ANALYTICAL CHEMISTRY
904
by different analysts were not always in good agreement. Modification of thymolphthalein by the addition of 1-naphtholbenzein gives an indicator having a distinct color change which easily can be reproduced to within 0.05 ml. of titrant. A reaction time of 20 minutes ensured complete oxidation of the glycols listed in this report. At the initial p H of 0.1 M sodium periodate solutions (pH 5 ) , the reaction with ethylene glycol is complete in 10 minutes a t room temperature (25" It 2"). Price and Kroll ( 4 ) have shown that simple glycols react at a faster rate than do sterically hindered glycols. It is advisable, therefore, when the analytical procedure is applied to unusual glycols, to establish the time required for complete oxidation by preliminary trial. Increase of the inflection slope at pH 9.7 with decreasing temperature is explained by the periodate hydration equilibrium described recently by Crouthamel et al. ( 1 ) . These authors ehowed that in aqueous solutions an equilibrium exists between the metaperiodate and the paraperiodate ions (Equation l), and that the latter ion is favored at lower temperatures. Thus, the hydrogen ion concentration of the solution is effectively increased and the inflection a t p H 9.7 approaches that given by a strong acid. Where samples containing glycerol or other glycols with a similar structure are to be analyzed, it has been found more accurate to make two separate determinations as described in the analytical procedure. Replicate analyses of a glycerol solution
by the recommended procedure gave results agreeing to within 0.2%, between the formic acid analysis and the periodate analysis. For analyses in which the excess periodate was not destroyed before titration for formic acid, agreement was only to 1.0%. The effect of an organic acid in the sample can be compensated for by a separate titration of a sample aliquot to the mixed indicator end point and correction of the periodate titration in the same manner as for formic acid. Weak bases present a different problem and samples containing these compounds cannot be analyzed by the present method. ACKNOWLEDGMENT
The authors wish to express their appreciation to John Mitchell, Jr., for his interest in this work and to Ella Mae Gardner for performing a large number of the analyses reported. LITERATURE CITED
(1) Crouthamel, Hayes, and Martin, J. Am. Chem. Soc., 73, 82 (1951). (2) Malaprade, Ann. chim., (10) 11, 104 (1929). (3) Malaprade, Bull. soc. chim., (4)43, 683 (1928); ( 5 ) 1,833 (1934). (4) Price and Kroll, J. Am. Chem. Soc., 60,2726 (1938). ( 5 ) Smith, "Analytical Applications of Periodic Acid and Iodic Acid and Their Salts," 5th ed., pp. 50-62, Columbus, Ohio, G. Frederick Smith Chemical Co., 1950. RECEIVED for review October 24, 1961.
Accepted December 13, 1951.
Alignment of Roller Analyzers GEORGE L. MATHESON, Standard Oil Development Co., Linden, N . J .
THE Roller method ( 2 , 3 ) of classifying powders to determine particle size distribution is commonly used ( 1 ) for the subsieve size range. Because it is an air-elutriation process, the classification is based on the free fall velocity of the particles. In the petroleum industry much use of it is made for determining the relative size distribution of cracking catalyst employed in the Fluid process. Its application is gradually being extended well into the sieve range; several air velocities are used in the 1.125inch inside diameter tube or rhamber. Several factors govern the degree of reproducibility of the data. One of these, not heretofore generally appreciated, is the precision with which the 1.125-inch inside diameter chamber must be aligned in a vertical position. Visual observation with a glass tube approximately 1.125 inches in inside diameter indicated that slight inclinations from the vertical position influenced the concentration of particles reaching the top of the chamber to a surprising degree. At the same time there was no apparent change in concentrations prevailing in the lower sections of the disperse phase, As the elutriation of a cut is terminated when the overhead yield decreases to a given rate-e g., 0.1 gram per 10 minutes for a 10-gram sample-this factor will influence the amount of entrained particles collected. In order to determine the influence of slight inclinations from the vertical position, Roller tests were made with chambers 1.125 and 2.25 inches in inside diameter. A modified aeration tube ( 1 ) with a fritted disk was used instead of the regular U-tube with air jet. Two narrowly classified powders were used, so that entrainment rates could be maintained in each chamber over several 10-minute periods while blowing the powder with 9.7 liters per minute of air. The vertical alignment of the Roller tubes was varied for each successive period, as given in Table I. The alignment was measured by comparison with a nearby plumb bob and line; alignment was checked in two directions at right angles to each other. The test consisted of measuring the weight of catalyst entrained from the tube in successive 10-minute periods without putting the entrained catalyst back into the apparatus. The differences in entrainment shown for the 1.125-inch tube will markedly affect the yields of the various cuts, with a conse-
Table I.
Tube Size, I . D . , Inches 1.125
2.25
Influence of Roller Tube Alignment on Entrainment (Air flow, 9.7 liters per minute) Tube Alignment, Deviation from Vertical Entrainment per Inch per 10-Minute Period 28 inches Degrees Gram
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