ANALYTICAL EDITION
April 15, 1943
timate of the amount of vanillin present is desired, the color produced by the unknown may be compared in the colorimeter with those produced by known mixtures of vanillin and ethylvanillin during the same Deriod of time.
269
reagent 2 to separate will cause a decrease in the sensitivity of the test. The procedure must be carefully followed, since the addition of too much reagent or of reagent 2 before reagent 1 may lead to erroneous results.
I
The method has been found to detect the presence of a t least 1 mg. of vanillin in the specimen taken for analysis. Coumarin does not interfere. Fresh reagents should be prepared after 2 days, since too much vater and the tendency of
Literature Cited Assoc, 06cial Agr. Chem., oEcid and Tentative Analysis, 5th ed., Chapter XXV, 5(a), 1930. (2) Chenoweth, IND.ENQ.CHEM.,ANAL.ED., 12, 98 (1940).
of
Analvsis of Constant-Pressure Filtration Data J
DAVID J. PORTER University of Missouri, Columbia, M o .
R
UTH, Montillon, and Montonna ( I ) developed the equation (17
+ c ) ~= K(e + e,)
the quantities F can be found for substitution in Equations 6, 7, and 8 for direct determination of C,K , and eo.
(1)
Literature Cited (1) Ruth, B. F., Montillon, G. H., and Montonna, R. E., IND.ENG. CHEM.,25, 153 (1933).
relating the volume, V , of filtrate produced during a given filtration a t constant pressure, to the filtering time 0, the terms C and Bo representing, respectively, the theoretical amount of filtrate and filtering time required to develop the initial press resistance. T o evaluate the constants of this equation they plotted dB/dV against 8,securing the straight line &/dV = 2(V C)/K (2)
+
the slope and I--intercept of which determine K and C, from which Bo is found by substitution in Equation 1. They showed how the determination of the constants may further be simplified by the assumption of a parabolic V-6 relation, permitting determination of the constants from the data of any three instants during the filtration. Herewith is presented an alternate method of evaluating the filtration constants, applicable t o any filtration represented by Equation 1. The working assumptions are that at 0 = 0, I/ = 0, and that the quantities of filtrate are VI and V 2at times 0, and 02, with O2 chosen to be twice el. Substitution of these conditions successively in Equation 1 gives C2 = KBo
(3)
(v,+ c)2 = m e , + e,) . (v2+ CP = m e n + e,)
(4) (5)
Subtraction of Equation 3 from 4 and 5 and substitution of nV1for TT2 give, following some manipulation,
c
- 2 ) / 2 ( 2 - n) = F1V1 - n) = ~ ~ ~ - 2)'/4n(2 - n)(n - 1) = Fa81
= vl(n2
K = v12n(n - 1)/e1(2 60 =
t'1(?~'
~
2
/
(6) (7)o (8)
The relations between FI, Fz, and FS and n are shown in Figure 1 for 1.2 < n < 1.9, with the inset covering the values for n in the neighborhood of 42. To evaluate the constants of any constant-pressure filtration by the use of this method it is necessary to know the amounts of filtrate a t two elapsed times of filtration for which 0 2 = 20,. The ratio of the two values of V gives n, from which
FIGURE1 FILTRATION CONSTANTS, F, FROM
VALUESOF n
~
