404 F&TMAN KODAK COJ~PANY NOTES. [J. I;. I.

forward that the last traces in the order of I per cent. of acid retained by nitrocellulose is not held mechanically but adsorbed, the evidence in favor of this being mainly the effect of heat and of saline leaches, respectively, in accelerating the removal of the acid and changing the course of the curve expressing the rate of re- moval. The use of concentrated saline leaches, notably that of sodium sulphate, is discussed in detail and its application to the purification of nitrocellulose. From special experiments on the combination of pulping with other treatment it is concluded that the effect of pulping is mainly valuable on a large scale in pro- curing uniformity and of little direct effect on the fihres. From experiments on partial reprecipitation of nitrocellulose from ace- tone solutions and centrifugal fractionation, it is considered “ stabilizing treatments ” are less concerned with the chemical destruction of cellulose sulfuric esters and of lower nitrates of cellulose than with peptization and removal of cellulose dex- trin derivatives.

THE ACTION OF SOLUBLE IODIDES AND CYANIDES ON THE PHOTOGRAPHIC EMULSION.

By S. E. Sheppard. [ABSTRACT.]

A RE-EXAMINATION of the fogging action of iodides on photo- graphic emulsions discussed by Sheppard and Meyer in the Photo- gra/$zic Journal (60, 12, 1920) has been made. In a subsequent paper Mr. F. F. Renwick reported the discovery of a red sensitiz- ing action of soluble iodides and cyanides on the emulsion, and attributed the fogging action observed by Sheppard and Meyer to such a sensitizing effect. In the present paper it is shown that with the emulsions used by Sheppard and Meyer bathing )yith potas- sium iodide produces practically no red sensitizing, but that this is effected with the emulsions used by Renwick. .4n investigation of a large number of commercial emulsions showed the effect to be specific to certain emulsions. In discussing the mechanism of such red sensitizing by iodides and cyanides evidence is brought forward contrary to Renwick’s hypothesis and favoring a photo- catalytic explanation ; it is suggested that the orienting effect of the iodine ion of the silver halide crystal lattice modifies the aggre- gation of colloid silver produced by light of short wave-lengths so that sensitizing for longer wave-lengths is effected.

s Communication No. 130 from the Research Laboratory of the Eastman Kodak Company and published in Photo. J., 88, 1922.