US734950A - Manufacture or peroxid of lead. - Google Patents

Description

No. 734,950. PATENTED JULY 28, 1903.

B. QUBDENFELDT. MANUFACTURB 0F PEROXID 0F LEAD. l,APPLICATION FILED JUNE 25, 19o1.

No MQDBL.

fafk au H UNITED STATES Patented lTuly 28, 1903.

PATENT OEEICE.

ERWIN QUEDENFELDT, OF DUISBURG, GERMANY, ASSIGNOR TO CHEM- ISCHE FABRIK GRIESHEIM ELEOTRON, OF FRANKFORT-ON-THE-MAIN,

GERMANY.

MANUFACTURE OF PEROXID OF LEAD.

SPEQIFICATION forming part of Letters Patent No. 734,950, dated July 28, 1903.

` Application filed June 25, 1901. Serial No. 65,993. (No specimens.)

of Lead, of which the following is a specifica-v tion.

The process forming the subject ofthe present invention is characterized by the direct conversion of lead oxid (litharge, red lead, and the like) into lead dioxid. This conversion is effected in a concentrated solution of an alkali chlorid or of a chlorid of an alkaline earth forming an emulsion with the lead oxid, the mixture being electrolyzed at a pressure of about three volts and a corresponding current intensity b v means of'an insoluble anode-such as platinum, carbon, or the like-and a cathode of any metal, which is preferably fitted int-o a frame over which parchment-paper or other suitable materi al is stretched, or which is separated fromv the anode by any other suitable diaphragm. No trace of chlorin is evolved at the anode,

while a brisk disengagement of hydrogen takes place on the cathode without any appreciable deposit of spongy lead. The lead oXid, which is kept in constant motion, becomes gradually brown and toward the end of the electrolytic process becomes black brown. The conversion of the lead oxid into superoxid takes place quantitatively in the time calculated from the current intensity required for the oxidation. By shortening the time of this reaction it is possible to obtain in the reaction product any required amount of lead dioXid.

The transformation of lead oxid into peroXid by this process is as follows: Lead oXid being but very imperfectly oxidized todioxid by hypochlorous salts, it is to be supposed that in the present electrolytic process the hypochlorite that is formed does not act directly on the lead oXid contained in the emulsion, but on the compound of alkali and lead oxid,

ONa (Pb/ \oNaJ which must be formed as an intermediate product and pass into the solution. In th'is resides the great advantage possessed by this process over those hitherto known, for according to the older methods a salt of lead in solution must always be caused to act on the hypochloroussalts, so as to obtain a large percentage of dioXid, this salt being either lead chlorid or lead acetate; but with the process forming the subject of. this invention no special preliminary dissolving operation, either in acetic acid or hydrochloric acid, is needed, for the alkali, which is always present in small quantities in the present electrolytic process, will dissolve corresponding quantities of the compound of alkali and lead oXid, which are then at once converted by the hypochlorite or by chlorin into lead dioxid and alkaline chlorid, as the following equation shows:

ONaOl Pb/ An advantage possessed by the improved electrolytic process over those hitherto known is that the dioXid is not deposited directly on the anode, which would cause it to be of crystalline texture, and that being formed in a state of emulsion it assumes a perfectly pulverulent form.

In the accompanying drawings is illustrated one form of apparatus which may be used, and in whichl Figure l is a vertical sectional view of the apparatus, and Fig. 2 is a plan view thereof.

The new process may be carried out as follows: An earthenware vessel a is provided, containing a concentrated solution'of alkaline chlorid or of a chlorid of alkaline earth, in which is placed an anode b, which may consist of platinum or carbon, and cathodes c and d, of iron, mounted in Wooden frames e and f, having parchment -skin g and 7L stretched over them. The earthen vessel is placed in a water-bath lo, heated by a steamcoil t', a stirring device Zkeeping in constant y motion the lead oXid held in suspension in the solution. After the electric current has acted for a time calculated according to the IOO amount of the lead oxid and current intensity used the solution and the finely-divided brown-black dioxid contained in its mass'are drawn o into depositing vessels. The solution that has become clear is returned to the reaction vessel, mixed with litharge, and electrolyzed again. The black-brownmuddy deposit of dioxid is washed several times with Water and is finally dried. The dioxid forms then a black-brown powder in an exceedingly fine state of division.

This process diers, essentially, from the electrolytic oxidation process of lead oxid, which involves the use of a solution of an alkaline sulfate as, electrolyte. This difference is partly one of a pure chemical nature. When sulfates are decomposed electrolytically, alkali is produced at the cathode, while sulfuric acid and oxygen appear at the anode. The sulfuric acid and the alkali combine again to form a sulfate, while the oxygen escapes in the gaseous form. The electrolysis of chlorids and other haloid salts takes place in such a manner that an alkali is likewise produced at the cathode; but the halogen appears at the anode not in the free gaseous form, but as an alkaline salt of a4 halogen oxyacid, such as a hypochlorite. The oxidizing agent of the lead is therefore in the first case oxygen in the nascent state and in the second case a salt of a halogen oxyacid. With the sulfates the oxidation can take place only at the anode, while with the haloid salts, owing to the solubility of the salts of the halogen oxyacid prod uced,the oxidation takes place both at the anode and within the liquid. This chemical combination of the halogen produces a new and most favorable action,whereby a direct storage of the oxidizing agent is effected.

It is obvious that when sulfates are used as electrolyte the oxygen liberated at the anode can only oxidize the molecules of lead oxid that come in contact with the anode. This is indeed what takes place in a quantitative manner at the commencement of the process; but toward the end of the process the particles of lead dioxid formed predominate to such an extent that the nascent oxygen does not meet with a sufficient quantity of lead oxid, so that correspondingquantities of gaseous oxygen escape into the atmosphere. There are therefore losses of current, and if these are to be avoided much less current densities must be used toward the end of the process, which densities must in order to avoid. entire losses be decreased constantly inthe ratio of the lead dioxid produced to the lead oxid remaining. Comparative trials made with sulfates and with chlorids in accordance with the invention have proved this. This oxidation by means of sulfates proceeds best with anode-plates of very large area; otherwise troublesome preparations are neededsuch as inclosing the anode in a paste of lead oxid, sodium sulfate, and magnesium sulfate. As regards the special treatment of lead oxid in sulfate electrolyte this is described in the German Patent No. 109,823, of September 14, 1898, according to which the lead oxid is placed in layers on a horizontal anode-plate at the lower part of the electrolyzing Vessel, so that the oxygen in the nascent state has to penetrate through the thickness of the layer of the lead oxid; but despite all these precautions current losses are unavoidable. The present invention is free from these disadvantages, for whether or not the lead oxid is placed at the anode the oxidation takes place within the liquid. As the oxidizing agent accumulates in the dissolved form the following Aresults are secured by this invention: First, the area of the anode is of no importance; second, all current losses are avoided, for if the current is greater than is required an excess ot' salts of halogen oxyacid is formed, and this excess is utilized for the treatment of the next portion of lead oxid.

The essential difference between the oxidation of lead oxids in the sulfates is that the oxidizing agent cannot be stored in a chemically-bound form, while with the haloid 'salts the oxidizing agent is converted into easily soluble strongly oxidizing combinations, which transform the lead oxid into dioxid within the electrolyte, this storage not causing the least loss of current.

I claim- The herein-described process for the direct conversion of lead oxid into lead dioxid,wl1ich consists in forming an emulsion of the lead oxid with a concentrated solution of an alkali chlorid, subjecting the same to electrolysis, and keeping the emulsion in motion during the electrolyt-ic action.

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

ERWIN QUEDENFELDT.

Witnesses:

JEAN GRUND, FRANZ I-IAssLAcHER.

IOO

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