ANALYTICAL EDITION
3.58
Microabsorption Spectra CHARLESR. NAESERAND B. S. HOPKINS Chemical Laboratory, University of Illinois, Urbana, Ill.
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N THE study of rare earths frequent use is made of absorption spectra to detect the presence of members of the group and to determine the purity of materials. Satisfactory absorption spectra of small amounts of liquids may be made by using a glass capillary tube as the solution container and passing light longitudinally through the liquid. Capillary tubes for such use must be straight and thin walled. Ordinarily used methods do not produce satisfactory tubing. However, by using a specially n designed electric furnace, satisfactory tubing can be made. The furnace was made by wrapping a short length of 10-mm. soft glass tubing with asbestos paper. Six turns of nichrome wire were wrapped around the tubing and paper, with about 1-mm. space between turns. The wire was covered with several coats of alundum cement, amtde time being allowed for dry& each DIAGRAM OF APPARATUS coat before the next was applied, After the last layer of cement was dry, it was wrapped with asbestos paper, which, in turn, was wound with asbestos cord. The ends of the nichrome wire were connected with an electrical circuit which was allowed to flow until the furnace became red hot inside. The current was then turned off and cold water was poured into the red hot, soft glass tube. In this way the glass was shattered, facilitating its removal with a bent wire. The furnace was now ready for use. If the furnace is set up in a vertical position, and a piece of 3- to 8-mm. glass tubing suspended down through the center of it, a very straight capillary may be made by allowing the furnace to heat up and soften the glass. The glass will draw itself out by its own weight and drop vertically. When the glass has cooled, it should be cut so that it will give a capillary and tubing about 5 em. in length. The tube is cleaned and silvered in the usual manner and the silver removed from the inside. Since the opening of the capillary is very small, it does not allow a large amount of light to enter the solution, and thus gives rather poor results at the spectroscope. This difficulty is eliminated by using a very bright source of light and a line focus lens. The lens is so adjusted that the line focus is parallel to the slit in the spectroscope, and lies just inside the end of the capillary. The line focus lens consists of a clear glass test tube full of water or carbon disulfide. The spectroscope used with this apparatus is the directvision instrument which is equipped with a comparison prism. This construction permits the comparison of two spectra in the same field, In this way the intensity of the absorption bands in a solution under examination may be intimately compared with that of the bands in a standard solution. Photographic records may be made if desired. The sample of the unknown is dissolved in a minimum but known volume of solvent, usually about 2 cc., and a known amount is placed in the capillary, By comparison with the spectra of a series of standard solutions the analysis of the unknown may be made, The apparatus is set up as indicated in the diagram. +
Vol. 5 , No. 5
This set-up was used in a study of the separation and purification of neodymium and praseodymium, and was capable of detecting 0.00005 gram of neodymium. It is quite true that other spectroscopic methods are more sensitive, but they are more complicated and involve loss of the sample. A polished platinum capillary might be substituted as a modification of this apparatus. The apparatus can be used in studying the absorption spectrum of any soluble substance, and is especially useful in rare earth work, RECEIVED July 3, 1933
An Air Trap for Water Lines LEO LEHRMAN AND ELVINA. KABAT
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Chemical Laboratory of the City College of New York, New York, N. Y.
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N THE course of some experiments requiring rapid dialysis, use was made of a modification of the concentrating dialyzer (2) devised by F. E. Kendall (1) of the College of Physicians and Surgeons and Presbyterian Hospital, New York, N. Y. It was noticed, however, that the air carried in the water line invariably emptied the vessel overnight, thus slowing up the process. In order to overcome this drawback a trap was devised which effectively removes the air,
WATER t AIRTO SINK
13mrn.
WAT€R FROM LINE This simple piece of apparatus can be used wherever a constant stream of water, free of air, is required. The only precaution is that the water must run in sufficiently fast so that it is constantly flowing through the arm leading to the sink, as well as that leading tos$he apparatus.
LITERATURE CITED (1) Kendall, personal communication. (2) Simms, J. ErptE. Med., 51, 319 (1930) RECEIVED June
2 , 1933.
