6 THE ANALYST. NOTE ON THE DETECTION OF ALUM ‘IN FLOUR BY THE LOGWOOD TEST. BY W. C. YOUNG, F.C.8. Read before the Society of Public Analysts, ort 26th June, 1878. IT must be admitted that a distinctive test, such as the logwood, would possese great value if the reaction given by it could be strictly assured in all case8 where alum is present. At the present time, however, very few chemists hare any faith in it as a test for alum in flour, so often have they failed in obtaining any indication of its presence even when it has been purposely added.With bread the case is different, as I have never failed to get the desired reaction when trying it upon samples t o which alum has been added in the process of manufacture. At first sight it is difficult to see why the reaction is not obtained with alumnised flour; in the case of bread one would expect some interference by reason of the decomposition of the alum which undoubtedly takes place in the baking, but in flour the alum must remain unaltered.Various reasons have been given to account for this difficulty, of which I may mention, the use of old logwood chips (or such as had been exposed to the air) for making the tincture; and the use of a wrong proportion of carbonate of ammonium solution to tincture of logwood.I have had recently several samples of flour, which, upon analysis gave quantities of phosphate of alumina equal to alum, varying from 15 to 25 grains in 4-lbs.) and as I could not in any of them obtain an indication by the logwood test, I felt I could not safely, in the face of what has recently occured at Selby, certify that it was present ; a t the same time I confess that if that case had terminated differently I should have done so.In connection with the examination of these samples I mixed alum with flour in progressive quantities, and, except in a few cases, failed to get the reaction, and in these few the colour was in patches in the under portion of the mass, the surface colour being the dirty brown usually given after standing a time when alum is absent, 60 that it may well have been passed as pure. I then applied the test to powdered alum and found that the colour came very slowlF, and where a considerable amount of carbonate of ammonium bad been used, the deep claret colour had changed to brown in the upper part of the liquid, before anything like the blue appeared in the lower.This result clearly indicated a solution of the difficulty, as it ahowed that it was necessary to have the alum dissolved in water: before applying the test, and upon mixing the dour t o a thin paste with boiling water previous to adding the ammoniacal logwood tincture, a blueish grey colour is developed in a few minutes, whiqh is unmistakmble with so amall a quantity as 5 grains of alum to 4-lbs.of flour ; the colour stands well for seven days, whereas the ordinary colour obtained without alum will not last aa many hours. Treated in this way the test answers well, no matter what age the logwood tinctwe may be, or what the character of the chips from which it is made, always provided that the deep claret colour is produced in it on the addition of solution of carbonate Qf ammonium.It appears to me very probable that the varying results I hare hitherto obtained may be due to the circumstance of my having added more at one time than another ofTHE ANALYST. 7 carbonate of ammonia, thus rendering the solution of the alum in some cases more easy than in othefs. How far these few facts affect the value of the decision of the Inland Revenue chemists in the ‘‘ Selby ” flour case, of course I am unable to say, but should it appear that they applied the test before having made sure that the alum was dissolved, I make bold to assert that they would have obtained no indication even had there been twice as much alum present as was certified by Mr. Allen.