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calculated thicknesses of the diffusion layers from the mean value of 0.533 n m . is oiily 5 per cent. This agreement is considered remarkable in view of the difficulty of controlling small cpvection currents and the approximations made in the calculations. It will be noted that by fairly vigorous stirring i t is possible to reduce the film thickness to about one-fifth of its value in a quiet solution. I n view of these facts, the explanation offered for the shape of the curves must be considered as established beyond much question, and it appears that the effective thickness of the stationary film through which diffusion must take place is about half a millimeter in a quiet, solution, though i t can be very greatly reduced by stirring.
APPLICATION OF RESULTS TO
ORGA4XIC. ELECTROCHEMISTRY
Once the foregoing facts are clearly established, the reason for the failure to obtain clean-cut depolarization curves in studying the chlorination of organic compounds becomes fairly obvious. I n organic electrochemistry thc molal concentration of the organic compound in the electrolyte is usually rather low, and the specific rate of diffusion is also generally low because of the high molecular weight. It is therefore difficult to secure clear evidence of depolarization except at very low current densities, even if the reaction rate at the electrode surface is sufficiently rapid. This reasoning does not, of course, apply to cases such as strong acetic acid solutions, etc., where the molal concentrations of the organic compound may be very high. I n order to indicate the magnitude of the current densitier involved, it should be noted that even in a M/4 ferrous chloride solution, the current density corresponding to the maximum 0 355 rate of diffusion in still solutions is only = 0.54 ampere 0.66 per square decimeter, which is far lower than what is generally considered commercially practicable. The great importance of speeding u p diffusion in most organic electro-
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cheniicnl processes therefore becomes obvious. As indicated, the factors which tend to increase the specific rateof diffusion are: (a)high concentrations, (b) low molecular weights, ( e ) rapid stirring, (d) high temperatures, (e) low viscosities. The use of spongy electrode surfaces does not appear promising in view of the relatively great thickness of the stationary diffusion layer. I n many cases, however, the adoption of all these expedients to the maximum degree feasible in a particular case does not carry on the desired reaction with reasonable current efficiency a t current densities high enough to be commercially practicable. I n these cases an expedient which is frequently very helpful is the use of rapidly diffusing carrying agents, which in effect extend the zone of a reaction from a surface to a volume of solution surrounding the electrode. Such carrying agents are generally inorganic salts which form very active oxidation or reduction products at the electrode and then diffuse into the main body of the solution and react with the organic compound. Examples of materials successfully employed in such operations are salts of manganese, cerium, vanadium, and titanium, which can exist in two or more stages of oxidation. It should be pointed out, however, that the mere fact that the depolarization curve soon joins the normal curve for chlorine evolution, as in Fig. 1, does not mean that the desired reaction with the organic compound may not still be proceeding to a very large extent, even a t much higher current densities. I n some cases this may be accounted for by the formation of intermediate compounds-as, for example, hypochlorous acid-which diffuse away from t h e electrode and react with the organic compounds, but in many cases it appears to be primarily due to the increase in diffusion caused by the very effective disruption of the stationary film which results from the evolution of a few gas bubbles. It is therefore impossible to judge the probable success of organic electrolytic reaction by the amount of depolarization shown in curves such as that in Fig. 1.
Dr. Moore Joins Staff of The Dorr Company are vital links, and it is of these that Dr. Richard Bishop Moore, chief chemist and Moore will have charge. mineral technologist of the United States Bu, Dr. ,Moore’s work at Washington has inreau of Mines, has resigned his position and cluded general supervision of all the chemistry on June 1 will take charge of the Developwork of the Bureau of Mines, with direct ment Department of The Dorr Company, charge of the work in nonmetallics, ceramics, Engineers, with headquarters a t its New rare metals, helium, and some of the alloys. York office. He will also act as consulting ’ He built and operated the government raengineer in the many phases of the company’s dium plant a t Denver, and during the activities, where his wide experience and outGreat War was in charge of the construction standing professional reputation will be of and operation of three government helium great value to its clients. plants and of the field work on helium. The Dorr Company is to be congratulated His many other achievements are well known on this important addition to its growing staff to men of science the world over. and on the expansion which is ever bringing He was educated in England and was assoit into contact with a wider range of indusciated with Sir William Ramsay, under whose tries and industrial problems. Beginning in inspiration he decided to make chemistry his metallurgy, its specialization in the handling life work. From 1896 to 1904 he was instrucand treatment of finely divided solids susR. B. MOORE tor in chemistry a t the University of Missouri, pended in liquids has brought it into close and from 1904 t o 1911 professor of chemistry a t Butler College. contact with practically all the great producing industries, and In 1911 and 1912 he was associated with the Bureau of Soils has necessitated a continually broadening field of activity. In of the Department of Agriculture, making a special study of this work the search for new applications of the basic printhe fertilizer resources of the United States. In 1912 he joined ciples of Dorr equipment, the improvement of existing methods and the development of entirely new methods and processes, the Bureau of Mines where he has remained until now.
