INDUSTRIAL AND ENGINEERING CHEMISTRY
170
TABLE I. ANALYSIS OF TYPICAL RESIDUAL FERMENTATION GASES Sample a
b
Gas Analyzed
Oxygen
cc. ...
cc.
Methane %
14.6 14.85 13.8 13.8 9.8
84.3 82.15 84.4 84.0 84.1
79: 6 80.3 83.1 83.1 83.4
Air
a d
5.0 5.0 9.0 9.0
95.0 95.0 91.0 91.0
95.9 98.1 91.2 91.2
Using either air or oxygen for the combustion, the data given in Table I show the analysis of typical residual fermentation gases, after the oxygen, carbon dioxide, and hydrogen had been removed. Generally, oxygen yielded closer duplicate results than air.
Discussion and Conclusions I n the use of the slow-combustion pipet the recommended procedure is to make several passes of the gas over the hot coil (S, 4). To determine the efficiency of this combustion pipet, after removing the carbon dioxide produced during the first four passes, two additional passes of the gas were made. Results of these additional passes showed 0.91 to 2.67 per cent
VOL. 11, NO. 3
(average, 1.61 per cent) residual methane left after the first four passes. These percentages are based on the original sample and conform to plant control practice. The apparatus described in this paper was constructed with the idea of incorporating several desirable features in one combustion pipet and a t the same time keeping the construction simple and inexpensive. These features are: (1) the location of the heating spiral in a tube of comparatively small cross-sectional area; (2) the attachment of the spiral in such a manner that it can be quickly and easily removed and replaced; and (3) the use of a standard ground joint just below the heating coil. This combination of features is a simpIification of the apparatus hitherto used in routine gas analysis.
Literature Cited Bayley, C. H., Can. J . Research, 7,680 (1932). Coquillon, J., Compt. rend., 83, 394 (1876); 84,458, 1503 (1877). Fieldner, A. C., et al., U. S. Bureau of Mines, Tech. Paper 320 (1935). Matuszak, M. P., Gas-Analysis Manual, Pittsburgh, Pa., Fisher Scientific Co., 1934. ENG.CHBM., Anal. Ed., 6, 77 (1934). Matuszak, M. P., IND. Porter, D.J., and Cryder, D. S., IND.ENG.CHEM., Anal. Ed., 7, 191 (1935). Weaver, E. R., and Ledig, P. G., J. IND.ENG.CHEM.,12, 368 (1920). RECEIYED May 21, 1938.
A Flask for Efficient Stirring AVERY A. MORTON, Massachusetts Institute of Technology, Cambridge, Mass.
M
UCH attention has been paid to different kinds of stirrers, but very little to the type of container which is by far the more important. After a considerable variety of stirrers had been tried, all with little benefit because swirling in round flasks kept the heavy particles in an outside belt, the author observed a marked improvement upon changing the shape of the container. I n particular, vertical creases in the side of the flask had a pronounced effect. As many as four creases, each 7.5 to 10 cm. (3 to 4 inches) long by 0.6 to 2.5 om. (0.25 to 1 inch) in depth, tapering in width from 0.3 cm. (0.125 inch) at the innermost part to 3.75 cm. (1.5 inches) at the circumference, have been made in flasks whose capacity varied from 0.5 to 2 liters. The depth of the crease was not proportioned to the size of the flask but depended partly on the speed with which the stirrer was to be operated. For instance, an 0.5-liter flask in which deep wedges had been sunk in the circumference appeared as if sectioned into four parts about a central portion in which the stirrer rotated a t high speed in order to agitate the mixture. Moderately deep creases break up the average swirling but may fail to prevent the funnel-shaped depression about the stirrer when it is operated at high velocity. In operation a stirrer of the propeller type with blades pitched a t about a 45" angle has proved satisfactory. The mixture is usually pushed downward against the bottom of the flask and up between the sections, from whence it falls again onto the stirrer, With thick slurries the stirrer is driven faster and faster until the mixture moves readily. The agitation in such cases is remarkable. Observations on the efficiency of stirring were usually made with a mixture of sea sand and water. With the ordinary flask the sand would collect in belts and layers, depending on the speed of rotation and the position and shape of the stirrer, These results were contrasted with the even dis-
persion obtained in the new flask. I n making sodium sand for use in reactions with sodium in progress in this laboratory, the particles were more uniform and were a third to a fourth the diameter of those obtained in round flasks. Reaction mixtures so thick that the stirrer rotated without appreciable agitation in the ordinary flask were readily mixed, particularly if the speed were increased. A great advantage in all cases was a continued improvement in the results as the rotation velocity was increased. Previously, comment has been made (I) on an improvement in the dispersion of sea sand in water when a square bottle was used. Such containers, however, are apt to crack when heated, have corners in which solid particles lodge, and will allow a funnel to form around the stirrer at high speeds. Rectangular containers overcome the swirling but not all of the pocketing. The author has, however, had very satisfactory r&sults making sodium sand in rectangular apparatus. Baffles placed in beakers also have pockets in which heavy particles can collect. Most of these containers cannot be used readily with experiments in which the mixture must be refluxed or kept in an inert atmosphere. Fortunately the ordinary flask with its rounded bottom, so helpful in avoiding pockets, and its partially closed top, can be converted into an ideal container for stirring with the changes noted above. Construction is relatively easy for any competent glass blower, the principal precaution being good annealing.
Acknowledgment The author is indebted to Mr. Wayringer for his cooperation in constructing different shaped stirrers and these flasks.
Literature Cited (1) Morton and Palmer, J . Am. Chem. Soc., 60, 1428 (1938). RECEIYED November 19, 1938.
