US838757A - Converting chromates into bichromates. - Google Patents

Description

UNITED STATES PATENT OFFICE.

CHEMISOHE FABRIK GRIESHEIM ELECTRON, .OF FRANKFORT-ON-THE- MAIN, GERMANY.

CONVERTING CHROMATE S INTO BICHROIVIATES.

Specification of Letters Patent.

Patented Dec. 18, 1906.

. Application filed July 9,1903. Serial No; 164.901- v To all] 1072 0771 7115 may concern:

Be it known that I, ROBERT SUoiIY, a subect of the Emperor of Austria-Hungary, residing and having my POSt-Ol'l'lCG address at 1 Jahnstrasse, Griesheimon-the\iain, Gerwhen a neutral solution of chromate is subjected in ltoth compartments of an, electrolytic cell to the action of electricity, the coinpartments being separated from each other by a diaphragm and the anode being of a material not attacked by the solution, While the cathode is of a material which does not reduce the alkali chromate. Bicbroinate and oxygen are formed in the anode-compartment in accordance with the following equation:

K-zOrOi CF04 I lzOT'i 07 while the action taking place in the cathodecompartment results in the formation of caustic alkali and hydrogen in accordance with the following equation:

The yield is from eighty to ninety per cent. of the theoretical when the amount of alkali contained in the cathode solution is not too high. Haussermann has already proposed to convert by electrolysis neutral chromate into bichromate by placing the chromate in the anode-compartment and charging the cathode-compartment with water, (Ding Zeus Polytechnisches J carnal, 288, 161.) This process has the disadvantage of requiring at the beginning of the electrolytic process an electric current of very high voltage on account of the resistance offered to the current by the cathode liquid, and the yield in alkali and bichromate is very poor on account of the passageof OH ions into the anode-compartment. If, however, in accordance with this invention a chromate solution be introduced into the cathode-compartment, a good yield can be obtained with an electric current of low voltage, because the transference of the negative electricity to the anode is effected solely by the CrO ions.

The following examples will show how this invention can be carried out in practice:

In an iron trough connected to the negative pole of a source of electricity is placed a cell made of a material capable of acting like a diaphragm and dividing the trough into two compartments.

Into both the outer (the cathode) compartment and the inner (the anode) compartment a saturated solution of chromate is introduced, and the anode-compartment is provided with an insoluble anodesuch as lead or platinumfor example. The current is then passed through the electrolytic apparatus until the chromate is converted into bichromate. The capacity of the cathodecompartment should be such that the amount of alkali is about one hundred grams per liter after the conversion of the chromate into bichromate is completed. It is also possible to work independently of the duration of the action going on at the anode by causing a circulation of the solutions in the cathodecompartment: To keep the voltage low, it is advisable to heat the bath to a temperature of from to centigrade.

A saturated or concentrated chromate solution is used to give to the cathode liquid a good conducting quality and to make the yield of the caustic alkali and of bichromate so great as to practically attain the theoretical one. The transference of the negative electricity to the anode is eifected at the beginning of the electrolysis only by the CrO ions, and only at or near the end of the process when the alkali has been generated by electrolysis do the OH ions also participate in the conduction of electricity. Only the OrO ions go through. the diaphragm into the anode-space, so that in the anode-space only OrO and Or O ions are present, and as there is no other kind of ions added the yield can only be reduced at the end of the process when in the cathode-space the concentration of the OH ions has become so strong that said ions participate in the conduction of the current and enter into the anode-space.

When the alkaline contents of the cathode solution are sufliciently high, the said solution can be concentrated by evaporation, the chromate still-present in the solution being i thereby precipitated quantitatively while hasbeen wholly transformed into b'i'chromate set forth of converting chromate into ibichrothe alkali. lye that remains has a strength of 50 Baum.

The anode solution can after thechromate be discharged directly into the crystallizing vessel.

Having now particularly described and ascertained the nature of this invention and in what manner the same is to be performed, I declare that what I claim is The method substantially as hereinbefore mate and the simultaneous production of an alkali which consists in introducing a 's'aturated neutral solution of alkali chromate into i the anode xand cathodecompartments of an electrolytic cell separatedfrom each other by a diaphragm, employing as electrodes an anode not attacked by the solution and a cathode which will not reduce the chromate,

I and electrolyzing the solution whereby at the beginning the transference of the negative electricity to the anode iseffected solely by the CrO ions and caustic alkali is obtained inthe cathode-compartment and a pure solution of bichromate is obtained in the anodecompartment.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

g ROBERT SUCHY. V Vitnesses FRANZ HAss AonER,

MICHAEL POLK.