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on the surfaces. Another contributing factor might be that the wood used in the panels was new, while the painted wall area had a previous mold growth. This dold growth, although partially scraped and washed off in preparing the surface for repainting, nevertheless provided a ready-made source of mold infection for the new paint. A considerable volume of evidence is now a t hand which suggests that under favorable conditions certain types of mold growth, when painted over, can and will come through a nontoxic paint film. This has also been pointed out by Findlay ( I ) . For the above reason, cleaning and disinfection of old moldy surfaces prior t o repainting are important and should be made a part of the repainting procedure (1,7,8,IO). This contention is confirmed by actual tests in which identical paints were applied to a contaminated area, one half of which was first mashed with a disinfectant solution while the other half was not.
Summary and Conclusions Mold growth on interior oil paints is common in industrial plants where a high relative humidity is maintained. The mold growth is never uniform even in any one room, but is heaviest on surfaces where moisture condensation takes place, such as the interior side of cold outside walls, locations near refrigeration pipes, ceilings, etc. Organic matter, vapors, and dust are conducive to mold growth but interfere somewhat with the testing of the moldresistant properties of paints. However, where mold growth develops on the dust deposited over an oil paint, a preserved paint can be relatively easily washed clean, while on a nonfungistatic paint the mold growth becomes established in the paint itself and cannot be washed off. Mold resistance of interior paints should be tested by applying the test paints to carefully selected sections of walls and ceiling on which water condensation is continuously taking place and which are found to be the most heavily con-
taminated areas in the plant selected. The use of wooden panels, even when most advantageously exposed, may give erroneous results due to the difference in conditions between them and the painted surfaces of the building. I n preparing moldy surfaces for repainting, disinfection of the cleaned surface is beneficial, since some molds can grow through a paint film. Without an adequate preservative the paint with a coldcut resin type of vehicle molded as readily as the paint with a vegetable oil type of vehicle. Tetrachlorophenol and zinc tetrachlorophenate were found to be the most effective paint preservatives among those tested. Under extremely severe conditions of testing 3 per cent of tetrachlorophenol and 3 per cent of zinc tetrachlorophenate preserved both an oil and a cold-cut resin type of interior paint for 2 years. The field test confirmed earlier conclusions on the relative effectiveness of fungicides in oil paints as determined by the rapid laboratory method.
Literature Cited (1) Findlay, W. P. K., J . Oil Colour Chem. Assoc., 23, 217 (1940). (2) Findlay, W. P. K., Paint V a r n i s h Production M g r , 21, 135 (May, 1941). (3) Ibid., 21, 194 (July, 1941). (4) Gardner, H . A., H a r t , L. P., and Sward, G . G., Am. Paint Varnish Mfrs. Assoc., Sci. Circ. 442, 242 (1933). (5) Ibid., 448, 11 (1934). (6) Ibid., 464, 135 (1934). (7) Ibid., 475, 1 (1935). (8) Hansen, C., Paint V a r n i s h Production Mgr , 20, 146 (1940). (9) Harry, R. G., Paint M a n u f . , 6 , 309 (1936). (10) Hofmann, W. F., Am. Paint J.,22, 22. 58 (1938). (11) Ludwig, W., Rev. Applied Mycol., 19, 719 (1940). (12) Partansky, A. M., and McPherson, R. R., IND. ENG.CHEM., ANAL.ED.,12,443 (1940). (13) Toch, M., Am. SOC.Bakery Engrs., Bull. 103 (1936). (14) Weise, IC., Farben-Ztg. 39, 412, 444 (1934).
Determination of Small Amounts of Benzene in the Presence of Cyclohexane And of Toluene in the Presence of Methylcyclohexane B. B. CORSON
AND
L. J. BRADY, Mellon Institute, Pittsburgh, Penna.
T
HE method described in this paper consists in measuring the temperature rise ( A T ) caused by the interaction of benzene or toluene with nitrating acid under definite conditions, and reading the percentage of aromatic from a curve relating AT with hydrocarbon composition. Benzene, up to 12 per cent, can be determined by this empirical method without diluting the sample. For higher concentrations the sample must be diluted with cyclohexane, so that AT will not exceed 20 O C. This thermometric method, which depends specifically upon the heat of reaction of benzene with nitrating acid, is especially suitable for the anaIysis of benzene-cyclohexane mixtures resulting from the hydrogenation of benzene. Analysis by refractive index or density is unreliable, owing to the fact that cyclohexane is usually contaminated with methylcyclopentane (1) (CsH12:n'; 1.4264, &' 0.7781; CH3CsHg: 'zn 1.4099, d:' 0.7488). Also, open-chain paraffins often contaminate benzene and the cyclohexane produced from it. The thermometric method gives results which are a t least as
accurate as those obtained from freezing point data. In the analysis of a series of synthetic benzene-cyclohexane mixtures, in which the benzene concentrations varied from 0 to 12 per cent, the average deviation from the mean was 0.06 per cent. The thermometric method works equally well with toluenemethylcyclohexane mixtures; but in the case of xylenedimethylcyclohexane mixtures AT is dependent upon the isomeric composition of the xylene, and therefore, the relationship between AT and aromatic content must be determined for each sample of xylene in question.
Development of Method The variables of acid strength, period of stirring, water content, size of stirrer, initial temperature, and change of AT with time have been studied. The procedure was t o add 50 cc. of a mixture of benzene and cyclohexane (containing 5.2 per cent of benzene) to 100 rc. of nitrating acid contained in a small-necked pint thermos bottle
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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operated by a 3000 r. p. m. electric motor. Using a stirrer with a blade twice as large raised AT by 0.3" C. with a benzene-cyclohexale mixture containing 5.2 per cent of benaene, and this difference corresponds to an apparent increase in the benzene content of about 0.2 per cent. EFFECT OF INITIALTEMPERATURE. It is t o be noted that AT for the reaction of benzene with nitric acid is greater a t 20"C . than a t 30' C., which is opposite to the thermodynamic prediction, because ( d m 1 = AC,, and ACp is negative.
ANALYTICAL EDITION
July 15, 1942
533
16.
12-
a B-
4-
I
2
3 WI. % o f
4
5
6
Toluene
FIQURE5. ACIDHEATTESTDATAFOR TOLUENE-HEXA0
2
a
6
4
wt. % Ot
EYDROTOLUENE 10
12
Initial temperature, 20°,25", and 30' C.
Benzene
FIGURE4. ACIDHEATTESTDATAFOR BENZENE-CYCLOEEXANE
Initial temperature, 20°, 25', and 30' C.
same direction. Presumably this anomalous relationship of AT to initial temperature is attributable to the relative speeds of demulsification at the different temperatures. The benzene was of reagent PURITY OF HYDROCARBONS. quality; the cyclohexane was made from it by catalytic hydrogenation under pressure a t about 135" C. The cyclohexane was shaken with nitrating acid, washed with water, and distilled. Its freezing point of 5.9" C. indicated a purity of 99.7 per cent.
the mixture. The thermometer is placed in the thermos (bulb resting on bottom of thermos) and the temperature is read 10 minutes after stopping the stirrer-i. e., 20 minutes after the addition of the hydrocarbon. The mixture is not shaken nor stirred during the la& 10 minutes. For precise work, not only should the acid and hydrocarbon be thermostated to the same temperature, but the thermos bottle should also be at that temperature (although its heat capacity is small). The benzene content is read from the family of curves corresponding to the data in Table I, and it is to be noted that AT is essentially independent of the initial temperature (20"to 30' C.) up to 1.5 per cent of benzene. Table I1 presents acid heat data for toluene-methylcyclohexane mixtures.
TABLEI. ACID HEATTESTDATAFOR BENZENE-CYCLOHEXANE (FIGURE4) Weight Percentage of Benzene 0.00 0.56 1.08 1.56 3.29 6.38 10.15 12.01
(1)
AT from Initial Temperatures of
200 c. 0.10 1.10 2.07 2.87 5.59 10.82 17.13 20.13
25' C. 0.10 1.10 2.04 2.79 5.40 10.44 16.55 19.44
30' C. 0.10 1.09 2.00 2.70 5.22 10.07 16.00 18.75
TABLE11. ACID HEATTESTDATAFOR TOLUENE-METHYLCYCLOHEXANE (FIGURE 5) Weight Percentage of of Toluene 0.00 1.34 3.50 5.49
Literature Cited Seyer, Wright, and Bell, IND. ENQ.Cmm.,31, 759-60 (1939).
200 c. 0.32 3.96 9.71 15.00
AT from Initial Temperaturea of 25" C. 0.32 3.95 9.64 14.89
30' C. 0.32 3.95 9.58 14.80
De termination of Benzene in Cyclohexane One hundred cubic centimeters of nitrating acid (1 volume of sulfuric acid, d. 1.84, plus 2 volumes of nitric acid, d. 1.42), measured in a 100-cc. volumetric flask, are poured into a thermos bottle, the flask being allowed to drain 15 seronds. The thermometer is placed in the thermos, the bulb resting on the bottom of the latter, and the temperature is read after 2 to 3 minutes (with a ma nifying lens). Fifty cubic centimeters of hydrocarbon sample (neasured in a 50-cc. volumetric flask and a t the same temperature as the acid) are added to the acid in the thermos. An interval timer is started and the flask is allowed to drain 15 seconds. The stirrer is placed in the thermos, with the bottom of the stirring blade about 1.25 cm. (0.5 inch) from the bottom of the thermos, and when the timer reaches 30 seconds the motor is started. The stirrer is run 9.5 minutes and then removed from
CONTRIBUTION from the Koppers Multiple Fellowship on Tar Synthetics. Mellon Institute, Pittsburgh, Penna.
Cleaning Porcelain Crucibles JOHN E. D. CARWARDINE 55 Donald St., Winnipeg, Manitoba, Canada
THE
method described here can save considerable time and confusion by cleaning "burner grime" and marking inks such as ferric chloride from porcelain crucibles. It does not injure the glaze in any manner, but leaves the crucible with a perfectly clean surface. Place the crucible in a dish of fused potassium bisulfate for about 5 minutes. Remove, allow to cool, and wash with hot water.
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