JULY 15, 1937
ANALYTICAL EDITION
chromium. It is possible in solutions of ordinary analytical strength (10 mg. of metal ion per ml.) to detect the ferric iron in the original solution, since aluminum, mercurous mercury, mercuric mercury, and manganese salts do not precipitate before the red color has appeared. The solution can be approximately 0.06 N in hydrochloric acid, 0.06 N in nitric acid, or 0.03N in sulfuric acid without affecting the sensitiveness of the test. However, if the sohtion is strongly acid, i t can be neutralized to the point of incipient precipitation with ammonium hydroxide or sodium hydroxide solution and then the test applied. Oxalates, tartrates, and citrates are not usually present in a solution which is to be examined qualitatively, but if they are present they interfere with the detection. From the very
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nature of the test, phosphates must be absent since they precipitat8ethe ferric iron. Sugar and glycerol have no effect upon the reaction. In short, the test compares favorably with the common methods which are employed for the detection of ferric iron. Above all, the compound is not difficult to prepare and is not costly.
Literature Cited (1) Neoki, M., and Sieber, N., J . prakt. Chem., (N. S.) 23, 147 (1880). (2) Nichols, M. L., and Cooper, S. R., J . Am. Chern. SOC.,47, 1268 (1925). (3) Wagner, A,, 2. anal. Chem.,20, 349 (1881). RECEIVED April 20, 1937.
A Sloping Manometer MILTON BURTON Department of Chemistry, New York University, New York, N. Y.
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EITHER the McLeod nor the Dubrovin gages are suitable for the measurement of pressures of the order of 1 mm. when the pressure is subject to constant variation and must be continuously followed. I n a previous article (1) reference was made to a sloping manometer used for rapid and accurate measurement of such pressures; because of its convenience, some curiosity has been expressed as to its design and the method of filling. The complete manometer, together with the filling equipment, is shown in Figure 1. Although the method of filling is fully as rapid as that of Doja @),there is an advantage in that the mercury is boiled out within the apparatus and that the mercury which passes into the manometer does not come into contact with stopcocks or the grease there present. The rapidity and convenience of thia method are an advantage over Cameron's distillation method (2). Ordinary boiling out is, of course, an unsatisfactory method of filling this type of manometer because of manipulative difficulty and because even a trace of residual gas becomes an important factor in sloping manometers. The manometer in Figure 1 is affixed to the filler at A , and is yo designed that the legs, B and C, are in the same plane when in use. The trap, D, is slightly below the plane when in use. The tube, C, is constricted at the end within the trap, and the upper end is, as usual, somewhat thickened. Leg C is about 30 cm. long; the other parts are in proportion. To fill, the manometer is baked out under vacuum and the mercury in the 250-cc. bulb, E, is boiled at the same time with the stopcock, F , set as shown. The mercury is permitted to become completely cool and the manometer is then rebaked and cooled. Stopcock F is then turned so as t o admit air slowly into tube G, and the mercury is thus forced over through tube H into the manometer. When the mercury stands approximately halfway in tubes B and C, stopcock F is turned back to the position shown, thus interrupting the mercury stream. The manometer may then be cut off at A . Whenever desired, more mercury may be introduced into bulb E through stopcock F. This type of manometer is particularly useful when it is important that the manometer liquid shall not be a solvent for the gases studied. The constriction a t the open end of tube C reduces the effect of the mercury hammer. The trap, D,is employed because it is found as a matter of practice that, when gases are suddenly introduced into a sloping manometer (as often occurs in use), there is a tendency toward pulling over bubbles into the closed leg. The trap prevents this.
G
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-i 1
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I
I I
I I I
FIGURE1
Any bubbles pulled over collect just below the inner seal and have no effect on the pressure reading. If subsequent sticking is to be avoided, the gage should be thoroughly cleaned before any attempt is made to fill it. The author has used the manometer successfully a t a slope ratio of 25 to 1. The method of filling is, of course, equally satisfactory for the ordinary vertical U-tube manometer.
Literature Cited (1) Burton, M., J . Am. Chem. Sac., 58, 1645 (1936). (2) Cameron, A. E., IND.ENQ.CHEM., Anal. Ed., 5, 419 (1933). (3) Doja, M. Q., S.Chem. Education, 10, 574 (1933). R Z C ~ I V ZApril D 5, 1937
