seem to have yet been tried. It is difficult to see why the alkali should always be used in so much greater excess than the oxidiser (in spite of inconvenient bumping), but it is especially strange that the distinguished author, ignoring Mallet's report of 1882, and republishing his directions without any revision, should leave the important question of time entirely out of account. Suffering persecution for the sake of the truth" should make the scientist keenly alive to any truthful criticism, and ready to study the contributions of his colleagues. The "ammonia process " has now passed from one laboratory into a hundred. If "discovered about a generation before chemists were prepared for it," the time is now fully ripe to collect the testimony of those who have used it; to agree upon the general conditions of quantity, rate of boiling, and limit of distillation, and even upon such details as the matter of paper or rubber connections. When a satisfactory compromise is effected we may hope to have a uniform method of procedure and a real definition of albuminoid ammonia. REPORT OF RECENT RESEARCHES AND IMPROVEMENTS IN ANALYTICAL PROCESSES. Zeitschr. f. angew DEXTRIN IN GENUINE HONEY. C. AMTHOR AND J. STERN. Chemie, No. 20, 1889.-44-9655 grms. of a sample of undoubtedly genuine honey were dissolved in 300 c.c. of water and allowed to ferment with yeast. After filtering and making up to 200 c.c., the liquid was examined in a Laurent's polariscope, and gave +24.9° in a 20 c.m. tube. The dextrin was then converted into dextrose, by heating 100 c.c. of the liquid with 10 c.c. of hydrochloric acid for three hours in a water-bath. After cooling and making up again to 100 c.c., the polarisation gave 9.21°, equal to 2 249 per cent. of dextrose. Allihn's gravimetric sugar process gave 2.266 per cent. The formation of dextrose points to the honey having contained dextrin. The authors further confirmed this view by preparing phenylglycosone. A large quantity of honey was fermented in a weak solution. The filtrate yielded on evaporation a brown thickish syrup, which was really an impure dextrin. After dissolving in a little water, phosphotungstic acid, containing some sulphuric acid, was added, and the liquid filtered. The excess of the reagent was removed by means of baryta water, and this in turn removed by cautious addition of sulphuric acid. After concentrating a little, liquor plumbi was added, the liquid filtered, and the excess of lead removed by hydrogen sulphide. The filtrate was evaporated in the water-bath until it became a thin syrup, and 200 c.c. of 90 per cent. alcohol were added, which was sufficient to keep the dextrin in solution. After filtering and evaporating, the dextrin was obtained as a brown syrup, which was purified with animal charcoal, until it was finally got as a yellowish brittle amorphous mass. It is exceedingly soluble in water, very hygroscopic, soluble in spirits of wine, but insoluble in absolute alcohol or ether. The watery solution very slightly reduces Fehling's liquid. 5 grms. of this dextrin were dissolved in 200 c.c. of water, mixed with 20 c.c. of 20 per cent. sulphuric acid, and heated for three hours in water-bath. The liquid was neutralised with barium carbonate, filtered, and evaporated to a syrup, which was repeatedly exhausted with alcohol. After distilling off a brownish syrup was obtained, which was purified by animal charcoal. It crystallises in granules, reduces Fehling's strongly, and the authors succeeded in preparing phenylglycoson, by warming 1 grm. with 2 grms. of phenylhydrozin, 3 grms. of sodium acetate, and 20 c.c. of water. The crude product was recrystallised from alcohol and obtained in small yellow needles, fusing at 204° C. This removes all doubt about the original substance being dextrin, the presence of which in honey may perhaps be explained by the bees feeding, when they get the chance, on malt in breweries. L. DE. K. TREATMENT OF URANIUM RESIDUES. D. LAUBE. Zeitschr. f. angew Chemie, No. 20, 1889.-The liquids resulting from the precipitation of phospates with uranium salts are kept in a large vessel, and the supernatant fluid is occasionally drawn off. When a sufficiency of precipitate has collected, the whole is heated to boiling in an iron vessel, and common soda is added until the precipitate seems dissolved. After cooling, and without filtering, ammonia is added until the mixture smells perceptibly of it, and the phosphoric acid is then thrown down with magnesia mixture, prepared by dissolving equal quantities of magnesium and ammonium sulphates. After, say, twelve hours, the liquid is syphoned off, and the residue washed with ammoniacal water. The united filtrates are now neutralised, either with hydrochloric or sulphuric acids, and freed from carbonic acid by boiling. The uranium is now precipitated by ammonia, as uranic-ammonic oxide. This precipitate is washed by decantation, but it is advisable to put a small quantity of ammonium sulphate to the wash water. By dissolving the precipitate in excess of nitric acid and evaporating, commercially pure uranic nitrate is obtained in crystals, which are allowed to drain on a funnel and washed with a very little cold water. L. DE K. 8 ESTIMATION OF TANNIC ACID IN OAK BARK, WITH PERmanganate. F. GANTTER. Zeitschr. f. angew Chemie, No. 20, 1889.-The author found that tannin is completely and quantitatively oxidised by permanganate when its solution is mixed with dilute sulphuric acid and boiled. To estimate the tannin in a sample of oak bark, the following solutions are wanted: 1. The usual bark decoction, 10 grms. per litre. 2. A solution of permanganate, containing 3.988 grms. of K, Mn, O, per litre. 3. A solution containing 7.951 grms. of oxalic acid per litre. 10 c.c. of the bark solution are mixed with 10 c.c. of dilute sulphuric acid, and heated to nearly boiling. Permanganate is now added, about 1 c.c. at the time, until the red colour but slowly disappears. The liquid is now once more heated to boiling, and permanganate is gradually added in excess, which causes a heavy brown precipitate. Oxalic acid is now run in until the liquid has become quite clear, and permanganate is then again added until red colour is restored. The total number of c.c.'s of permanganate used, less those of oxalic acid, is the amount reduced by the tannin, and at once represents the percentage of tannin in the sample. It is of course advisable to repeat experiment after removal of tannin by hide powder as usual. The author is now engaged in trying to find out the exact relation between permanganate and the other kinds of tannic acid. L. DE K. CORRESPONDENCE. [The Editor is not in any way responsible for opinions expressed by his correspondents.] To the Editor of the ANALYST. MILK ANALYSIS. DEAR SIR,-In an article on "Milk Analysis" in the ANALYST of November, 1889, Dr. B. F. Davenport states that the fat can be entirely extracted from the dried residue of 5 grms. of milk, if only this be in a flat-bottomed platinum dish of 24 inches diameter. He uses four separate quantities of boiling benzoline. Unluckily, he gives no comparative analyses to show that the fat is entirely extracted. For years I used exactly the method described, sometimes with larger flat-bottomed dishes, and always with more numerous changes of benzoline, boiled on the residue. The fat, however, was never entirely separated, nor even to within "one tenth of a per cent." In a paper in the February number of the ANALYST, 1889, he will see this method contrasted with more modern methods. In my experience, there are only four methods that extract all the fat from a milk. 1st. Soxhlet's Areometric method. 2nd. Soxhlet's tube with pumice, plaster of Paris, kieslguhr, or paper-coil (Adams). 3rd. The Lactocrite. 4th. The Schmid method; this last was described in the Chemical News, of November 1st, 1889. Yours faithfully, Analytical Laboratory, Vestry Hall, Harrow Road, ALF. W. STOKES, F.C.S. F.I.C. November 4th, 1889. To the Editor of the ANALYST. SIB, I have read with extreme interest, Dr. Bennett F. Davenport's article upon Milk Analysis, as printed in your last issue. I thoroughly agree with him in all that he has written concerning the estimation of the fat in milk, the process employed, being termed by him a modified Wanklyn. I am in the habit of using platinum basins of 24 inch diameter, but having quite flat bottoms, and have no difficulty whatever in obtaining a very thin and evenly distributed skin of residue, the complete extraction of which by means of petroleum ether, is easily accomplished. Petroleum ether as mentioned by Dr. Davenport, having a great advantage over that of ether in not dissolving either lactic acid or lactose. The process known as the "Adams blotting paper," and recommended by the Milk Committee of the Society of Public Analysts, is a process which I consider to be faulty, and that in three respects, and my reasons for saying so, are as follows: 1st. You cannot estimate directly both the fat and the solids not fat. 2nd. That the amount of fat obtained is in excess of that originally present in the milk, owing to an increase in weight, due to rapid oxidation of the fat when in contact with cellulose, when spread over such a large surface, and also to a further oxidation which takes place when completing the drying of the extracted fat in the water oven. 3rd. It cannot be used when the milk is not fresh, objections which are, in my opinion, fatal to any milk process. I used blotting paper in milk analysis in 1882 and relinquished its use owing to the last objection, and finally by a long series of experiments, satisfied myself as to the correctness of my second objection, and when coupling that with the first and the third objection, I have now no hesitation in rejecting it as faulty. My opponents may say that the fat calculated from the sp. gr. and total solids, agree with that found by Mr. Adams' process, but to that I reply, we have already had examples of altering formula to suit the particular process employed. I am, yours truly, WILLIAM JOHNSTONE. City Central Laboratory, 13, Fish Street Hill, E.C. November 4th, 1889. APPOINTMENT. Mr. J. Falconer King, Analyst to the City of Edinburgh, has been appointed Public Analyst for the County of Haddington. ERRATUM. --On page 217, vol. xiv., line 2, after 1889, read and Jour. Soc. Chem. Industry, September 1889." A MONTHLY JOURNAL DEVOTED TO THE ADVANCEMENT OF THE ANALYSIS OF FOOD AND DRUGS, AND OF GENERAL ANALYTICAL AND MICROSCOPICAL RESEARCH. EDITED BY JOHN MUTER, M.A., Ph.D., F.R.S.E., F.L.C., F.C.S., ETC., Late President of the Society of Public Analysts; Author of “ A Short Manual of Analytical Chemistry ; and of Text-Books on Pharmaceutical Chemistry and Materia Medica; Public Analyst for Lambeth, Wandsworth, Southwark, Rotherhithe, Newington, VOL. XV. 1890. LONDON: PUBLISHED FOR THE PROPRIETOR, BY MESSRS. BAILLIERE, TINDALL & COX, KING WILLIAM STREET, STRAND, W.C |