ANALYTICAL EDITION
November 15, 1942
obtained by independent analysts, one of whom used the A. 0. A. C. and the other the suggested method, indicates the reliability and accuracy of the proposed procedure. The average deviation from the official method for the 33 materials, other than the samples of soil, was 0.09 per cent. The average digestion time for materials other than soils by the perchloric acid method was 30 to 35 minutes, whereas that for the official method was between 1 and 3 hours. For soils, the digestion time by the rapid method was 35 minutes, in comparison with 2 hours by the official procedure.
Discussion The volume of perchloric acid that can be used without losing nitrogen is a direct function of the organic matter which remains after the preliminary sulfuric acid digestion. For this reason, an alternate method can be employed in which the use of sodium sulfate is not involved. Heat the sample with 25 ml. of cdncentrated sulfuric acid and I ml. of the selenium oxychloride solution for 25 minutes. Allow the digest t o cool, add 1 ml. of 35 per cent perchloric acid, and heat the mixture over a small flame until it is clear, as described
above.
This variation of the procedure is as accurate as the previously described method. The elapsed time for the complete digestion, however, is between 40 and 45 minutes. I n the absence of an organic substrate with which to react perchloric acid will oxidize the ammonia, with resulting loss of nitrogen. This explains why sodium sulfate cannot be used in soil digestions. The amount of organic matter in soils is comparatively low and most of it is oxidized by the sulfuric acid when sodium sulfate is added to raise the boiling point of the digest. During the perchloric acid phase of the procedure the temperature of the digest must be kept below the boiling point. If the solution is made to boil the perchloric acid will react a t too rapid a rate, with a resulting loss of nitrogen. The addition of salicylic acid did not materially lengthen the period of digestion. An average period of 32 minutes was necessary for samples containing approximately 2 grams of salicylic acid, Evidently the carbon contained in the salicylic acid is largely oxidized during the preliminary sulfuric acid treatment and therefore does not lengthen the total digestion period. This also explains why 0.5 cc. of 35 per cent perchloric acid is sufficient in spite of the large amount of carbon added in the salicylic acid. The perchloric acid method is also suitable as a wet-ashing procedure for the determination of plant ash elements, such as phosphorus, potassium, and calcium. The alternate rather than the first mentioned proceduie is to be preferred for this purpose.
Summary A rapid Kjeldahl digestion procedure involving the use of 35 per cent perchloric acid is proposed. An alternate method eliminates the use of sodium sulfate, with only a small increase in the length of period of digestion. The average digestion time for 1-gram samples is approximately 30 minutes. KO explosive hazard, because of the perchloric acid used, is believed to be involved. The results check closely with the values determined by the official A 0. A. C. method. The cost of the determination is reduced by eliminating certain reagents employed in the A. 0. A. C. method, such as mercury and potassium sulfide. Literature Cited Gauduchon-Truchot, H., “Contribution A l’fitude de la MBthode de Kjeldahl”, 1936. Le Tourneur-Hugon and Chambionnat. Ann. fals., 29, 227-9 (1936).
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(3) Mears, B., and Hussey, R. E., J. IND. ENQ.CHEM.,13, 1054-6 (1921).
(4) Pepkowitz, L. P., and Shive, J. W., IND.ENQ.CHEM.,ANAL.ED., 14, 915 (1942). ( 5 ) Stubblefield, F. M., and DeTurk. E. E., Ibid., 12, 396-9 (1940). JOURNALSeries paper of the Kew Jersey Agricultural Experiment Station. Department of Soils. Rutgers University.
Pressure Wash Bottle for Volatile Solvents LOWELL W. CHARKEY AND D. V. ZANDER Colorado Experiment Station, Fort Collins, Colo.
M
UCH time and energy can be saved in many laboratory operations by attaching to the mouthpiece of the con-
ventional wash bottle (of the type with the third tube for the thumb) a long piece of light rubber tubing connected to a compressed air line or air pump. I n using this device, a slow current of air is turned on and allowed to flow through the wash bottle continuously during the period of use, the air escaping through the thumb-hole tube. Delivery of liquid from the wash bottle is obtained instantly and for any desired period of time down to a small fraction of a second by placing the thumb over the thumb hole, thus creating pressure inside the bottle. ‘ompressed \_
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Thumb hole
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hole i n r u b b e r t u b e (when t h u m b h d e , i s Stopped, Qir posses i n t o flusk h e r e , crratinq preb5ure,
-Small
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In case the device is used for volatile solvents such as ether, petroleum ether, alcohols, etc., evaporation and consequent loss of solvent which would take place by allowing a current of air to pass promiscuously through the bottle are easily prevented by incorporating into the design a small bypass, best described in the accompanying diagram. This device, the liquid flow from which is entirely under control of the thumb, is the most effective the authors have seen for delivering a small quantity of a liquid in a forcible stream exactly when and where it is wanted.
