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pyrophosphoric acids present. The alkali required to neutralize the acidity resulting from the formation of normal silver orthophosphate is used as a measure of the orthophosphoric acid content. From analyses on samples of liquid anhydrous phosphoric acids containing 74 to 85 per cent of phosphorus pentoxide an equilibrium constant is calculated for the reaction H4P207 = H3POI H P 0 3 .
+
Literature Cited (1) Allen, N., and Low, G. W.,IND.EKG.CHEM.,Anal. Ed., 5, 192 (1933). ( 2 ) Aoyama, S., J . Pharm. SOC.J a p a n , No. 520, 553 (192.5).
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(3) Britske, E. V., and Dragunow, S. S., J. Chem. Ind. (Moscow), 4, 49 (1927). (4) Dworzak, R., and Reich-Rohrwia, W.,Z. anal. Chem.. 77, 14 (1929). ( 5 ) Kiehl, S. J., and Coats, H. P., J . Am. Chem. Soc., 49, 2150 (1927). (6) Kolthoff, I. M., and Furman, N. H., “Volumetric Analysis,” Vol. I, p. 129, New York, John Wiley & Sons, 1925. (7) Lum, J. H., Malowan, J. E., and Durgin, C. B., Chem. & M e t . Eng., 44, 721 (1937). ( 8 ) Menzel, H., and Sieg, L , 2. Elektrochem., 38, 283 (1932). (9) Smith, G. F., and Sullivan, V. R., J . SOC.Chem. Ind., 56, 104T (1937). (10) Stollenwerk, IT., and BLurle, A., Z. a n d . Chem., 77, 81 (1929). (11) Travers, 9.,and Chu, Y . K., Helv. Chim. Acta, 16, 913 (1933). RECEIVED May 9, 1938.
Determination of Age of Inks by the
Chloride Method JOHS FINN, JR.,
AND
ROBERT E. CORNISH, 916 Kearny St., San Francisco, Calif.
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EVERA4Lyears ago the authors nere called to the defense of a young man accused of cheating on a state bar examination. It was claimed that he had made additions to his examination book several months subsequent to the examination date. The additions had been examined by a wellknown expert criminologist, mho had used the chloride method of Turkel (6) and had found the chloride migration in some of the suspected additions less than in other ink on the same page of the examination book. The young man was, therefore, threatened with being forever disbarred from the practice of lam.
FIGURE1. CHLORIDEMIGRATIONTESTS
The present authors observed that the alleged additions were made in a different color of ink from the body of the writing on the page under consideration. The question therefore arose as to whether the rate of chloride migration from all chloride-containing inks would be identical.
Rate of Chloride Migration Comparative tests were therefore made on various commercial inks, using the method previously reported (1). The document was immersed in a 2 per cent solution of silver nitrate, washed three times with distilled water. and developed with the photographic developer D72. This destroys the ink, but does not blacken the paper as permanganate does. The essential advantage of this process is its simplicity. It was found that the rate of chloride migration does depend on the nature of the ink. I n particular “Sanford’s Royal Blue” ink showed very little migration of chloride during the time allotted, while a maximum migration was shown with “Shaeffer’s Skrip Permanent Royal Blue.’’ These results seemed in principle to be a t variance u i t h tests made by one of the experts for the prosecution. This man, a chemist for a large ink manufacturer, testified that he had made up a number of inks containing methylene blue or methyl violet dye. To these inks he had added various amounts of hydrochloric acid (presumably forming hydrochlorides of the dyes) and of inorganic chlorides (of unspecified composition). When these inks were used for writing on a sheet of paper, the chemist observed no difference among the various inks in the rate of migration of the chloride away from the ink stroke. I n vien of this apparent discrepancy with results of the present authors, and since the case of the young man has not yet been finally adjudicated, it was decided to carry out further tests. Sanford’s Royal Blue ink was selected for these tests, since the previous sample had been shown to give a slow chloride migration. Yarious inorganic compounds were added to samples of this ink, as indicated in Figure 1, to determine whether chloride migration could be accelerated or retarded. The writing was done December 21, 1937. On January 26, 1938, the right-hand strip was cut off and the chloride metallics were developed as metallic silver. The center strip was cut off March 8, and developed in the same way.
SEPTEMBER 15. 1938
AKALYTICAL EDITIOK
It is evident that salt progressively migrates without evaporation. It was found t h a t the rate of chloride migration from the ink strokes was greatly increased by the addition of sodium chloride, and to a lesser extent by hydrochloric acid. The hydrochloric acid image appears, however, to fade rapidly, largely disappearing from the paper. Some of the results are shown in Figure 1, which speaks for itself. The third line from the bottom was written with an ink containing 0.5 per cent of sodium chloride, or about 0.30 per cent of added chloride. The image is much heavier than that in the eighth and ninth lines from the bottom, Tvhere the ink used contained 1 per cent of 12 S hydrochloric acid, or about 0.426 per cent of added chloride. It appears, therefore, that in the latter case the chloride must be dissipated by some process other than diffusion through the paper; evaporation of the hydrochloric acid seems the only possible explanation.
Effect of Added Chloride Experiments were also made to compare the effects of adding chlorides of sodium, calcium, zinc, copper, and tin. It x a s thought that the more deliquescent chlorides, such as calcium and zinc chlorides, might shoiv a more rapid chloride migration than sodium chloride Previous investigations had shown that the rate of chloride migration was very sensitire to moisture content-for example, samples of writing stored a few inches from a steam-heated radiator showed no detectable chloride migration even after six months. But as far as could be observed, the sodium, calcium, zinc, and cupric chlorides, when added to the ink, gave essentially the same rate of chloride migration. A totally unexpected result v a s found with stannous chloride, which seemed, when added to ink, to give practically no chloride migration froin the ink stroke; the extent of the migration was considerably less than with the untreated ink. The explanation may be as follows: Stannous chloride is
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probably rapidly oxidized to stannic compounds on the paper. There are only two added chloride atoms for each tin atom, so that a basic stannic chloride is probably formed. Such a substance may well bind the chloride firmly enough essentially to prevent its diffusion. But on addition of silver nitrate, silver chloride is probably formed, so that a silrer image is developed by the chloride test wherever there has been insoluble basic stannic chloride. An alternative explanation may be that the tin remains as nondiffusible, stannous compounds, which reduce silver nitrate directly and give a spurious “chloride” test. The paper was therefore carefully observed after immersion in the silver nitrate, hut before developing. S o blackening TT as seen at this stage, showing that the image frclm the stannous ink must have been a genuine chloride image; the silver had been firit precipitated as silver chloride and not as silver metal. It therefore appears that stannous chloride, added to the ink, definitely slom the rate of migration of the chloride in the paper.
Conclusion Since so many factors are concerned in the chloride test for age of inks, any conclusions regarding age of writing, as determined by this test, should be viewed with extreme suspicion. Inks used by federal offices and in banks should contain a definitely known amount of sodium chloride. This vould not only aid in readily identifying the ink, but would also make it possible to determine something of the time element.
Literature Cited (1) Cornish, R . E.,Finn, John, Jr., and hIcLaughlin, William, IND. ENQ.CHEY.,News Ed., 12, 315 (1934). (2) hlesger, O., Rall, H., and Hess, IT., Arch. H-~imind.,92, 108 (1933). R E C E I Y E D ‘ J U ~1, ~
1938.
Evaluation of the Vitamin A Potencv of Feeds G. S. FRAPS Texas Agricultural Experiment Station, A. & M. College of Texas, College Station, Texas
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HE most important values of commercial feeds are their productive energy, digestible protein, and bulk or volume. Fraps (4, 7 ) has shown that the prices of unmixed feeds are, in general, related to their productive energy and digestible protein; with bulky feeds, such as hays, bulk or volume also has a cost. Some feeds have additional values on account of special constituents. These include alfalfa meal and alfalfa-leaf meal on account of vitamin A potency, milk products on account of vitamin G, and bone meal on account of calcium and phosphorus. The fact that domestic animals under some conditions, do no receive enough vitamin A has recently been recognized. Growing chickens and laying hens are the most frequent sufferers in this respect (26, 27, 28). Milk coivs mag suffer from vitamin A deficiency --hen fed on low-grade roughage (6). Other animals may also receive insufficient vitamin A, when fed on restricted rations, as when the pastures have dried up. Even when fed sufficient quantities to maintain good production, hens may not receive enough vitamin A to produce eggs of high vitamin A potency and milk cows may not receive enough to produce milk or butter fat high in vitamin A potency (5, 27, 28).
Recognition of these deficiencies and desire to correct them have led to demands for information regarding the vitamin A potency of feeds, and methods for evaluating suitable carriers of vitamin A potency. Biological methods for estimating vitamin A potency, such as the Sherman-hlunsell method, the U. S. P. method, and the single-dose method, are expensive, require considerable time, and are not highly accurate. They are suitable for special purposes but not practical for the commercial evaluation of animal feeds.
’C-itaminA Potency Vitamin A potency may be due either t o vitamin A, a colorless substance, or to carotene or cryptoxanthin, yellow substances. Carotene seems to be changed to vitamin A by animals and stored as such, for the most part in the liver. Vitamin A as such is not present in animal feeds unless fish liver oils or their concentrates have been added, and when so added may be almost entirely destroyed in 4 weeks (6). The loss of added vitamin A has been studied by Fraps and Kemmerer through absorption of ultraviolet light at 328 mu as measured in a spectrograph ( 6 ) . This is not at present a practical method of evaluating the \-itamin A
