44 REPORTS ON THE STATE OF SCIENCE.—1918. 
by Ormandy, 15 contained less iron after purification while 8 con- 
tained more. 
Shortly before the war, Schwerin organized the Hlektro-osmose 
Aktien Gesellschaft of Frankfort-on-the-Main, for the purpose of 
developing his multiplicity of inventions, commencing operations 
with a capital of three million marks.2° Several improvements and 
changes have been made in the clay process since that time, along 
the lines of adding negative colloids (silica, humus) to the clay 
suspension,?”” employing electro-osmotic’ pressure filters,°* using 
diaphragms” differing (1) in size of pores, (2) in sign and intensity 
of interface potential, and making several changes in the “ osmose” 
machine itself. There is not enough available information for one 
at the present time to evaluate those modifications. The process as a 
whole appears to be far the most promising one Schwerin has 
developed. 
ELECTRICAL TANNING. 
Electrical tanning*’ of leather is the oldest practical application of 
electrical endosmose, having been originated, according to Buse, by 
Grosse in 1849. In 1874 de Meritens at Petrograd used electricity in 
600 tan pits, employing a layer of carbon at the bottom as anode, 
placing on this alternate layers of hides and tan bark and concluding 
with a sheet of zinc as cathode. Buse decribes other systems ( Groth, 
Worms and Bale, etc.) and reports that the electric current increased 
the rate at which tannin was taken up from 338 to 533. 
So far as one is able to judge, electricity has been applied to 
tanning processes for two purposes (1) to hasten the process by 
heating the bath electrically, (2) to hasten the process electro- 
osmotically by the tan liquor into and through the skins. For the 
first purpose either direct or alternating current may be used, but for 
the latter only direct current can be employed. It seems incorrect 
to advocate as Williams does the use of an alternating current to 
produce the endosmotic effect of a direct current without at the same 
time causing electrolytic decomposition of the tannins. 
The electro-osmotic method of tanning is decidedly more rapid 
than the ordinary diffusion process and would bea distinct success 
were it not for anodic oxidation of the tannin. Schwerin*! has 
endeavoured to prevent this by surrounding the electrodes with dia- 
phragms but his- process and apparatus appear to be excessively 
intricate. It ought, however, to be possible to solve all these 
difficulties, for it is undoubtedly in this field and in impregnation in 
general that electrical endosmose should find widest and most 
successful application. 
26 Hiektrotechn. Zeit., 35, 860 (1914). 
*7 Brit. Pats. 27931 (1911), etc. 
28 Brit. Pats. 23545 (1912). 
29 Brit. Pats. 2466 (1912). 
30 Folsing : Zeit. Hektrochemie, 2, 167 (1893); Rideal and Trotter: Jowr. Soc. 
Chem. Ind., 10, 425 (1891); Buse: Zhid., 19, 57 (1900); Rideal and Evans: Jbdid., 
32, 633 (1913); Williams: Jour. Am. Leather. Chemists. Assoc., 8, 328 (1913); 
Groth: Brit. Pat. 19239 (1912). 
31 Brit. Pat. 21190 (1914). 
not hae an 
