INDUSTRIAL A S D ENGINEERING CHEMISTRY
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unsatisfactory, impurities which were present probably being responsible for the erratic results obtained.
Results Table I gives the results of a nuniber of analyses made as described. To some of the samples various additions were made as shown. While the results of analyses that failed because of improper control of conditions are not included, it is believed that the data in the table are representative. The method is capable of giving very good results when no interfering substances are present. The algebraic mean of the errors is 0.3 part in a thousand, indicating slightly high results. The average error without regard to sign was 1.2 parts in a thousand Sulfuric acid up to 5 grams and nitric acid up to 2.5 grams may be present, but larger quantities lead to high results. The quantities of salts permissible are less.
VOL. 10, NO. 7
Results obtained with samples containing 0.02 and 0.09 gram of zinc were as satisfactory as the remits with 0.04 to 0.05 gram.
Literature Cited (1) Churchill, H. \'., and Bridges, R. W., "Chemical Analysis of Aluminum," p . 36, New Kensington, Pa., Aluminum Research Laboratories, 1935. (2) Clayton, \V. J., and Vosburgh, W. C., J . Am. Chern. SOC.,59, 2415 (1937). (3) Cohn, Ber., 34, 3507 (1902). (4) Jamieson, G. S.,J . 4 m . Chem. SOC.,40, 1036 (1918). (5) Kolthoff, I. N., "Volumetric Analysis," 1-01. 11, p. 267, New York, John Wiley & Sons, 1929. (6) Lundell, G. E. F., and Bee, M. K . , Trans. Am. Inst. J l i n i n g M e t . Engrs., 8, 146 (1914). (7) Metler, V., and Vosburgh, W. C., J . - i m Clrem. Soc., 55, 2625 (1933). RECEIVED February 9 i i , 1938.
Moisture Determination CHARLES W. GRIFFITHS, R. M. Hollingshead Corporation, Camdcn, S . J
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F INTEREST to those who use the Dean-Stark method of moisture determination will be this simple supplementary apparatus. It assists in reading the volume of aqueous distillate and entirely eliminates the error due to parallax which is so prevalent in this determination. The experienced operator will appreciate the difficulty of obtaining an accurate reading by attempting to hold the trap level and taking a reading with the naked eye. I n instances where the material to be tested is of high moisture content and only a 10-gram sample can be used, a n error of 0.1 cc. in reading the meniscus will mean an error of 1.0 per cent in the ultimate result. The error in larger samples will of course be proportionately less, but i t is difficult if not impossible t o eliminate such a n error without some kind of a n aid to hold the trap in its intended position while reading, and something to aid the eye and keep the eye and meniscus in the same plane. The author has found the supplementary apparatus particularly valuable where the Dean-Stark method of
moisture determination has been adapted to high-moisture compounds. The base of the apparatus stands upon three legs. Two of these are of the adjusting-screw type, and are used in conjunction with the bubble level to facilitate the leveling of the base. From the base arises a support for holding the trap perpendicular. A small spring clamp at the bottom holds the trap rigid. The eyepiece is an ordinary meniscus reader (Arthur H. Thomas Co. 2501) to which is added a wooden spool, one end of which is beveled to rest snugly in the eyepiece and is tightly held by a short piece of Gooch rubber tubing. Through the exact center of the spool, which is about 35 mm. long and 30 to 35 mm. in diameter, a 3-mm. hole is bored.
It is advisable to add to the top layer of distillate a few cubic centimeters of a solution of a n oil-soluble dye. This will color only the top layer, further distinguishing the two layers of liquid. In practice i t is best to place the eyepiece below the junction of the liquid and raise it till the entire upper layer appears colored (by the oil-soluble dye). If the junction of the liquids should come a t the tapered part of the trap, the jaws of the eyepiece will obviously not hold it in a horizontal position. This difficulty is overcome by using a block of wood 90 X .55 X 24 mm., holding the 55-mm. end flat against the base with the 90-mm. end a g a i n s t t h e graduated portion of the trap. The part of the clamp outside the V-shaped jaws may be clamped against the block and the eyepiece raised or lowered until t h e p r o p e r l e v e l is reached. RECEIVEDM a r c h 16, 1938.
