ANALYTICAL EDITION
July 15, 1943
Literature Cited
The figure of about 40 micrograms per gram for the whole wheat sample seems to be the correct nicotinic acid content as determined on the extract prepared according to Brown el al. There is little doubt that this is much lower than the true value, which is about 64 micrograms per gram (Q),and that the discrepancy is attributahle to incomplete extraction. A similar difference is evident in the case of wheat bran, and is again probably due to the method of extraction used. The value of 34 micrograms per gram for the nicotinic acid content of wheat germ (3, 16) is probddy too low. Assay of a more extended series of wheat germ samples in this laboratory has shown that the germ contains approximately the same amount of nicotinic acid as does whole wheat.
(1) Andrew, J. S.,Boyd. H. M., and Gortner, W. A,, IND, ENC. CHEM., ANAL.ED.,14,40 (1941). (2) Bohonos, N., Hutchings, B. L., and Peterson, W. H., J . Baet., 41, *n
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(3) Brown. E. B.,Thomas, J. M., and Bina, A. F., Cereal C h m . , 20, 201 (1943). (4) Qreene, R. D., Black. Archie. and Howland, F. O., IND.END. CXEM..ANIT.. ED.. 15. 77 (1943). (5) Ishell. H..J . B i d . Chs& 144,567 (1842). (6) Ives, M., Elvehjem, C . A,. and Strong. F. M., unpublished work. 17) , . Kline. 0. ~ A,. ~ersnna.1 ~ ~ communication. ~ . ^ (8) Krehl. W. A.. and Strong. F. MI, unpuhlished work (9) Melnick. D., Cereal Chen., 19, 553, (1042) (10) Neal,A. L., and Strong, F. M.. in ~ T ~ S S . (11) Potter. V. R., and Elvehjem. C . A,, J . B i d . Cfiern., 114, 495 (1936). Snell. E. E., and Strong, F. M.,Enzymologiia, 6,186 (1939). Snell, E. E.,and Wright, L. D., J . Rid Cfim.. 139,675 (1941). Stokes, J. L.. and Martin, B. B.. Ibid., 147, 483 (1943). Strong, F. M.,and Carpenter, L. E., Im. ENG.Cnm.. AN.&. ED.,14,909(1942). Teply, L. J., Strong, F. X., and Elvehjem. C. A,, J . Nutrition. 24,167 (1942). ~~~
Summar Modifications in the basal medium proponea ny m e i i and Wright (13) for the microbiological determination of nicotinic acid have been described, as well as a different procedure for growing the necessary inoculum. These variations have resulted in nearly doubling the response of the bacteria to quantities of nicotinic acid in the range 0.04 to 0.3 microgram, and have produced a linear standard curve. The assay as carried out at present is characterized by a muoh higher degree of consistency and uniformity than were usually obtained with the method as originally published.
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PREBENTED before the Diviaiun of igrieultuai and Food Chemistry, Joint Program yn Vitamins, at the 105th Meeting of the AUERICANC ~ X I C A L Socr~nu,Detroit. Mioh. Published with the ~ p p r o ~ of a l the Direotor of the Wisconsin Agricultural Experiment Station. Snppmted by gisnt from General Mills. Inaorporsted, Minneapolis.
A Spot Plate for Drop Tests PHILdP W. WEST Coates Chsemieal Laboratory Louisiana State UIiiverrity, Baton Rouge, La.
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T PRESENT two cotnmon types of spot plates are in use. When a solublei colored reaction product is anticipated, a white spot plate ie used. If the reaction product anticipated is a precipitat e (other than black, blue, or dark red), a black spot plate is ordinarilv selected. During investigations of various drop r eactions it became apparent that a combination black and wllite soot d a t e would be of advantage, and a plate of the de:iign &own in Figure 1 was ordered. Such a plate is obtained h j7 olacinn a black daze on half of an ordinary three-depression white Got plate: The line of d e markation between the bl sck and the white should run exactly through the centers of the three depressions. The plate as shown is adlaptable for either colored solutions or precipitates. Its great advantage lies in the hands of the experienced analyst to wliom each intermediate precipitate and color is significant, re@ :ardless of the form of the final test product. By observing intermediate colors or precipitates possible interferences due to complex ion formation, competitive reactions, etc., can bt? anticipated ( 1 ) . A further use is suggested by the work of V Jest and Houtman (Z), who propose a test for orthophosphate which depends on the formation of a yellow precipitate, best seen over a black surface, which is 17inn "roeinitate. hv mnvmtina it differentiated from interft..-, I___. to a blue compound Nhich should be observed over a white ~
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surface. The combination spot plate has proved invaluable, both in research and in the routine application of drop reactions. Spot plates of this design can be obtained after the war from the Fisher Scientific Comuany, Pittsburgh, Peuna.
Literature Cited [I) West. P. W., J . C h m . Education, 18, 528-32 (1941). (2) West, P.W.. and Houtman, Thomas, I N D . E N G . CHEM.,ANAL.ED.. 14. 5974 (1942).
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