US2173141A - Electrolytic recording paper - Google Patents

Description

Patented Sept. 19, 1939 PATENT OFFICE.

2.173.141 rmcrnonmc nrconnmc. rm

Paul Talmey, New York, N. Y., assignor to Radio Inventions, Inc., New York, N. Y., a corporation oi New York No Drawing. Application July 16,

Serial No. 31,564 8 Claims. (Cl. 204-1) This invention relates to cording paper. Such paper is employed to transform electrical impulses into graphic markings and its use is well known in the art of recording telegraph signals and for the facsimile reproduction at a distance of written, printed and photographic material of various kinds.

The present invention deals principally with such electrochemical paper and with the method of using the same to give rise to such graphic markings. Accordingly it is considered unnecessary to describe the apparatus and devices used at the transmitter to give rise to electrical signals corresponding to the .visual properties of the matter to be transmitted, since such devices are well known in the art and may be of any suitable character.

Receiving devices employing electrochemical paper are likewise well known in the art and accordingly detailed description thereof is considered unnecessary in this specification. A suitable receiving device for the employment of my electrochemical paper may consist of a mecha nism for feeding the paper in one direction at a'suitable speed and means for moving an electrical contact, hereinafter referred to as a. stylus, pressing upon the paper so as to afford electrical contact therewith, along the paper in the other direction.

It is to be understood that the combination of these two motions just referred to is identical electrochemical rewith or substantially equivalent to the process; usually referred to as scanning and accomplishes the substantially complete coverage of all points lying in a given area of the paper, in synchronism with a similar operation simultaneously performed at the transmitter. It is also to be understood that the relative motion of the paper and the stylus may be secured in a fashion other than above described. ,For example, the stylus may be stationary and the paper put in motion relative to the stylus. Likewise any other suitable receiving device capable of use with electrochemical paper may be employed in practicing my invention.

In receiving devices suitable for use with my electrochemical paper the electrical contact, other than the stylus, may conveniently take the form of a metallic surface, hereinafter referred to as platen, in contact with the surface of the paper other than the surface on which the stylus presses. Suitable devices maintaining the necessary pressure exerted upon the paper by the stylus and the platen in order efliciently to make contact therewith arewell for regulating and known'in the art of electrochemical recording and therefore not herein described.

Electrochemical recording, as previously practiced, has entailed many serious disadvantages which have virtually precluded its use, except 5 under the supervision of persons skilled in the art, and accordingly the use of such recorders in connection with domestic receiving devices has been practically impossible.

Among other disadvantages of electrochemical processes as previously employed have been the necessity of using a chemical solution or at least a liquid bath or its equivalent, arranged to moisten the recording paper just prior to its passage through the receiving device, and the practical impossibility of providing a suitable receiver in which such chemical solution or bath could be maintained without the necessity of skilled supervision. Another difliculty with previous electrochemical papers has been the poisonous or corrosive nature of the chemicals used therein, precluding their use in domestic receiving devices.

Still another difficulty encountered in the electrochemical paper hitherto employed has been the virtual impossibility of securing a substan- 25 tially black mark upon a substantially white background, without the use of some expensive chemical such as a silver salt, or without the use of photographic processes which are impracticably complicated for domestic use. 30

In the employment of electrochemical recording papers there also has been great difficulty encountered by the occurrence of a phenomenon commonly referred to n the art as dragging. .This refers to the fact that when current giving rise to the signal marking ceases, there has been a tendency for the stylus to carry along in a mechanical fashion certain marking materials such'as those which have been electrochemically produced by the signal.

This has caused the reproduced graphic markings to be unduly elongated in comparison with the original markings at the transmitter. Numerous remedies for this fault have been proposed, including, an abrupt reversal of the elec- 45 tric current at the instant when the signal current ceased, but such remedies have been complicated and costly, as well as ineffective in most the electric 35 v erly located as the end thereof was gradually con-- sumed, and to keep the stylus pressing upon the paper to the proper degree.

Yet another fault of electrochemical ,papers hitherto used has been the impermanency, both of the paper itself and of the record produced thereupon. The impermanency of the paper prior to its use has been a feature especially harmful with respect to the possibility of preparing such paper on a commercial scale and distributing it to domestic consumers through ordinary channels of trade, such distribution may cause deterioration in such paper, making it unfit for later use.

One purpose of my invention is to provide an electrochemical paper and amethod of electrically recording graphic signals thereupon, which can be utilized without the necessity of employing chemical solutions or other means to moisten the paper just prior to its use.

Another purpose of my invention is to provide an electrochemical recording paper which shall be substantially white in appearance and so to employ the same that the signal markings produced thereupon shall'be substantially black in color. Such black and white reproductions are much more desirable in the majority of cases than the vari-colored markings which have been produced by previous I electrochemical recording processes and the colored backgrounds afforded by many previously used-papers, especially those using iodine compounds as marking chemicals.

Still another purpose of this invention is to provide an electrochemical paper which shall be non-poisonous and non-corrosive in character, so as to be suitable for domestic use.

Still another purpose of my invention is to provide an electrochemical paper which may be stored over long periods of time before its actual use without substantial deterioration in its recording efficiency.

Another purpose is to provide an electrochemical paper which shall remain unaltered in appearance over long periods of time after markings have been recorded thereupon, so that a substantially permanent record may be obtained from receiving devices employing such paper.

Yet another purpose of this invention is to provide an electrochemical paper which may readily be prepared in relatively large quantities from materials easily and cheaply obtained.

Another purpose of this invention is to provide an electrochemical paper in which the signal marking produced by a stylus functioning as an electrode, will cease substantially instantaneously upon the cessation of the signal current, so that dragging is substantially absent and accuracy of reproduction thereby greatly facilitated.

Another object of my invention is to provide an electrochemical paper having incorporated therein an ancillary sensitizing material which will greatly increase the graphic response of the paper for current of a given signal strength, thus allowing the use of smaller and more economical electrical apparatus at a domestic receiver.

Another object of my invention is to produce an electrochemical paper having incorporated therein a substantially insoluble chemical com pound for marking purposes, which insoluble compound may conveniently be formed in situ by the decomposition of a soluble compound with which the paper has previously been impregnated.

A further object of this invention is to provide an electrochemical paper and a method Oi.- us ng since the time delay inherent in the same,"which will not effect any appreciable chemical-alteration of the stylus material. therebyavoiding the need of continuously feeding the stylus during operation of a receiver and thus facilitating' the maintenance of uniform optimum pressure between the stylus and the paper.

The following specification and description of my electrochemical paper and the method of using it is considered a discl are fully adequate to enable one skilled in the art to reproduce the same and accordingly it is thought that drawings neither are necessary nor would they be of any assistance in furthering such disclosure.

At this point it is thought to be of assistance in a full understanding of my invention, that certain terms and phrases hereinafter employed be defined as to the exact sense in whichthey are used. By the phrase incorporation of a material in a paper I refer to such material being applied to the paper by mixing with the paper pulp during the process of manufacture, by being physically or chemically caused to adhere to the surface of the paper, by being impregnated more or less thoroughly into the pores of the paper or by being caused chemically or physically to combine with the paper in any fashion which will provide a suitable milieu for-the electrochemical processes which are used to cause graphic markings upon the paper.

In defining and referring to the chemical elements employed in my invention, a convenient and precise mode of reference is to indicate their position in that arrangement of elements commonly referred to as Mendelyeev's Periodic Table. Since such tables as published frequently employ different designations for the respective vertical and horizontal groupings, I find it desirable to avoid possible ambiguity by referring at all times to the specific table given in the Hand Book of Chemistry and Physics, 15th edition, published by the Chemical Rubber Publishing Company of Cleveland, Ohio, as a standard reference work, well known in the art. The other chemical terms employed in this specification are thought to be sufficiently well known in the art so that specific definition thereof is unnecessary, and such terms are to be interpreted according to their customary meanings in the electrochemical art, unless otherwise specifically defined at the time of their use herein.

A brief discussion at this point of the general types of electrochemical recording papers, together with a statement of certain advantages and disadvantages of the various types is thought to be helpful in a better understanding of my invention.

In electrochemical recording, it is possible to divide the processes used according to whether substantially the entire marking effect is produced by materials associated with the paper itself or whether the electrodes used to carry the current'into the paper are themselves acted upon in such fashion as to contribute to the marking eil'ect produced by the current.

In processes of the last mentioned type, it is possible for either the stylus or the platen to take part in the chemical reactions. but owing to the fact that such reactions entered into by the electrodes cause a gradual using up of the electrode material, it has been customary to make the stylus alone the electrode which is thus used up. In this manner the stylus may be gradually fed forward as it is consumed, this type of compensation for wearing down being a more practical one than feeding of the platen.

and also allowing better definition to be obtainedin the reproduced material.

In recording processes of the type where the electrodes are consumed, it is possible for the stylus to be connected to function either as an anode or as a cathode.

feeding just mentioned.

Likewise the first type of recording process above mentioned, where the electrodes act merely as substantially passive current conducting devices and substantially are not consumed durthe marking process, may also be divided into two sub-types, ,namely where the stylus functionsrespectively as an anode or'as a cathas many other such substances which are com-' mon in our larger cities, due to smoke and industrial activity. This oxidizing atmosphere is nal sufiicient to duplicate the action of the atmosphere is low, then there is the equivalent of a high chemical background of noise. Now highly sensitive papers 'of this type must have a low signal to chemical background ratio, and hence, instability. For these reasons, for oxidizing reactions there should be selected a paper relatively insensitive.

When the stylus functions as a cathode on the other hand, the chemical reactions occurring thereat will in general be of a reducing nature. Since the atmosphere rarely contains reducing substances, one can in general use a more sensi tive paper, since it can be said that the chemical noise level of the atmosphere in a reducing direction is much lower than it is in an oxidizing direction.

Certain chemicals which give rise to marks by a reducing action, such as silver salts, frequently have been proposed for electrolytic recording purposes. Such salts, however, are characterized not only by their relatively high cost, but also by their great tendency to be reduced when exposed to light.

I have discovered that the polyvalent elements are better suited to enter into such reducing reactions, for purposes of electrochemical recording, than are monovalent or even divalent elements in general. More specifically, I have diselements of the odd series of Group V, particularly those of a metallic or metalloid character, are especially suited for electrochemical recording by means of a reducing action taking place at-the recording stylus. v

As previously mentioned, the electrical recording proceses of the prior art have encountered practical difliculties in securing a cessation of mark produced by the stylu's,.at the exact moment when the marking current signal ceased. I have discovered that to a very conslderable degree this dragging effect may be attributed to the use of a. soluble chemical comsecure great improvement, tical elimination of dragging.

ue to the various improvements and novel suitable for domestic use by persons unskilled in the art.

For a clear understanding of the details of my invention rent, with a minimum of power consumption from the signal receiving apparatus. Additionally to these two compounds just referred to I have found it desirable to incorporate certain other vmaterials, which enter more or However, its general operation may be later point of this specification, where their modi operandi may more clearly be disclosed.

I have found that of the elements in group V antimony is particularly suitable, although hismuth or arsenic may also be employed. Since I tion.

It is well known to those skilled in the chemical art that bismuth and arsenic give rise to electrochemical reactions of a nature similar to those of antimony and any necessary slight differences in the processes of producing paper for using these two elements in place of antimony may readily be ascertained from the existing chemical art and will be apparent to persons skilled therein. For example, I have made satisfactory recording paper by impregnation with BiCla following the identical process hereinafter described for the use of SbCh.

A large number of compounds of arsenic, antimony and bismuth have been tried and found in every case to be operative in the practice of my invention. However I have found that certain compounds of the elements just mentioned have influences upon the reduced metal produced by the electrolysis thereof, or the indirectreduction thereof in accordance with the operation of marking according to my invention, influences which tend to destroy the distinctive marking accomplished by the reduction of the metal. All such distinctive effects, whatever their nature, may be grouped under the general term of fading cflects, and probably are due to a re-solvent action exerted upon the reduced metal by certain materials either present originally in the paper or produced therein by the electrolytic reactions.

With certain compounds, especially with that known as pyro potassium antimonate, I have found this fading action to be so very rapid as to ap-- preach in speed the rate of formation of the metal itself. Manifestly, while such compoimd satisfies the terms of my invention, and will produce markings, the markings will be so fleeting in character as to render the use of such compound under usual circumstances undesirable, However it may be desirable in some cases to produce markings of a fugitive character, and I have found that by suitably adjusting the quantity of a compound producing stable markings relative to the quantity of a compound of a fading character such as the one just mentioned, in preparing a paper according to my invention, it is possible to produce recording paper bearing the mixture of the two compounds, which paper upon electrolysis will produce markingswhich will fade out (after their appearance) at practically any desired rate of speed.

For general use however, where permanence of record is desired I have found that certain halogen compounds of antimony are especially suitable for use in practicing my invention, although oxids or other compounds of antimony are also very eflicient as chemical compounds for use in recording papers.

As an illustration of one mode of practicing my invention, I shall now describe the production of an electrochemical paper carrying antimony oxychlorid together with potassium chlorid and gelatin. The usefulness of the gelatin in practicing my recording method will be hereinafter described in detail and at this point it is sumclent to state that I have found it to be of utility and to describe one method of incorporating it in a paper.

The gxychlorid of antimony is a white, substantially insoluble and permanent material. While I employ the term oxychlorid of antimony, it is to be understood that antimony forms a number of oxychlorids, at least four of which are described in chemical literature. There is available on the market a material known commercially as antimony oxychlorid or Powder of Algaroth. This material consists usually of a mixture of several oxychlorids and sometimes oxids of antimony and while I have found it possible to employ this material directly in the production of my paper, yet I prefer to form directly in the paper an oiwchlorid of antimony which I have found most suitable for use with my invention.

If a concentrated solution of antimony trichlorid in any suitable medium such as water, an aqueous solution of hydrochloric acid, carbon disulfid or alcohol is first made up, it. is then possible to impregnate with such solution the recording paper and so to treat the paper as to change the antimony trichlorid into antimony oxychlorid or antimony oxld, such change taking place within thepores of the paper itself.

As an alternative method to the one just described, the antimony oxychlorid may be produced as such in a suitable vessel exterior to the .paper, and then, after suitable treatment, as hereinafter described, be associated with the paper as by any suitable physical or chemical binding means, or by incorporation with the relations of systems dried by filtering under pressure.

paper pulp during the manufacture of the paper.

The last mentioned method of producing the oxychlorid exteriorly to the paper may conveniently be practiced in the following fashion. In spite'of the theoretical complexity of the phase containing antimony compounds, the oxychlorids are easily formed. If a 'solutionof antimony trichlorid in water is placed in thebottom of a large tube and water is added in a quantity which may be about fifty times the weight of the trichlorid present, while the temperature is held constant at around room temperature, a flocculent' white precipitate (SbiOsCh) will settle to the bottom, usually in less than one halfhour. I

The water can then be decanted or drawn of! above the precipitate and the precipitate further not to dry the oxychlorid completely, as its flocculent nature is soon lost in the drying. A thick paste is the best condition to retain this characteristic. Such paste may then be spread upon the paper, forced into its pores or incorporated therein during the paper manufacture.

The method of preparation to'gether with the paper pulp oifers a method quite suitable for use in connection with ordinary paper manufacture. The oxychlorid can be prepared with ease in quantity with suitable equipment. It is possible toadd it dlrectly to the beater in manufacturing the paper or at any other suitable point.

The oxychlorid may also be prepared by adding SbCh directly to the pulp in a tank and then beating thoroughly. Since the pulp is 90% water, the dilution ratio will be sufficient to form Sb4O5Clz satisfactorily. If necessary, a small quantity of Ca.(OH)2 may be added to neutralize the excess acid. I

The paper thus produced with antimony oxychlorid incorporated therein may then conveniently be treated with a bath containing gelatin and KCl in order that these latter materials may be present to play their respective roles during the marking process.

The relative proportions of antimony trlchlorid, its solvent and the water used for precipitating the oxychlorid therefrom are subject to possible wide divergence of value, within limits which are well known in the chemical art. For example, the SbCls may be put in contact with hydrochloric acid of three normal strength until a saturated solution is obtained, the mixture being shaken to facilitate the rapid reaching of this condition. Alternatively a stronger solution may be obtained by substituting water for the 3 N acid just mentioned. While I have found that a solution with a specific gravity somewhat greater than 2.0, for example 2.12, seems to be the most desirable, yet it is possible to secure useful results with solutions of specific gravity 1.35 or somewhat lower and my invention is therefore not limited to any special strength of solution.

Assuming that the SbCla solution has been prepared, one convenient method of forming the oxychlorid in situ is as follows:

The paper is dipped in the bath of SbCla and removed when it has absorbed a sufiicient amount of the liquid. I have found that this absorption usually is accomplished within a few seconds, not exceeding 30 at the most, but the time required will depend, inter alia, upon the porosity and thickness of the paper, as well as the temperature of the solution. Too prolonged immersion, for example exceeding 30 seconds, will tend to It is preferred destroy the paper itself. A suitable temperature for this operation is 20 C.

The paper impregnated with the SbCl: solution may then have the excess solution removed from its surface by blotting, pressing, felting or other convenient means and then may be agitated in a bath containing a large quantity of water only, for several minutes. This may be done at approximately room temperature. When the paper comes in contact with the water, the trichlorid is changed toone or more oxychlorids. While I do not limit my invention to the employment of any particular oxychlorid, as previously mentioned in connection with the use of the commercial Powder of Algaroth, yet I believe that the process just described tends to produce a maximum amount of the particular oxychlorid represented by the formula Sb40sCl2 and thoroughly to remove the excess HCl formed. Those skilled in the art can readily vary these conditions of manufacture according to the well known principles of physical chemistry including the so-called phase rule, according to the particular results desired.

Continuing now with the process of preparing the paper, the excess oxychlorid may be brushed off or removed by any suitable mechanical means from the surface of the paper and I have found it desirable likewise to again blot or felt the paper in order to remove any excess of water. The elliciency of this process of impregnation has been found to be a maximum when too great an excess of oxychlorid and water is not present at this point.

The paper may next conveniently be immersed in a solution of gelatin and potassium chlorid. at a temperature of about 140 to 150? F. This bath may be made up in the proportion of 3 grams gelatin, 20 grams KCl and water sufficlent to make 100 c. c. I have found it diflicult to prevent this mixed bath from being depleted by the selective action of the oxychlorid for the gelatin, whereby the former absorbs gelatin and water at unequal rates. With a solution prepared with the proportions above given and kept at approximately the temperatures above stated, this selective absorptive action may be minimized, provided that the paper be previously well washed, sufliciently dried and that it be of a grade suitable for the process, as will be evident to those skilled in the art of paper treatment. For example I have found that ordinary 16 pound bond paper is suitable for treatment substantially as above described.-

Referring now to the KGl and its action in my recording process, the following explanation seems a logical and satisfactory one, but is given merely as an illustration and not as a limitation upon my invention. The KCl is soluble in the water present in my paper and the solution thus formed is an electrolyte of excellent conductivity. The comparatively insoluble antimony compound can directly carry only a small percentage of the signal current, since the ions present are derived chiefly from the K01.

It will be noted that there are two theoretically possible intermediate products produced at the surface of the cathode stylus by the decomposition of the K01; i; e., elementary potassium and nascent hydrogen.

In order to permit one or both of these elements to exist in their reactive form long enough eiiiciehtly to act upon the insoluble oxychlorid. I may insert an auxiliary retaining agent. The adsorptive properties of colloids are well known.

Gelatin or starch are convenient substances and degree of concentration I have found them preferable. The reactive elements probably are adsorbed by the colloidal gelatin or starch, and gradually released to act upon the antimony compound. This action occurs for only an extremely short space of time, but it appears to continue considerably longer than a decomposition without the presence of gelatin 0r starch.

While not confining myself to this particular theory .of operation yet I have determined experimentally that the presence of a colloid such as gelatin or starch in anappropriate form actually does very greatly increase the effective efliciency of my recording paper and process.

In the foregoing description KCl has been mentioned as one example of a suitable electrolyte. One reason why this has been chosen is that its conductivity is extremely high for a given weight thereof and another reason is that in solutions made up with KCl as the percentage concentration is increased, the conductivity substantially increases and reaches a maximum at a substantially saturated concentration.

When the solution is in the paper and the paper progressively dries, the quantity of solution between the electrodes decreases, and naturally the concentration of the solution increases.

The former effect tends to decrease the con-.

ductivity and the latter to increase the conductivity, with the net result that the conductivity of the paper remains substantially constant between useful limits of moisture content.

This particular property of effective resistive constancy does not by any means occur with all electrolytes nor even with chlorids of elements similar to potassium. For example, common salt, NaCl, does not possess this constancy to a degree at all approaching that of KCl, while CaCl: possesses the undesirable property that its optimum conductivityexists at and it increases sharply in resistance when the concentration departs materially from this particular value. It can readily be seen that a desirable recording paper should function with the greatest possible degree of uniformity over a wide range of values of its moisturecontent and the use of KCl tends to accomplish this desirable result, but I do not confine myself to the use of any particular electrolyte, as my invention is operable with any good electrolyte not otherwise deleteriously affecting the reactions involved therein.

In order further to prevent my paper from becoming so dry as to attain an undesirably high electrical resistance, I have found that small quantities of CaCla may be combined with the KCl, in order to take advantage of the well known hygroscopic characteristics of the CaCla, but for the reasons just pointed out it is undesirable to employ a large amount of CaClz because of its undesirable concentration-conductivity characteristic.

I have also found that the gelatin employed in sensitizing my paper seems to act as a lubricant for the stylus during its passage over-the surface of the paper. I have also found that the advantage of a comparatively small quantity of soap, such as potassium oleate, aids the process of electrolytic recording, apparently by decreasing the surface tension and thus affording better contact between the stylus and the paper. Such soap also may act as a lubricant. but I have found it preferable to employ quantities less than one per cent (1%), for example 0.1% has given good results. It has also been found that glycerin may be employed in small quantitles as a hygroscopic agent and likewise as a possible lubricant. I have found it undesirable however to use more than approximately two per cent (2%) as a maximum quantity of glycerin since the presence of glycerin tends greatly to increase the minimum percentage concentration of electrolyte which will afford sufllciently low resistance to give satisfactory. electrolytic action.

While not confining myself to any particular stylus and platen material, yet it will be evident from the principles above outlined that the materials employed for these electrodes should preferably be materials which are attacked to an inappreciable degree, if at all, by the decomposition products appearing at their respective surfaces when signals are being recorded. While it will be apparent to those skilled in the art that metals of Group VIII, especially series 6 and 10, possess the required characteristics and while I have found especially that rhodium for the stylus and palladium for the platen operate excellently, yet these same elements are also characterized by their relatively high cost. Accordingly I have found it possible to substitute other less expensive materials such as tungsten for my stylus, for which latter purpose the great hardness and wearing power of tungsten cause it to be especially suitable, and for the platen I may use even metals such as zinc, which may be slowly acted upon, provided that their reaction products are white or colorless and not detrimental to the desired marks.

It will be apparent that active stylus materials may be employed if so desired, which active materials may enter into the electrolytic reactions and may if desired give rise to special effects such as the production of colored markings instead of the substantially black marking produced by my antimony paper per se.

The marks produced by m recording process are probably due to the reducing action of either the potassium or the nascent hydrogen, or both, produced at the stylus electrode upon my insoluble antimony compound. Such reducing action probably liberates metallic antimony as a final result. However, it is to be noted that the antimony thus liberated does not appear as a deposit upon either of my electrodes, as would probably occur if a soluble antimony salt were employed, but such metallic antimony appears where it is most desired, namely on the surface of the paper itself, adjacent the stylus. However the above theory of operation is merely given as one possible explanation of observed effects and is in no wise to be construed as limiting my invention to such theoretical considerations.

I have found evidence that even in the case of paper prepared in accordance with the disclosure of the first portion of this specification, i. e., with the use of antimony'oxychlorid, there is a slight tendency for the record to fade out, which tendency so to do may be reduced to a minimum by the use of a paper which will have a free acidity not exceeding a small degree.

In general the compounds of bismuth may be employed in a fashion similar to those of antimony, and will reduce readily, for the most part, even in a neutral milieu. Bismuth displays a tendency to spread uponthe recording paper, especially if the speed of the stylus is very low.

This seems to be the result of the metal first reduced continuing to act as an extension of the original cathodic surface of the stylus. While a similar effect exists in the case of antimony, it

does not seem to be as marked as with bismuth, and with arsenic this effect is very slight. The three elements thus act in accordance with their well known gradation of chemical characteristics, especially with regard to their metalloicl 5 character.

I have found that the re-solvent action of certain compounds upon metallic antimony diminishes somewhat in proportion to the length of time elapsing after the formation of the same, and one possible explanation of this fact, is that the antimony is first formed in an amorphous condition which is more soluble than the crystalline formed, and then that the first formed amorphous metal changes with comparative rapidity to the crystalline form. In the finely divided state in which the metal exists as a result of the reducing reactions of my recording process, the marks would appear dark in either' form. Due to the well known instability of the amorphous form of antimony, it is probable that it could exist in that form for only a very short length of time, but would be more readily soluble while in that form. However the foregoing is merely a theoretical explanation of observed facts, and my invention is in no wise predicated upon the correctness of this theory.

Another theoretical consideration which will allow the most suitable compounds to be chosen for the practice of my invention, and which is 1 borne out by electrochemical indicia obtained in practice, is that the best results will be obtained, caeteris paribus, when the non-metallic portion of the compound chosen can exert a depolarizing action upon the marking stylus, whose polarization readily can be estimated by a measurement of the current flowing in the marking circuit.

It is to be understood that, while I have used the term paper in the foregoing specification, my marking compounds and process are equally applicable to fabrics or any material of the same general nature, which may be suitable for use in electrolytic recording processes. By insoluble as used herein is meant aqueously insoluble at room temperature in accordance with the accepted use of the unmodified term.

It is also to be understood that the specific materials and process steps described in the foregoing specification are merely illustrative and not limiting and that my invention is to be limited only by the scope of the claims hereunto appended.

I claim:

1. An electrolytic recording material including a supporting sheet containing in combination a substantially insoluble oxyhalid of an element chosen from the group consisting of antimony and bismuth, and also containing a solution of an electrically conductive compound, in quantity large enough to render said sheet conductive.

2. A supporting sheet for electrochemical recording, containing a substantially insoluble oxyhalid of antimony, a substantial amount of a solution of an electrolyte, a colloidal binder, and also water sufiicient to dissolve said electrolyte to form said solution, said substances interacting upon electrolytic decomposition of the electrolyte to give a dark mark on said sheet.

3. An electrically conductive supporting sheet for electrolytic recording containing a substantially insoluble oxyhalid of antimony, gelatine, and a solution of an electrolyte for making said sheet electrically conductive to a degree whereby substantial electrolysis thereof is possible.

4. An electrolytic recording sheet incorporat- 16 f ing material,

ing therein substantially insoluble oxyhalids of antimony including a substantial vamount stoichiometrically equivalent to the formula SbeOsCh, a water-soluble to combine with sumcient water to combine with said electrolyte and render said sheet substantially electro-conductive.

15 6. A sheet according to claim 4 and also cartying gelatine cooperating with the antim compound to give improved electrolytic recor I 7. A recording material comprising in combination, a supporting sheet. a substantially insoluble oxyhalid of antimony, a water-soluble electrolyte, and suflicient water to combine with said electrolyte and render said sheet substantially electro-conductive.

8. A recording sheet ly insoluble oxyhalid of bismuth, and an ancillary solution oi an electrolyzable compound containing sufllcient water for the ready electrolysis thereof.

PAUL TALIEY;

containing a substantial