright, ibid., 429); and even when the flour is mixed with lime previous to ignition, the result obtained by the writer has been far from satisfactory.The following method has been used by him and others for some time, and has been found to be fairly satisfactory : Ten grms. of flour are added to 25 C.C. of concentrated hydrochloric acid contained in a 250 C.C.beaker. The beaker is then gently warmed on the water- bath for a few minutes, and the whole frequently shaken until all the flour has been attacked and the liquid is of a deep purple colour. The whole is finally heated on the hot water-bath for about an hour, the beaker not, however, coming in contact with the steam, but being placed on the metal covering.About 100 C.C. of water are added, and after standing a few minutes the liquid is filtered, the filter-paper being washed once with cold water. The filtrate is then heated to boiling, barium chloride solution added, and the resulting barium sulphate weighed. Many samples of plain and self-raising flour have been examined by this proceos. In the case of a plain flour containing 0.4 to 0.5 per cent.of ash, the average amount of barium sulphate obtained in the above manner is 3.5 mgrms.-corre- sponding to 0.021 per cent. of CaSO, or to 0°012 per cent. of SO,. This is somewhat higher than the figures quoted by Cripps and Wright. This may be accounted for either by the oxidation of some organic sulphur in the above process, or by the failure of 1 per cent.acetic acid to extract the whole of the sulphate. The difference is, however, not very serious, and of little consequence in comparison with ths much larger amount of sulphate found in The method has been tested on flours containing known amounts of sulphate- the sulphate being added both as calcium sulphate and as that contained in impure acid calcium phosphate. Quantities of calcium sulphate were added to 10 grms.of flour as below, and the total sulphate estimated. The amounts of calcium sulphate found are corrected for that present in the original flour. phosphatic ” self-raising flours. Calcium Sulphate added. 0*0060 omo120 0.0240 0*0300 Calcium Snlphate found. 0.0055 0 *0110 0,0235 0.0290 0.2 grm. of acid calcium phosphate containing 12.0 per cent.of calcium sulphate was added to 10 grms. of flour and intimately mixed. The total sulphate was then estimated and found to be 0.25 per cent. as calcium sulphate, the amount added being equal to 0.24 per cent.SOLUBLE CHLORIDES AND TOTAL CHLORINE IN SOME ENGLISH COKES 143 When determining the sulphate present in a phosphatic self-raising flour, or in a plain flour which has been 6 K improved,” it will be advisable to allow 0025 per cent. of oalcium sulphate as that due to the sulphate normally present in the flour, as this seems to be the maximum amount likely to be present, except in the case of very low-grade flours. A portion of this work was done in the Birmingham Municipal Laboratory, and I am much indebted to Mi. J. F. Liverseege both for suggestions and for permission to use that part of the work done in Birmingham. MUNICIPAL LABORATORY, REGENT ROAD, SALFORD.