ANALYTICAL EDITION
22
never as great as 1 grain per 100 cu. ft. Thus it, is apparent that this method is as accurate as any in general use, regardless of whether volumetric or gravimetric methods are used.
DISCUSSION The data in Table I1 show that the experimental errors observed are smaller than the maximum error possible due to errors in reading the burets. I n the entire procedure, four buret readings are required. If the burets can be read to *0.02 cc., and if the maximum error is made in all four readings in such a way that they all affect the result in the same direction, the result will be in error by *0.08 cc. This is equivalent to +lo8 mg. of sulfur. If 0.1 cu. ft. of gas is burned, this quantity of sulfur is equivalent to * 1.24 grains per 100 cu. ft., but if a greater volume of gas is burned for a determination, the absoIute error which may be caused by errors in buret readings is reduced proportionately. Another source of error in the determination is the methyl orange end point. This error is indeterminable, but it can be minimized by comparing the color of the solution being titrated with the color of a portion of the solution a t the end point found on standardization of the solutions. An operator with a little practice, however, usually finds no difficulty in determining the end point to within a drop of hydrochloric acid solution, as the experience of operators using the A. S. T. M. method for motor fuels indicates. This represents an error of about *0.7 grain of sulfur per 100 cu. ft., when 0.1 cu. ft. of gas is burned in a determination. Errors in metering the gas burned are common to all methods, and therefore no special mention is required here. These errors have been considered by the Bureau of Standards
Vol. 5, No. 1
Thus, from theoretical considerations, as wcll as from actual determinations, it is believed that this volumetric method is as accurate as any method heretofore used for the determination of organic sulfur in gas. The speed and convenience of the procedure described in this paper is unsurpassed by any of the methods in general use in the gas industry. A complete determination needs to extend over a period of less than 2.5 hours, and claims hardly 20 minutes of the operator’s attention, while a Referee’s determination usually requires from two to five times as long. The A. S. T. M. method for the determination of sulfur in motor fuels has been modified to make it applicable to the determination of organic sulfur in gas. The accuracy of the method has been checked by burning a gas of known sulfur content, and it has been found to be as great as that of other methods in general use. The average error of sixteen determinations, in which the sulfur concentration in the gas was varied from 10 to 75 grains per 100 cu. ft., was 0.45 grain per 100 cu. ft. The convenience of this method is greater than that of any other now in use, and the time required for a determination is about one-fourth that required by other methods. LITERATURE CITED Am. Soo. Testing Materials, Tentative Standards, p. 391 (1930). Bur. Standards, Cire. 48, 129 (1916). Hollinger, 2. anal. Chvm., 49,84 (1910). Huff, Proc. Intern. ConJ Bituminous Coal, 2nd Conf., 1928, Vol. 11, p. 814. ( 5 ) Lieber and Rosen, IND. ENQ.CHEM.,Anal. Ed., 4,90 (1932). (6) McBride and Weaver, Bur. Standards, Tech. Paper 20 (1913). RECEIVEID July 30, 1932.
(2)*
Rubber Beaker Rings for Accelerating Evaporation on Steam Bath J. A. SCHERRBR, U. S. Bureau of Standards, Washington, D. C.
THE
rate of evaporation of a liquid from a beaker placed on top of a steam bath is notoriously slow. If, however, the beaker is supported so that from two-thirds to threefourths of its length is immersed in the bath (Figure l),the rate of evaporation can be increased threefold and made fully as rapid as from a porcelain evaporating dish. A convenient support is a rubber ring which fits the beaker snugly enough to hold it in the desired position, and yet slips on and off easily when wetted.
or Berzelius form on a set of porcelain steam-bath cover rings having the specified openings. The rings must be made from rubber compounded to withstand the action of heat and moisture, because ordinary grades of rubber deteriorate in a few days on the steam bath. A satisfactory fomuIa, in parts by weight, is as follows: Crude rubber 100 Zinc oxide “Kadox” variety 100 Phenyl-p-naphthylamine 1 Stearic acid 2 Tetramethylthiuram disulfide 3
-
Total
FIGURE 1. BEAKERSUPPORTED BY RUBBERRING
The size of the ring is determined by the size of the beaker and the difference between the outside diameter of the beaker and the next larger opening in the steam bath. The inside diameter of the ring should be 3 to 5 mm. smaller than the outside diameter of the beaker in order to hold it firmly, and the sectional diameter must be large enough to seat the beaker snugly. The schedule of sizes shown in Table I is suitable for rings to be used with Pyrex beakers of the usual
206
Rings of this composition made and vulcanized for 30 minutes a t 125’ C. showed no swelling, tackiness, or other evidences of deterioration after 500 hours’ use on a steam bath. TABLEI. SIZESOF SUITABLE SIX-RING SET BEAKER^
Capaoity
MZ. 150 250 400 000 800
1000
Outside diam. Mm. 67 68 77 88 99 107
RUBBER RINGS STEAM-BATH Inside Outside O P ~ N I N G diam. diam. Mm. Mm. Mm. 63 54 72 80 65 96 80
111 111 111
74 86 96
104
90
120 120 120
RECEIVEID August 19, 1932. Publication approved by the Acting Director of the Bureau of Standards of the U. S. Department of Commerce.
