October 15, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Discussion of Sources of Error and Suggested Improvement in Apparatus
Very probably the largest source of error in the apparatus as described in this paper lies in the reading of the mercury manometer. It is doubtful if the differences in level can be read with an accuracy greater than *0.2 mm. unless a good grade cathetometer is employed. It is suggested that the initial pressure be read with a McLeod gage registering to 0.5 atmosphere. Such a gage can be read with an accuracy exceeding 0.1 mm. Characteristics inherent in the McLeod gage introduce an error in the precise reading of small pressures. For example, variations in the bore of the capillary may exist. The personal error also enters with the reading of the differences in level of the mercury columns. A discussion of these characteristics is given in the book by Dushman entitled “High Vacuum.” The McLeod gage, the empty portion of the mercury manometer, and the connecting glass tube were not heated at any time in the making of the analysis, although these parts could easily be heated without any modification of the apparatus. The following quotation from Soddy (IS)emphasizes the necessity of this in order to bring about greater accuracy: The value of calcium as a means of producing the highest vacuum depends on its power to absorb almost instantly the gases condensed on the glass walls as soon as the latter are expelled by heating. As is well known, the real difficulty in the production of high vacua depends not as much on the removal of all the original air, which is comparatively easily and quickly accomplished even with a pump, but on the effective removal of the gases which are condensed on the glass walls of the vessel being exhausted, and which tend to recondense in the pump when driven out of the vessel, and to introduce a kind of steady vapor pressure until they have all been removed.
It may be explained that Soddy excluded the noble gases from
225
the vessels which he wished to evacuate by means of calcium. Adsorbed gases may be one explanation of the constant final pressure obtained in the case of hydrogen analyses. This explanation is given weight by the findings of Sherwood (IO), who observed a continuous deterioration of vacuum with time in glass. I n the light of the findings of Kraus and Hurd (4) it is doubtful if unabsorbed hydrogen in the presence of excess of calcium would account for this residual pressure. The spectroscope could be used in establishing the facts in this case. Temperature variation, at the times of the initial and final pressure readings, introduces a small error which could be eliminated by the use of a removable water jacket. There is also a small error introduced through the change in volume of. the apparatus caused by the shifting of the mercury columne. when the sample is absorbed by the calcium. This factor is reduced to a negligible value in the apparatus here described. because of the comparatively great volume of the chamber A , Sieverts and Brandt (18) found it necessary to calculate a correction for this factor in their work because of the small size of their gas samples. Literature Cited (1) Arndt, Bev., 37, 4733 (1904). (2) Ephraim and Michel, Bels. Chim. Acta, 4, 900 (1921). (3) International Critical Tables, Vol. I, p, 393. (4) Kraus and Hurd, J . A m . Chem. Soc., 46,2559 (1823). (5) Mellor, “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. 111,p. 631,Longmans, Green and Co., 1927. (6) Moissan, Compt. rend., 126, 1753; 127, 29, 497,584 (1898). (7) Moldenhauer and Roll-Hansen, 2. aflorg. Chem., 82, 130 (1913). (8) Pilling, Phys. Rev., 18, 362 (1921). (9) Ruff and Hartmann, Z. anorg. allgem. Chena., 111,167 (1922). (10) Sherwood, Phys. Rev., 121 11, 448 (1918). (11) Sieverts, 2. Elektuochem., 22, 15 (1916). (12) Sieverts and Brandt, Z.aflgeu. Chem., 29,402 (1916). (13) Soddy, &‘roc. Roy Soc. (Loladon),TSA, 429 (1908).
Determination of Total Moisture in Carbon Blacks’ C, M. Carson GOODYJ~AR TIRE& ~ ~ u B B B R COMPANY,
fi THE course of
an extended research on various grades of carbon black, determinations of total moisture were made by an adaptation of an old method. The method used was similar to one described by Allen and Jacobs (1) for measuring water in tar. The chief difference in the present method is that small amounts of moisture in carbon blacks must be weighed, whereas the larger amounts in tar could be measured. The difficulties in weighing the evolved moisture are described in the ensuing method of determination. Five grams of carbon black were placed in a 500-cc. roundbottom flask with 25 to 35 cc. of dry xylene and 200 cc. of dry mineral oil. A short air condenser led to the bottom of a 25-cc. distilling flask, which in turn was connected to two or more calcium chloride tubes. The flask containing the sample was heated to 150-175” C. in an oil bath, a stream of dry nitrogen being passed through the apparatus. The water and xylene were distilled into the small distilling flask and thence, by warming in a water bath, into the calcium chloride tubes, the current of nitrogen being continued. It required but B few minutes to remove the water from the xylene, indicated by the disappearance of cloudiness, and the calcium chloride tubes were then connected directly t o the nitrogen line and the gas was passed through until the tubes reached constant weight. Xylene is not adsorbed by calcium chloride and nitrogen does not remove water from it at room temperature during the time required for the experiment. The IReceimd June 13, 1829.
AKRON,OHIO
increase in weight of the calcium chloride tubes is the amount of water in the sample of carbon black. The amount of W a k F thus determined is considerably higher than the 105’ C. oven loss in 5 hours, and indicates that most of the moisture is of the “bound” or “capillay” type. A comparison of the moisture as determined by the xyIene method and the 105’ C. oven is shown in the table: BLACK
TOTAL 105OC. Ha0 LOSS
7
0
BkACE
TOTAL10SOC. H20 Loss
%
%
%
Micronex No. 1 5.75 1.42 High-temperature blackb Micronex No. 2 5.96 1.85 Acetylene black No. 1 Micronex N o 3 5.20 1.56 Acetylene black No.9 Heated Micronex Goodwin 0 98 0.00 Thermatomic (Special) (950’C.)a 4 88 1.79 Lampblack Cabot No. 1 3 54 1 66 Super-spectra Cabot NO.3 5.41 1.57 Zinc oxide. Cabot No. 2 a Heated 10 minutes at 950° C. in a closed crucibb. b Made at 1500’ C. c Added for comparison.
0.87 3.19 3.67 2.50 1.25 6.75
0.30
1.07 0 75
O.O?
0.07 0.35 0.10 3.26
0.10 0 02
The relationship of this “bound” moisture to any physica property of a rubber mix containing the black could not be shown. It is probable that other characteristics of the black, such as adsorptive capacity, particle size, etc., are more effective in causing variations than the amount of moisture. Nevertheless the large amount of water in blacks as compared with that in other pigments, such as zinc oxide, is indicative of their relative adsorptive capacities. (1) Allen and Jacobs, Or&-. Corn. 8th Intern. A p p l . Chcm., 10, 17 (1912); C. A , , 6, 3178 (1912).
