INDUSTRIAL AND ENGINEERING CHEMISTRY
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some differences in these values, and that the 0.02 N potassium hydroxide be frequently checked against a standard acetic acid. As previously indicated, the method, with few exceptions, has given uniformly good results with all compounds upon which it has been tried. These exceptions, however, indicate its limitations, for unsatisfactory results are obtained with substances that react with alkali to give products which upon acidification are volatile with steam and will affect the titration. The results with acetylsalicylic acid presented in Table I are included to illustrate this point. Under the conditions of the experiment salicylic acid is somewhat volatile, and that which passes over is titrated with the acetic acid. This difficulty, however, could be overcome in many cases by running a blank upon the unacetylated mother substance and deducting the results from the values obtained upon the acetyl de-
rivative. It is also possible that 0-acetyl compounds may be encountered which react slowly because of their insolubility, but which would react upon longer boiling. I n such cases correct results should be obtained by running a blank upon the reagents under the conditions of the experiment and if necessary applying the above suggestion. Notwithstanding these limitations, which are not of frequent occurrence, the method is believed to be a valuable analytical tool.
A New Sealed Stirrer for the Laboratory
Automatic Leveling Device for Gas Collection by Downward
LEO S. POWELL, Rutgers University, New Brunswick, N.J.
Displacement of Mercury
A
Literature Cited (1) Clark, E. P., J. Biol. Chem., 78, 159 (1928). (2)Elek, A.,and Harte, R. A., IND.ENQ.CHEM.,Anal. Ed., 8, 267 (1936). Comprehensive bibliography. (3) Perkin, J. Chem. Soc., 87, 107 (1905). RIQCEIYED October 3, 1936. Presented before the Miorochemical Section a t the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa.,September 7 to 11, 1936.
NEW sealed stirrer haa been developed which eliminates the use of a mercury seal. This stirrer has been used
by the author and found to be completely satisfactory for the preparation and reaction of Grignard reagents. The materials needed are easily obtainable in any chemical laboratory and the whole stirrer can be made and assembled in one hour. The eccentric drive, A , is made from an ordinary No. 12 solid rubber stopper by drilling a hole through the center for the motor shaft. Another hole at about 2.5 om. from the center acts as a bearing for the glass shaft, B, which is made from a 6-cm. piece of ordinary soft-glass rod of 4-mm. diameter, by heating one end and pressing it against fl a piece of asbestos board so as to produce a flange on the end which prevents it from falling through A . Shaft B should fit loosely enough into A so that it can rotate freely and may be lubricated with a drop of paraffi oil. Part Cis made from a piece of glass tubing of 11-mm. diameter and 6-cm. length, and is flanged at both ends in the manner shown. By lacing stirrer E inside of C anfrotating it by hand, one can determine to what extent tube C must be flanged. D is a piece of soft-rubber tubing fitted over C, forming the seal between E and C. F is a short piece of rubber tubing connecting the eccentric drive, B, to the stirring rod, E. In setting up the stirrer it is essential to place a good clamp around the upper part of C. This diminishes vibration and also prevents the stopper, G, from working loose. The dimensions given are by no means rigid and may be varied to suit the conditions. The advantages that this stirrer offers over the ordinary mercury-sealed stirrer are: (1) It produces agitation which is as efficient, if not more so, than that produced by the mercury-sealed stirrer. (2) The same stirrer may be made to fit any size flask by simply changing the size of stopper G and adjusting the position of rod E. (3) It is simple and easy to make and eliminates the use of mercury. R B C E I V ~August D 10, 1936.
LYNN D. WILSON Marquette University, Milwaukee, Wis.
I
N THE collection of gases by downward displacement of
mercury, manual control of the leveling flask is precluded when the gas evolution is very slow. The difficulty is readily removed by means of an automatic spring control as shown in the accompanying figure. The Pyrex collecting and leveling flasks are of the same dimensions and are mounted on felt-covered wooden supports. Heavy wire connects the blocks holding the leveling flask. The spring is suspended from a rod clamped to a ringstand, so that the starting levels may be adjusted. Analysis of the dynamics of this arrangement shows that flasks of constant cross-sectional area must be used; hence the starting levels must be adjusted to a position where f u r t h e r change in level will not be accompanied by a change in cross section. If t h e force contant of the spring is s u i t a b l e a n d the rubber tubing connecting the flasks is sufficiently flexible, the gases may be collected a t atmosp h e r i c pressure to within 1 to 2 mm. The apparatus may be used for other pressures by applying suction or pressure to the leveling flask. R ~ C ~ I TAugust ~ D 1936.
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