Feb.,
1919
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T H E JOURiYAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Samples of zinc oxide were also purchased a t two paint stores. A few samples of metallic zinc were examinedfor their content of lead. NETHOD O F ANALYSIS
Lead was determined by t h e well-known method of separating as sulfate and weighing as chromate. From 5 t o 40 g. of zinc oxide or zinc were dissolved in water and sulfuric acid, with a slight excess of acid. The volume was usually about I O O cc. for I O g. of zinc oxide. Alcohol ( g j per cent) was added in quantity just short of t h a t necessary t o start precipitation of the zinc sulfate, usually making about one-third of the final volume. The solution was allowed to stand over night; the lead sulfate was filtered off on asbestos, washed with 50 per cent alcohol, and dissolved in ammonium acetate. The lead was reprecipitated as chromate, after acidifying with acetic acid, by adding potassium dichromate solution. After standing over night, the lead chromate was filtered on asbestos in a weighed Gooch crucible, dried to constant weight a t IIO', and weighed. The accompanying table gives descriptions of the samples and t h e results obtained for lead, and also the results of testing according t o the United States Phaymacopoeia. SUM lLlA R Y
For a short time after the beginning of the war it was n o t possible t o procure zinc oxide of the U . S. P. standard produced in the United States. The U . S.P. test for heavy metals will not detect less than 0.0; per cent of lead in zinc oxide. It is possible a t the present time t o obtain zinc oxide which, with respect t o the presence of lead, is of much higher quality than is called for by the requirements of the U . S. P .
these troubles are aggravated since the precipitate and liquid tend t o creep under t h e paper filter, especially if continuous vacuum is not maintained, thus requiriqg a second filtration. I
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BUREAUOF CHEMISTRY
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s. DEPARTMENT O F AGRICULTURE D. C. WASHINGTON,
AN EFFICIENT LABORATORY FUNNEL FOR FILTERING NEUTRAL LIQUIDS, ESPECIALLY THE VOLATILE ORGANIC SOLVENTS B y T. E. ALDRICH Received October 23, 1918
Those w h o have had occasion in the laboratory t o collect precipitates suspended in ether, chloroform, acetone, alcohol, or mixtures of these organic solvents, especially by forced filtration, have no doubt a t times experienced trouble when using the ordinary funnel and especially the Buchner funnel. I n Ihe case of aqueous solutions, the filter paper, after being moistened and pressed closely to the funnel for the purpose of removing bubbles of air t h a t interfere with filtration, adheres closely to the glass and filtration is ordinarily rapid, while in the case of ether, for example, the solvent being volatile passes away rapidly, and channels and spaces are formed between the paper and the funnel; the paper tending to lift from the glass. This is especially true when filtration is interrupted for a short time; in any case the formation of channels and spaces interferes with rapid filtration. When the Buchner funnel is employed
F I G .1
The advantage of t h e funnel t o be shortly described lies in the fact t h a t the filter paper is clamped securely between two plates by a screw thread so t h a t i t cannot lift even when the filtration is interrupted, a n d thus allow the formation of channels and passages f o r t h e liquid and precipitate underneath. There is no necessity for second filtrations, and a more rapid filtration is also effected by this arrangement.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y DESCRIPTION
The funnel is of aluminum and consists essentially .of four parts having the following dimensions: a cast hollow cylinder approximately 4 in. high, 3 l / 2 in' in diameter, '/a in' with a flange a t the top and a heavier one a t the bottom, 'both being on the outside; a plate in. thick, perforated with l / S 2 in. holes (l/8 in. center t o center) extending t o within l / g in. of the circumference:' a ring 9/16 in. wide -and l/g in. thick, threaded on the inside a n d milled on the outside, having a shoulder (or offset) on the upper inside which engages t h e lower upper surface of theshoulder of thecylinder, this latter preventing the ring from passing over the lower end of the cylinder; a coneshaped lower portion with stem having also a flange at the top '/4 in. thick and threaded on the outside so as t o mesh with the threads on t h e inside of the ring. The lower flange of the cylinder, the plate, and the top of the flange of the cone have approximately the same outside diameter as must also the gasket and filter paper to be used. The upper flange on the cylinder is not essential, except for strengthening the same; but the lower is essential as a shoulder of resistance for the ring when the cylinder, plate, cone, gasket, and paper are pressed together, by meshing the ring FIG.2 with the cone. I n preparing the funnel for filtering i t is only necessary t o have the lower flange of the cylinder, the filter paper (placed on top of the plate), the perforated plate, the gasket (placed between the flange of the cone and plate), and the flange of the cone flush with one another, pass the ring with flange or shoulder uppermost over the top of the cone, screwing as tight as necessary t o secure a perfect joint. A key made of hard wood and carrying two slots which engage two offsets shown in the drawing and plate, opposite each other on the lower part of the cone, facilitates t h e operation of tightening a n d loosening the parts. Another smaller funnel having approximately the in. but in which the dimensions 2 3 / 4 in. x I'/~ perforated plate is not separate but a part of the cone has the advantage t h a t the rubber gasket is eliminated. I n this funnel the perforated plate is depressed '/IS in. below the upper edge of the cone flange and brazed in. Here i t is only necessary t o place the filter paper on the top of the perforated plate and screw the ring over the cone. RESEARCH LABORATORY PARKE,DAVISAND COXPANY DETROIT, MICHIGAN ~
Vol.
11,
No.
2
A CONVENIENT AND EFFICIENT DIGESTION APPARATUS FOR THE DETERMINATION OF CRUDE FIBER By HOWELLD. SPEARS Received November 23, 1918
The official method of the Association of Agricultural Chemists for the determination of crude fiber in feedingstuffs calls for the use of a reflux condenser connected t o the digestion container by means of a rubber stopper. The waste of time in connecting and
FIG. 1-THIS PHOTOGRAPH SHOWS THE APPARATUS IN OPERATIONAND THE DRAWINGBELOWMAKESCLEAR THE CONSTRUCTION OR THE CONDENSER FLASKS
disconnecting such a n arrangement, where many determinations are t o be made, and certain difficulties in its manipulation led t o the construction of t h e simple apparatus described herein, which is designed for use with tall beakers as the digestion containers. I t s convenience and efficiency have been proved by several years' satisfactory use in the feedingstuffs laboratory of the Kentucky Agricultural Experiment Station. While there may be a slight loss of water from evaporation during the boiling, on account of the condensers not being attached t o the digestion containers by a tight joint, yet it is believed t h a t the concentration of the solvents thus brought about is not enough t o cause an appreciable error in the results.
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FIG. 2
The condensers are a series of round flasks, with intake and outflow tubes, connected b y rubber tubing, through which flows the water for cooling. They are
