October 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
(5) Lewis and Randall, “Thermodynamics,” p. 526, McGraw-Hill, 1923. (6) Lewis and Randall, Ibid., p. 522. (7) McClendon, J. Bzol. Chem., 60, 289 (1924). (8) McClendon, J. Am. Chem. Soc., 50, 1093 (1928). (9) McClendon and Remington, Ibid., 51, 394 (1929). (10) McClendon, Remington, von Kolnits, and Rufe, Zbid., 52, 541 (1930). (11) Pfeiffer, Biochem. Z., 215, 126-36 (1929).
377
(12) Remington, McClendon, von Kolnite, and Culp, J. Am. Chem SOC.,52, 980 (1930). (13) Remington, McClendon and von Kolnite, Ibid.,53, 1245 (1931).
RECEIVED April 4, 1932. Presented before the Division of Agricultural and Food Chemistry a t the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 t o September 4, 1931. A contribution from Mellon Institute’s Industrial Fellowship on Iodine, which is sustained by the Iodine Educational Bureau, New York, N Y
Determination of Copper Number of Paper J. D. PIPERAND C. H. FELLOWS, The Detroit Edison Co., Detroit, Mich.
A
N INVESTIGATION into the service deterioration of the oil-impregnated paper insulation of 24,000-volt underground cable led to the use of the copper number test for following the changes which occurred in the paper. I n a series of experiments in which oil and paper were subjected in vacuo to electric discharge (which had been shown to be one of the chief causes of service deterioration), it was found that an increase in the time or intensity of bombardment was accompanied by an increase in the copper number of the paper (12). The copper number was therefore used as an indication of the amount of deterioration. Early tests in 1928 soon demonstrated the necessity of experimental work to modify one of the existing test methods for the determination of this factor so as to obtain a reliable test procedure for the requirements. The method finally adopted (7) has proved exceedingly satisfactory, and although essentially a standard method, the modifications are thought worthy of description as of general interest. A copper number test, to be satisfactory for the purpose mentioned, must be rapid, sensitive, and capable of yielding results which are reproducible within reasonable limits on a sample not larger than 1.5 grams. In addition the apparatus required must not be expensive. Early determinations were made by means of Schwalbe’s method (IS) and some of its modifications, but the results were unsatisfactory. The values obtained were erratic because of the instability of the Fehling solution during the boiling period, and because of the error due to adsorption by the paper of bivalent copper. Differences in paper samples subjected to different deteriorating treatments were not always brought out, probably because of the effect of caustic alkali in modifying the reducing properties of the cellulose (4). I n later work the method described by Braidy (2) and others (9), in which the Fehling solution is replaced by a sodium carbonate-bicarbonate solution, was used with more satisfactory results. As Clibbens and Geake point out (4,the method gives a low and constant blank, is sensitive to slight modifications of the cellulose, and is reproducible within reasonable limits. Finally, the improved Braidy method as worked out by the Bureau of Standards and later published ( 3 ) was found, aft>er minor modifications had been introduced, to satisfy the requirements completely. The Bureau of Standards specified a method of thoroughly disintegrating the paper without heating the fibers in order to obtain more accurate results. The Gault-Mukerji molybdophosphoric acid method (6) of determining the cuprous oxide was adopted. The size of the sample was reduced to 1.5 grams.
MODIFICATIONS OF OLD METHOD The modifications of the Bureau of Standards method are as follows: 1. The shredder recommended by the Bureau of Standards was too large and costly for the type of work being carried out in these laboratories. A Hamilton-Beach malted milk mixer modified in the manner described by the Okonite Callender Cable Company (11) was found to meet the requirements. The shredder is shown in Figure 1. The stirring motor was mounted on a telescoping shaft, A , so that it, together with t h e stirrer, could be raised or lowered to any desired h e i g h t . A variable rheostat, B, was included to control the rate of stirring. A hotplate, C, was i n s t a l l e d for heating the l i q u i d d u r i n g the shredding process. The original stirring shaft was replaced by a brass shaft, D, on which were mounted two shredd i n g wheels 1.5 inches in diameter made from ‘/arinch sheet brass. Each wheel consisted of eight blades whose cutting edges were FIGURE1. PAPERSHREDDER sharDened. The two ;heels w e r e mounted so that the liquid was thrown upwards by the lower wheel and downwards by the upper wheel. The brass fingers, E, are important since they help to throw the fibers constantly into the shredding wheels. When used a t high speed with a hot solution, the disintegration of the paper is complete after one minute. The short time involved eliminates the irregularities attendant upon long continued beating (8, IO).
/'
F
-/---
