Apparatus for Packing Columns with Single-Turn Helices. 0. C. W. Allenby and C. L’Heureux, Central Research Laboratory, Canadian Industries Limited, McMasterville, Quebec, Canada. distillation column by hand with single-turn helices is tedious and time-consuming operation. For greatest column efficiency, the helices must be separated from one another during the packing process and as far as possible introduced singly. To pack even a small laboratory column properly requires a number of hours. A simple apparatus which was designed to overcome this difficulty has been in use for the past 3 or 4 years in this laboratory. The helices are separated by a jet of air qFhich, by whirling them in a round-bottomed flask, untangles them from their neighbors. Single helices then are carried by the air stream up through the neck of the flask and are delivered to the top of the column by a glass tube. ILLINO a
Fa
The a p p a r a t u s consists of a roundbottomed flask, A , of 500-ml. capacity fitted with a 24/40 s t a n d a r d -t a pe r joint (see Figure 1). A side arm, B, is blown into the side of the flask and ext e n d s downward, following the contours of the inside until it reaches almost to the bottom. The end of the tube is flattened to give a broad jet approximately 1 X 7. 111111. in inside dimensions. A piece of glass tubing, C, connects the Figure I flask through a 24/40 joint to.the head of the distillation column. The end of the joint is artially closed by a short section of rubber stopper in which a hok 5 mm. in diameter has been bored, D. In operation, a proximately 25 grams of helices are introduced into the flask ana the side arm is connected to a source of compressed air. Ohly a comparatively low ressure is re uired, several pounds er square inch being s u d i e n t . SuitabTe precautions should {e taken if a source of air under high compression is used because of the possibility of some blockage occurrin in the system with subsequent rupturing of the flask. The air tow is adjusted so that the helices are whirled in a circular motion, thus gradually loosening up agglomerates and producing single isolated helices. If the flow of air is correct, these single helices are carried up with the air current and over into the column. In order to prevent the whirling mass of helices from striking the far lip of the neck of the flask, two elongated depressions are made in the flask just below the neck each at ri ht angles to and on either side of the center of their line of trav8 (E,Figure 2). This serves to deflect the major portion of the helices slightly downward. Of those which pass through the gap, the single helices are carried b the air stream up through the neck and into the column hen the quantity of helices remaining in the flask has been reduced by about one half, refilling to the original amount maintains a smooth circulation. Difficulty may occasionally be encountered on very dry days with static electricity built up as a result of the circulation of the helices in the flask. This can be overcome by moistening the air by passing it through a scrubber filled with water before introduction into the apparatus.
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With the above equipment, a 1.5 X 52 cm. column was packed with single-turn ‘/Finch glass helices in 20 minutes. A total of 34.2 grams of helices was introduced into the column and with a carbon tetrachloridebenzene mixture a t total reflux a plate value of 9 was obtained. To pack the same column by hand required 4 hours of concentrated effort, 33.2 grams of helices were i n t r o d u c e d , and the plate value under the same operating conditions was also 9. The equipment has also been found to operate satisfactorily with 32- to %gage Figure 2 l/lkinch nickel helices. ACKNOWLEDGMENT
The authors are indebted to D. L. Oulton for a number of suggestions and for his assistance in testing the equipment.
Source of Error in Kjeldahl Microdeterminations. W. J. Wingo. 0. L. Davis, and Lee Anderson, M. D. Anderson Hospital for Cancer Research, Houston, Tex. nitrogen determinations by the Kjeldahl micromethod, it is a Iordercommon practice to boil the distillate before titration in to sharpen the end point. Frequently, the water is drained N
from the condenser for a minute or more at the end of the titration in order to “steam out” the condenser. Both practices become sources of error when boric acid, instead of a strong acid, is used to trap the ammonia distilled from the sample. Recently, in a series of Kjeldahl microdeterminations by the method of Miller and Houghton [ J .Biol. Chem., 159,373 (1945)], the distillates were boiled before titration. The boiling sharpened the end point, but the results were invariably low. A search of the literature showed that Markly and Hann [J.Assot. Ofic. Agr. Chemists, 8, 455 (1925)] had studied the loss of ammonia from heated ammonium borate solutions. They found that after heating for 30 minutes there was no loss at temperatures below 50” C., but there was an increasing loss a t higher temperatures; a t 100” only 34.75% of the ammonia remained. Even bringing the distillate to the boiling point entailed a small loss of nitrogen, which increased with the tinie of boiling; 5 minutes’ boiling gave lossw of about 7%. Titration of the distillate without any heating gave results of satisfactory accuracy ; recoveries of 99.5 to 100.3% were obtained on solutions of ammonium sulfate and on a series of amino acids. Because some schemes for Kjeldahl microdeterminations involve a final steaming out of the condenser, this technique was also studied by steaming out the condenser at the end of a distillation routine which was known to give quantitative results. Low recoveries were obtained whenever the distillate was significantly heated by the steam. The dangers to accuracy inherent in heating Kjeldahl distillatea after trapping the ammonia with boric acid have been known for many years, but recent reports on the use of this method have not mentioned this source of error.
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