INDUSTRIAL AND ENGINEERING CHEMISTRY
930
done by moistening a weighed amount, for instance, 1 gram, on a glass plate and rubbing it with a spatula. A few cubic centimeters of a protective colloid solution, such as 5 per cent gum arabic, and a small amount of an electrolyte, such as 1 cc. of a 5 per cent barium chloride solution for barium sulfate or zinc chloride or sodium hydroxide for zinc oxide, etc., is
Vol. 16, No. 9
h is measured from the surface of the liquid to the entrance of the side tube. Hence at any given time all particles of radius calculated from Stokes’ law for this time will have reached the entrance of the side tube. By calculating the radii a t successive time intervals the range of particle size settling between these time intervals is obtained. The figures given in Table I for the size range were calculated in this way. This table gives the distribution of the particle size for the particular sample of barium sulfate used.
Analysis of Dehydrothio-ptoluidine Sulfonic Acid’ By H. R. Lee and D. 0. Jones THENEWPORTCo , M I L W A U K EWrs. ~~,
HE titrimetric diazotization of dehydrothio-p-toluidine sulfonic acid according to the usual method has been found difficult owing to the low solubility of both the sulfonic acid and the diazo compound in acid solution. Numerous trial titrations, made by adding varying quantities of nitrite to an alkaline solution of the amine, then acidifying and completing the titration in the usual manner, gave results ranging from 80 to 90 per cent of theory. This led to the attempt to analyze compounds of this type by adding an excess of nitrite to an alkaline solution of the amine, acidifying, and titrating back the excess of nitrite with a standard solution df a primary amine. The first problem in the development of the back titration method was to find an amine, which would be stable in solution and which would diazotize rapidly and quantitatively at 0 C., to be used as a standard solution for the estimation of excess nitrous acid. p-Nitroaniline and nitrocresidine were found to meet these requirements. The former, being a more common laboratory reagent and having greater solubility in acid solution, was considered more su’itable.
T
FIG.4
added as a peptizing agent and the whole mixture rubbed well with the spatula. The mixture is then diluted gradually until it is fairly thin, washed into a graduate and made up to 100 cc., or whatever volume is desired. In this way a very good dispersion can be made. TABLE I-DISTRIBUTION O F
SIZE I N SULFATE
PARTICLE
Time Minutes 10 20 30 40 50 60 70 130 170 320
Radius >7.lu 7.1 to 5 . 0 5 . 0 to 4 . 1 4 . 1 to 3 . 5 3 . 5 to 3 . 2 3.2 to 2.9 2.9 to 2.7 2 . 7 to 2 . 0 2 . 0 to 1.7 1 . 7 to 1 . 2
