110
INDUSTRIAL AND ENGINEERING CHEMISTRY
stem of the funnel against the porcelain plate and the entire pad forced to the top so that the asbestos layer plus the precipitate could be removed easily. The asbestos pad thoroughly cleaned the sides of the funnel, as it moved up. The asbestos pad was added to the glass wool and the entire mass treated with concentrated nitric acid, as described above. After filtering out the precipitate, it was necessary to examine the filtrate for selenium. To this filtrate, a volume of about 100 cc., were added 125 cc. of concentrated hydrochloric acid which had been saturated with sulfur dioxide. The solution was allowed t o stand for 2 hours; upon filtering no selenium was found. Therefore, t o this solution was added a definite quantity of selenious acid, equivalent t o 1.14 mg. of selenium. After standing 2 hours, the solution was filtered and the amount of selenium obtained checked with the amount added, showing that the solution was initially in the proper condition for the precipitation of selenium. Samples of Bureau Standards steel No. 101 were dissolved in 50 cc. of perchloric acid plus 30 cc. of water and a definite amount of selenium (1.14 mg.) was added in the form of selenious acid. Upon precipitation with hydrochloric acid and sulfur dioxide the correct amount of selenium was found present, showing the accuracy of the iodometric method. Using the method as outlined on the manufacturer’s sample (reported as 0.218 per cent of selenium) the following representative values were obtained: 0.190, 0.191, 0.191, 0.188, 0.193, 0.192, 0.193, 0.188, 0.189, and 0.190 per cent of selenium. These percentages all reduce to 0.19 per cent when two significant figures are reported, as is customary in steel analyses. The manufacturer’s sample was diluted with an equal quantity of Bureau of Standards sample No. 101. An analysis of this diluted sample by the recommended procedure gave values of 0.094 and 0.094 per cent of selenium. Since experiments showed that no hydrogen selenide was evolved by 60 per cent perchloric acid, a sample of selenium steel was dissolved in this strength of acid, by heating to about 85” C. After complete solution of the steel, 125 cc. of concentrated hydrochloric acid saturated with sulfur dioxide were added. After standing for 2 hours the precipitate was filtered, washed, dissolved in nitric acid, and carried through the volumetric procedure as described, to give 0.190 and 0.191 per cent of selenium. These results indicate an alternate procedure for the determination of selenium and furnish a check upon the procedure given. The method of the Carpenter Steel Company was employed on samples of selenium steel and carried to the point where the precipitated selenium was filtered upon a Gooch crucible. At this point, the precipitate was carried through the volu-
VOL. 8, NO. 2
metric procedure and 0.190, 0.193, and 0.194 per cent of selenium were obtained, furnishing additional corroboration of the procedure given. AS for interfering constituents, Bureau of Standards steel No. 101 was carried through the recommended procedure and gave a blank result, It might be expected that a small amount of copper could remain in the insoluble residue and then react with hydriodic acid to yield iodine, but the fact that negative results were obtained in the blank experiment was considered sufficient proof that selenium alone was measured by this volumetric method. For routine work, the procedure could be materially shortened by eliminating the use of the gIass wool and appIying a correction factor of about 0.5 mg. for the selenium which is evolved as hydrogen selenide. Also the precipitation and elimination of small amounts of iron by ammonium hydroxide could possibly be eliminated in routine steel analyses.
Conclusion The procedure given is fairly rapid. A series of 5 samples was analyzed simultaneously in 1.5 hours. The accuracy has been checked by two procedures, and seems adequate. The values are lower than those obtained by the original method of the Carpenter Steel Company, but an examination of the gravimetric method, for such small amounts of precipitate, led to the conclusion that it yields slightly high resu1ts.l
Acknowledgment The need for a method for the determination of selenium in 18-8 type steels was first suggested by G. E. F. Lundell of the Bureau of Standards to L. F. Hamilton of the Analytical Division of the Department of Chemistry of this institute, a t the latter’s request. The authors undertook the investigation after communicating with Berton H. DeLong, metallurgist for the Carpenter Steel Company, Reading, Pa., manufacturers of the type of steel to be investigated. Mr. DeLong very kindly furnished the material for analysis and generously offered to cooperate in every way possible. RECEIVEDOctober 22, 1936. Publication 51, Research Laboratory of Inorganic Chemistry. 1 In a private communication from the Carpenter Steel Company, it is stated that “our figure of 0.218 per cent of selenium is from a routine heat enalyais obtained in our control laboratory;” hence deviations in results of the magnitude observed are only to be expected.
An Efficient Laboratory Extraction Apparatus FREDERICK C. OPPEN, University of Wisconsin, Madison, Wis.
A
SERIES of studies in this laboratory upon the constituents of various seeds has frequently met the problem of eEcient extraction of large quantities of material, Metal apparatus was ruled Out in order to avoid the possibility of contamination; various glass makeshifts proved leaky and inefficient. With low-boiling solvents such as acetone, ether, ethyl ether, etc,, these difficulties became acute. Accordingly, a modified Soxhlet-tYPe extractor (illustrated) was developed which can be duplicated a t moderate expense from parts readily available, This model has been in use for the past year, and has given very satisfactory results. It is described here in the hope that it may prove helpful to others having similar problems.
The extractor is made from a 7-liter Oldberg, or cylindrical, percolator and has a capacity of about 3 k. of seeds. A percolator with a ground upper surface is selected, together with a small desiccator lid of the same diameter, and these are reground to a good fit. Next a large hole for the cork is cut in the lid, preferably with a cylindrical copper tool in a slow-speed drill grade condenser of grinding compound. The main press, using aisrough novel feature an internal which cools and liquefies nearly all vapors before they pass into the percolator, thus reducing loss at the ground interface between the percolator and its cover. In operation, this interface is rendered more nearly solvent-tight by clamping it at two diametral points with large
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~ e ~ ~ ~ ~ ~ $ & n ~, & $ ~ of cold solvent extraction are maintained, often of value where sensitive crude materials are involved. The bulk of vapors is
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MARCH 15, 1936
111
ANALYTICAL EDITION
condensed as in the usual mounted as a permanent asSoxhlet extractor by the large s e m b l y , lowering only the t o bulb t y p e Allihn-type reflux condenser c o n d e ns e r boiler and p e r c o l a t o r for (not shown). o f opprox. filling or e m p t y i n g . The The n u m e r o u s p o t e n t i a l leaks in such a s e t - u p a r e heat source will vary with avoided by substituting the particular solvent used, ground-glass joints for corks but in most cases a water wherever possible. The joint bath heated by an electric connecting the siphon tube to the bottom of the percolator hot-plate i s s a t i s f a c t o r y . is ground in carefully by hand, Where such a bath is used first using d i s c a r d e d glass for long periods of time, the stoppers of suitable size and constant-level device of Wing taper until a minimum of grinding is necessary t o adapt the (1) can be employed to ads t a n d a r d taper joint. The vantage. The riser from the three corks do not cause trouble boiler may be insulated if if they are of fine grain and desired. coated with collodion. W h e r e a s the description A narrow c l o t h bag containing the material t o be exhere given provides for a 7tracted occupies about fourliter percolator of the Oldberg fifths of the volume of the type, any of the p e r c o l a percolator but must not be " tors common in pharmaceuallowed t o pack the interior ( 5,.Flask ) completely, if siphoning is to tical t e c h n o l o g y might be be effective. A c h a n n e l is employed w i t h s u i t a b l e provided by inverting an 80modifications. The internal mm. evaporating dish over the condenser in c o n j u n c t i o n bottom opening and placing several 10- to 15-mm. tubes with g r o u n d - g l a s s joints along the full length of the side of the bag. These may be wherever there is liquid or hot vapor is important in this bent to conform t o the curve of the percolator. The siphon design, whose details may be varied to suit individual contube extends only a small distance above the top of the venience. bag, and must not be larger than 6 mm. in diameter if it is to fill properly. Sometimes the column fails to break .completely after siphoning has stopped, causing the liquid to Acknowledgment trickle over slowly. This prevents thorough extraction of the The writer wishes to thank R. A. Willihnganz for his coupper portion of material, and is caused by surface tension at the exit end of the siphon tube. It may be remedied by grindoperation in designing and constructing this extractor. ing off this end at a 45" angle. The apparatus may be adapted to smaller charges than the maximum by inverting beakers or bottles within the percolator to occupy the excess space. It is most conveniently
Literature Cited L.9IN=* ENG.
CHEM.i
171 630 (1925)*
R~~~~~~~ November 25, 1935.
A Rapid and Efficient Mixer D. H. NELSON, University of California, Davis, Calif.
I
T IS frequently a time-consuming and tedious process to prepare for analysis samples of emulsions and plastics, The horizontal spiral-bit type of mixer has been successfully used in this laboratory and offers some distinct advantages over other methods of preparing such samples. It is very easily assembled by attaching a spiral bit to the horizontal shaft of an electric motor, which should have a speed of 1725 r. p. m. and be rated a t not less than 0.1 horsepower. A drill chuck obtained from any hardware store for approximately $2 is mounted directly on the shaft. The diameter of the motor shaft mu1st be specified in ordering the chuck. The spiral bit may be obtained from any hardware store for approximately 75 cents by specifying a 0.75inch, solid-center, spiral bit. Before using this bit it is necessary to remove the tip, or worm, and t h e two cutters. The bit i s t h e n placed in the chuck. When the motor runs, the bit is turned in the opposite direction from that used when bor-
ing. This motion throws the sample into the bottom of the sample jar which is slipped over the bit. The jar is held in the hand and moved around to facilitate mixing. When the sample jar is withdrawn some particles of the sample may fly off , and are conveniently caught by a piece of tin shaped in a half-circle and placed on the bench over the bit. The author's experience in using this mixer for preparing butter samples indicates the following precautions which must be observed: Use a thick-walled glass salmple jar with a screw cap, straight sides, flat bottom, and a ca,pacity of approximately twice the volume of the sample. Mix the sample for at least 3 full minutes. Since the butter can be mixed at temperatures from 12" t o 25" C., the u s u a l time re uired for properly tempering &e sample can be eliminated. Avoid partial separation of the sample due t o melting around the edges of the sample jar. RBC~IVED December 10, 19361
