1116
ANALYTICAL CHEMISTRY
port, angelica, sherry, sauterne, and claret wines to which known amounts were added after treatment to remove the small quantities of iron present. Figure 1 shows several typical papers obtained from tests on the aqueous solutions. Wines containing as little as 2 micrograms of potassium ferrocyanide per ml. gave definite positive tests when 1 ml. of the mixture was tested and very strong tests when 5 ml. were tested. Blank tests on all grape wine distillates and grape nines before addition of hydrocyanic acid or potassium ferrocyanide indicated that hydrocyanic acid does not occur in them naturally. The presence of naturally occurring hydrocyanic acid in peach brandy, however, and in distillates from peach wine and plum wine \vas demonstrated. This suggests a possible use for the method as an aid in distinguishing peach and plum wines and brandies from those made from grapes. berries, and other fruits. For quantitative tests, Gettler and Goldbaum used flanges of three different sizes, the choice depending on the concentration of hydrocyanic acid in the sample. In testing wines the 4-mm. flange is recommended because it is most suitable for the detection
of quantities near the lower limit of sensitivity of the method. Jl'hen larger quantities are encountered, the sample may be diluted or a smaller portion taken for the test. Flanges may be procured from several manufacturers (2). Orders should specify that the size of the flange is gaged by the diameter of the circle forming the inner edge of the ground portion of the flange, rather than by the inside diameter of the tubing. ACKh-OWLEDGMEh-T
The helpful suggestions and criticisms given by R. F. Love and G. E. llallory of this laboratory are gratefully acknowledged. LITERATURE CITED
Analysis," 5th ed., 1'01.VIII, p 5 i i . Philadelphia, P. Blakiston's Son & Co., 1930. (2) Gettler and Goldbaum, ANAL.CHEM.,19, 270 (194i1. (3) Kolthoff and Pearson, Ibid.,3,381 (1931). (1) "Allen's Conirnercial Organic
RECEIVED December 15. 1947.
Advantages of Butyl Rubber in Organic Analysis ALSOPH H. CORWIN
AND
CLARENCE KARR, JR., The Johns Hopkins University, Baltimore, M d .
H E fact that Butyl rubber has approximately lOy0 the T permeability of ordinary rubber to air (2-4) makes it a logical choice for connections in the Dumas apparatus for the determination of nitrogen. The superiority of this tubing is easily demonstrated by substituting samples of various types of tubing for the combustion tube in the apparatus. -4sample of carbon dioxide of predetermined size is swept through the tubing and the size of the blank is measured in the nitrometer. The blank ratio of 1 for Butyl rubber to 8 to 12 for natural rubber will be obtained with tubing of comparable size. For the past 2 years, the use of Butyl rubber has been standard in this laboratory in the Dumas apparatus and a diminution in the blank has been regularly obtained because of this. Table I. Tubinr Natural Butyl Silicone
Permeability of Rubbers CO? Diffused, Y 13.005,13,040 176. 157 13,488,12,841
H20 Diffused. Y 131,100 65,56 578,647
The literature also indicates that permeability of Butyl rubber to carbon dioxide is smaller than that of natural rubber (1, 2). It is of interest to learn whether or not this superiority also extends to water vapor, with a consequent advantage in the determination of carbon and hydrogen. Experiments, summarized below, show that while the superiority of Butyl rubber tubing is marked in the case of carbon dioxide, it is small but measurable in the case of water vapor. The apparatus in which comparisons of permeability were made consisted essentially of a jacket made of glass tubing of lar e diameter and stoppered with rubber stoppers. Two inlet and outlet tubes and a thermometer were introduced through the stoppers. To one set of inlet and outlet tubes, the sample of rubber to be tested was attached. The other set was used for the introduction of the gas to be tested for penetrating power. Oxygen free from water and carbon dioxide was swept through the rubber tube a t the rate of 10 ml. per minute for 50 minutes. Water or carbon dioxide passing through the walls of the tubing was absorbed with Anhydrone or Ascarite in a weighed absorption tube. A testing atmosphere saturated with water vapor was obtained by bubbling oxygen through distilled water in a Friedrich's spiral type condenser. Dry carbon dioxide was obtained by passing the tank gas over Anhydrone. All rubber samples were 282 mm. long and all were analyzed at room temperature, approximately 26-27' C. Table I shows the results obtained on a sample of natural rubber (No. 1 Garlock soft black tubing), one of Butyl
rubber (obtained through the courtesy of Esso Laboratories, Standard Oil Development Co., Linden, N. J.),and one of silicone rubber (obtained through the courtesy of General Electric Co., Schenectady, S . Y.). ApproximatP diffusion coefficients were calculated by the following formula : = 2.3 W log n / r l 2TCl Lt where k is the diffusion coefficient, W the average weight of material passing through the wall, r~ the outside radius and r~ the inside radius of the tubing under test, C1the outer concentration of carbon dioxide or water, L the length of the sample, and t the duration of the experiment. It is assumed that the inner concentration of carbon dioxide and water is maintained a t zero by the sweeping. Table I1 gives a comparison of the necessary constants and of the diffusion coefficients. High precision in the absolute values of these diffusion constants is not claimed. The authors do feel justified in concluding that there is a marked advantage to be gained by the use of Butyl rubber tubing in making the connections on an analytical train for carbon and hydrogen. This advantage will be greater in the case of carbon dioxide and smaller in the case of water. Butyl rubber tubing may be obtained from the Continental Rubber Works, Erie, Pa. Table 11. Comparison of Constants wco2, g . WHzO, g.
rz, mm. rl. mm. Clcoz, atm. Clmo,atm. L, cm. t , sec. kcoz X 1O'Q kH20 X 1010
Natural 0,013,023 0.000,116 3.85 1.35 1.0 26/760 282 3000 25.2 6.41
Butyl 0.000,167 0.000,061 4.35 1.05 1.0 26/760 282 3000 0.47 4.66
Silicone
LITERATURE CITED
(1) Davis, Donald W., Paper Trade J.,123,No. 9,33-40 (1946). (2) ?worth and Baldwin, Ind. Em.Chem., 34, 130J (1942). (3) Lightbown, Verde, and Brown, Ibid., 39, 141 (1947). (4) Thomas, Lightbown, Sparks, Frolich, and Murphree, Ibid., 32,. 1283 (1940). RECEIVED June 17, 1948.
