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INDUSTRIAL AND ENGINEERING CHEMISTRY
It is clear that if the amount of chloride present be not large, the amount of bromide found is almost theoretical. High results in the presence of much chloride have been noted by other investigators (9). Bromides i n Presence of Iodides The interference of iodides in the oxidation method of determining bromides is overcome by oxidizing the iodide to iodate (7). The authors have observed that the method described above, when slightly modified, overcomes the interference of iodides, as they are completely oxidized to iodates b y the excess of nitric acid-chromic acid mixture.
TABLE V. DETERMINATION OF BROMIDES IN PRESENCE OF IODIDE KBr Sohtion Taken Ml. 2.0 2.0 2.0 2.0 2.0
KI Added Gram
0.0150
0.0300 0.0450 0.0600 0.0750
NaaSi01
Required, Iz = 2Br
M1. 15.20 15.20 15.20 15.20 15.20
Strength of Na2SzOsused, 1 ml.
KBr in 100 hll. of Found Grams 1.00016 1.00016 1.00016 1.00016 1 00016
= 0.001316
Solution Present Grams 1.0002 1.0002 1.0002 1.0002 1.0002
gram of KBr
PROCEDURE. To the mixture of halides 25 per cent instead of 10 per cent chromic acid was added with nitric acid, thus ensuring complete conversion of iodides to iodate. The rest of the procedure was as described above.
Vol. 14, No. 2
Preliminary experiments were carried out with potassium iodide alone and it was found (Table IV) that no iodine is detected in the carbon tetrachloride extractions. I n Table V are given the results of determination of potassium bromide in the presence of varying concentrations of potassium iodide. The results are self-explanatory. It is evident that the method described can be used safely with great accuracy for the determination of bromides in the presence of iodides and chlorides, provided the chlorides are not present in large amount as in saline waters, “potash salts”, etc.
Literature Cited (1) Baubigny and Rivals, Compt. rend., 124, 859 (1897). (2) Baughman, W. F., and Skinner, W. T., J. IXD.EKG.CHEbf., 11, 954 (1919). (3) Clausmann, Bull. SOC. chem., 9 (4), 188 (1911). (4) Denoel, A., J . pharm. Belg., 22, 179 (1940). (5) Dixon, T. F., Biochem. J., 28, 48 (1934). (6) Edwards, F. W., Nanji, H. R., and Parkes, E. B., Analyst, 61, 743 (1936). (7) Meloche, C. C., and Willard, H. H., J. IND.ESG. CHEM.,14, 422 (1922). (8) Meulen, J. H. van der, Chem. Weekblad, 28, 82 (1931). (9) Sutton, F., “Systematic Handbook of Volumetric Analysis”, London, J. S. A. Churchill, 1935. (10) Swift, E. H., “System of Chemical Analysis”, Now York, Prentioe Hall, 1939. (11) Szabo, Z., 2. anal. Chem., 84, 24 (1931). (12) Weissberger, Proskaner, “Organic Solvents”, Oxford, Clarendon Press, 1935.
An Adjustable Safety Shield ARTHUR FURST, San Francisco Junior College, San Francisco, Calif.
T
HE adjustable safety shield here described was developed b y the writer to overcome the limitations to the arrangement of apparatus when a conventional safety shield is used. The conventional shield consists of either safety glass or wire-encased glass set close to the base legs and rigidly attached to them. protection is afforded at the very bottom where there is no real need, while at the same time the shield protects only a restricted area. The height of the shield is the limiting height of the apparatus. If the arrangement must be modified, the dimensions of the safety shield are a hampering factor. Unless an assortment of shield sizes is kept, only a limited number and types of arrangements can be used.
To give more leeway to the assembling of apparatus and still maintain complete protection, an adjustable, portable safety shield was constructed, using the safety glass from an old automobile wind wing. It was tested by shattering a liter beaker against it from a distance of 4 feet. The glass was enframed in 2 by 4 inch wood, and cushioned by strips of cloth. Into two holes bored in each side were forced the shaft ends of some broken rings. These served to clamp the shield to the ring stands which had been removed from the original iron stands and fastened to large wooden blocks. I
This shield can easily be made higher or lower, and used either vertically or horizontally. Ultimate freedom and flexibility in setting up apparatus are achieved.
