INDUSTRIAL A N D ENGINEERING CHEMISTRY
406
Discussion
T.4BLE 11. RELATIVEINTENSITY O F PINK COLOR OBTAINED WITH BASICFUCHSIN AND CARBON (Reaction with 0 . 2 gram of Digestive Ferments c o . glucose dissolved in 1 ml. of reagent a t a room temperature of 2 4 O C.) Reagent No. 1 2 3 4
Fuchsin National Aniline and Chemical Co.. 89% dye content, certification No. N F 31
5
6 7
8 9 10
11 12
National Aniline and Chemical Co., 94% dye content, certification No. N F 29 Rlerck’s medicinal, control No. 30,287
1.O 1.0 1.O
Carbon Norit A Nuqhar Norit A Nuchar Eimer &Amend Darco S-51 Norit A Nuchar
3.4 3.4 1.0 1.0
Norit A Nuchar Norit A Nuchar
Grama ofSOt 1.3 1.3 1.0
1.0
l ~ $ ~ ~
Moderate Palest .Moderate Moderate h\loderate Moderate Light Light Strong Strongest
Reproducibility of Results I n order to demonstrate the reproducibility of the reagent, twelve different lots were prepared, employing different fuchsins and different decolorizing carbons. The results of tests upon pure glucose (Difco Laboratories, Inc., dextrose, Lot No. 316,282), given in Table 11, indicate that various combinations of carbon and fuchsin can be used successfully with but minor variations in the amount of color produced. They also indicate that an increase in the amount of sulfur dioxide tends to reduce the sensitivity of the reagent, although the carbon used may be a secondary factor in modifying the sensitivity.
35
c.
Schif€’s aldehyde reagent has seldom been used in testing carbohydrates for aldehydic groupings, although it has occasionally been employed to determine the presence of oxy~ cellulose y in cellulose (3, 4). Some standard textbooks even state that the reagent does not react with glucose or other simple aldoses (6, 7 , IO). This is probably due t o the fact that as ordinarily prepared the reagent is relatively insensitive. The more sensitive reagent here described should be useful in routine qualitative testing of carbohydrate unknowns in laboratory instruction, as well as in research. It may also be used in a striking lecture demonstration of the presence of free aldehydic groups in solutions of aldoses, by applying the test to glucose on a large scale, with sucrose as a control. KO originality is claimed for the use of carbon as a d e colorizing agent for reagents containing leuco basic fuchsin. It has been so used by other workers (2, 5 ) , but seems not to have attracted general attention. Inits present form, the test is satisfactory for simple aldoses, maltose being the only other common carbohydrate giving a strong enough pink color to interfere. The author hopes later to develop the method further to permit the detection of the very small amounts of free aldehyde in solutions of substituted aldoses in a more definite fashion. Some of the compounds recorded as giving a negative (colorless) reaction or a faint false positive test,in Table I, showed an appreciable pink color in the still undissolved solid shortly after addition of the reagent but lost this color when all the solid had dissolved.
Literature Cited
The Norit A was marketed by the Pfanstiehl Chemical Co. The Nuchar was sold by the Eastman Kodak Co., reagent No. 776. The Eimer and Amend carbon was an 8- to 14-mesh activated coconut charcoal. I t was used in an attempt to obtain more rapid filtration and reduce the time of exposure to the air, but the rapidity of gtration was not increased, and the amount of carbon had t o be raised to 7 grams to obtain a completely . . colorless reagent. Both samples of National Aniline and Chemical Co. basic fuchsin had been certified by the Commission on Standardization of Biological Stains, but nevertheless their solutions showed a considerable brown color after treatment with sulfur dioxide. A fuchsin which would not show this discoloration when reduced to the leuco condition in solution would permit the preparation of a very sensitive Schiff’s reagent without the necessity for carbon treatment. Many other varieties of basic fuchsin and carbon can undoubtedly be employed, although it may be necessary to make slight changes in the amount of sulfur dioxide and carbon. Commercial fuchsins not only vary somewhat in the chemical composition of the dye, but also vary from about 80 per cent to 95 per cent in true dye content as put on the market. Thereafter they frequently slowly deteriorate with age, with the formation of a brownish water-soluble material and a black water-insoluble material (9). Therefore each new lot of the reagent should be carefully standardized against glucose and sucrose. It is also a good plan to run a blank without any carbohydrate present. Any development of color in the blank, particularly a deeper pink in the topmost layer than in the deeper portions of the mixture, indicates that the sulfur dioxide content of the reagent is too low and that atmospheric oxygen or possibly evaporation is restoring the color of the fuchsin. When properly prepared, the reagent is extremely stable. The results in Tab!e I were obtained with a feagent prepared from the National Aniline and Chemical Co., basic fuchsin cytification No. P\’F29, 94 per cent. total dye content, and decolorized with Norit A iron-free decolorizing carbon (Pfanstiehl). It had been standing in a nearly full, colorless, glass-stoppered bottle for 13 months, extosed to diffuse daylight and laboratory temperatures of 20’ to
Vol. 14, No. 5
(1)
Cantor, S. M., and Peniston, Q. P., J. Am. Chem. Soc., 62, 2113
(1940). (2) Coleman, L. C., Stain Tech., 13, 123 (1938). (3) Do&, Charles, “Methods of Cellulose Chemistry”, p. 123, New York, D. Van Nostrand Co., 1933. (4) Flint, E. R., and Tollens, B., Ann., 272, 289 (1893). (5) Hediger, E. M., Chenoweth, M. B., and Gold, H., J. Am. M e d . Assoc., 114, 1424 (1940). (6) Holleman, A. F., “Textbook of Organic Chemistry”, 6th ed., p. 233, New York, John Wiley & Sons, 1925. (7) Huntress, E. H., and Mulliken, S. P., “Identification of Pure Organic Compounds, Order I”, p. 16, New York, John Wiley & Sons, 1941. (8) Tobie, W. C., Food Research, 3, 499 (1938). (9) Ibid., 6, 15 (1941). (10) Wertheim, E., “Textbook of Organic Chemistry”, p. 332, Philadelphia, P. Blakiston’s Son & Co., 1939.
Stable Sodium Thiosulfate and Starch Solutions JACOB EHRLICH 153 South Doheny Drive, Beverly Hills,Calif.
A
’
0.1 N sodium thiosulfate solution that will retain its original titer approximately 5 months is readily prepared by combining 0.05 per cent sodium hydroxide and 0.1 per cent sodium benzoate as preservatives. A stable starch solution, essentially the preparation of the Association of Official Agricultural Chemists, modified by the addition of sodium benzoate, has the composition: 0.6 per cent soluble starch, 0.1 per cent sodium hydroxide, 0.3 per cent potassium iodide, and 0.1 per cent sodium benzoate. I n an iodometric titration 1 cc. of this solution is sensitive in a volume of 200 cc.
