INDUSTRIALAND ENGINEERING CHEMISTRY grams of extracted tissues mixed with filter aid and fragments of filter paper. After the ascorbic acid was stirred into the residue, the extractant was added and the suspension was placed in the Blendor. The procedure was then the same as described for the extraction of fresh material. The degree of completeness of extraction of added ascorbic acid was similar to that of the first extraction of naturally occurring ascorbic acid. The total percentage recovered varied from 90 to 101 per cent. Boiled cabbage tissue residue gave about the same percentage recovery of added ascorbic acid as the unboiled residue. A recovery of 99 per cent was made when ascorbic acid was added to the extractant containing Vol. 34, No. 2 no plant tissue and the motor was run at high speed for 10 minutes.Much time and effort may be saved by this procedure, because a large number of workers have been making the ascorbic acid assay by the chemical method.

The surface areas of a number of commercial carbon blacks have been determined by the low-temperature adsorption isotherm technique. Thermal decomposition and other nonimpingement type blacks possess areas of 15 to 64 M2 per gram. Channel blacks commonly employed as reinforcing agents in rubber have areas around 100 M2 per gram. Ink and color blacks range from 100 to nearly 1000 M2 per gram. The color values of these carbons increase with surface area. The relation of iodine and diphenylguanidine adsorption to surface area has also been studied. Iodine adsorption is a direct function of surface area and, with the exception of certain high-volatile blacks, may be used as a direct measure of total surface. The adsorption of diphenylguanidine depends much more strongly on the volatile content of the black rather than its total surface. While rubber reinforcement depends in a general manner on surface area, certain blacks of nearly identical surface vary widely in the properties they impart to compounded rubber. That the state of the surface is probably of equal importance is indicated by the fact that the activity of the surface, as judged by relative ease of oxidation, may vary widely in blacks of equal area.