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CHEMICAL NEWS,}

Jan. 21,

25

VOL. CI., No. 2617.

THE DISCOVERY OF CHLORINE BY SCHEELE. By F. D. CHATTAWAY, F.R.S.

THE elements fluorine, chlorine, bromine, and iodine are usually styled "halogens," their compounds with metals being termed "haloid salts." These names were suggested by Berzelius in his "Text-book of Chemistry" ("Lehrbuch der Chemie," 1843, Fifth Edition, vol. i., p. 266), where he states: "In order to group together by a common name the peculiar class of closely related bodies which give with the metals salts containing no oxygen I shall call them salt-formers,' Corpora halogenia (from "As and yevváw), and the salts yielded by them haloid salts' (from "As and tidos).

Of the four halogens chlorine was first discovered. It was isolated about the year 1774 by Karl Wilhelm Scheele. Scheele was born on December 19th, 1742, at Stralsund, an important town on the Baltic, and the Capital of Pomerania. His short, active life was spent in Sweden, to which country he was taken in early youth, though it is recorded that all his scientific papers were written in German, his native language, and then translated by a friend into Swedish for publication. At the time of the discovery of chlorine he was thirty years of age, and was acting as assistant to an apothecary at Upsala named Lokk (the name is variously spelt in different lives of Scheele as Lokk, Look, Looke, and Loock). He had obtained permission to use the chemical laboratory of the University of Upsala, where Bergman was professor, and it is highly probable that the isolation of chlorine was effected there.

Scheele was engaged in studying the native dioxide of manganese, a mineral known at the time as braunstein, in Swedish Brun-sten, or magnesia nigra. Wishing to ascertain the action upon this substance of all the common acids, he treated it with hydrochloric among others, and thus first prepared chlorine by the method still used in its manufacture. Scheele's original paper appeared in 1774 in the Transactions of the Royal Swedish Academy of Sciences. In section 6 of this paper he describes the action of hydrochloric acid upon manganese dioxide as follows:-"I poured half an ounce of pure spiritus salist upon half an ounce of finely powdered braunstein. This acid after standing for an hour in the cold had become dark brown. I poured part of this solution into a glass vessel, and allowed it to stand open in a warm place. It gave off a smell like warm aqua regis; in a quarter of an hour the smell had gone and the solution become clear and colourless. The rest of the brown solution was digested with a view to see whether the salt acid would become

* Kong Vetenskaps Academiens Handlingar För Ar, Stockholm, 1774, vol. xxxv. "Om Brun-sten eller Magnesia och dess Egenskaper," Sections 1 to 35, pages 89-116; and "Om Brun-sten eller Magnesia nigra och dess Egenskaper," Sections 36 to 45, pages 177194. English translations of these papers are to be found in "The Chemical Essays of Charles William Scheele," translated by Thomas Beddoes, London, 1786, and in No. 13 of the "Alembic Club Reprints," where a translation of a French version is given. A German translation is found in "Sämmtliche Physische und Chemische Werke nach dem Tode des Verfassers Gesammlet und in Deutsche Sprache

herausgegeben," von Dr. Sigismund Friedrich Hermbstädt, Berlin, 1793, vol. ii., pp. 35-90.

Scheele throughout his papers refers to the native manganese dioxide which he used as "Brun-sten"; in the passages quoted the more familiar German term has been used. Scheele uses the alternative name "magnesia nigra" in the title of his second paper. Curiously enough "nigra" is omitted in the title of the first paper. Scheele designates hydrochloric acid indifferently "spiritus salis," "acidum salis," and "salt syra.". In each case the name used

by Scheele has been retained. A note is added later on the names by which hydrochloric acid has been successively known.

saturated with the braunstein. As soon as the mixture effervescence ensued which lasted till the next day, when the acid was found to have become saturated. Upon the undissolved residuum I poured another ounce of spiritus salis, whereupon exactly similar phenomena followed, and the braunstein was almost entirely dissolved, a small quantity of siliceous earth only remaining."

He concludes section 13 with the words " Before I enter upon any explanation of these singular phenomena it will be necessary to point out the general properties of braunstein," and this he proceeds to do in section 14 as follows:

"When braunstein is saturated with phlogiston it loses its black appearance and becomes colourless; the black colour, however, reappears as soon as the phlogiston separated from it again.

"There is no way of producing a colourless solution of braunstein without combining it with phlogiston.

"By means of these four general qualities of braunstein discovered by a series of experiments, all its known effects can easily be explained."

The action of other acids is then described, but nothing further relating to chlorine occurs until the behaviour of the mineral with hydrochloric acid is again and more fully described in sections 23 to 26. At the beginning of section 23, referring to the effects described in section 6, he proceeds: "It does not immediately appear whence braunstein should obtain its phlogiston, nothing combustible being added here and the entire solution taking place without heat." He regards it as showing that spirit of salt contains something combustible--that is some phlogiston. He notes that spirit of salt when digested with braunstein in the cold forms not a colourless but a dark brown liquid, and is thus capable of dissolving it without adding anything, and proceeds :-"Braunstein adheres here so loosely to the salt acid that it may be precipitated by water, the precipitate showing the same properties as the original material. Whenever I exposed the mixture of braunstein and spiritus salis to digestion an effervescence ensued with a smell of aqua regis. In order to set this new discovery in a clear light I took a retort containing a mixture of braunstein and acidum salis, and having tied to its neck an empty bladder I put it into hot sand. An effervescence ensuing the bladder became filled. When the acid no longer occasioned any effervescence, which was a sign of its saturation, I took the bladder off and found that the air produced had rendered it as yellow as aqua fortis would have done. It did not contain any fluid air, but had a very sensible pungent smell, highly oppressive to the lungs, and resembling that of warm aqua regis. The solution remaining in the retort was clear and of a yellowish hue, which was owing to the iron contained in it." The formation of the clear solution is due, according to Scheele's views, to the braunstein having combined with phlogiston, and he adds-" But whence did it acquire its phlogiston? From the acidum salis. The matter of heat has no share here, because the solution hecomes limpid without it if it be only exposed to the air for a few hours. The following is the theory of the solution. The braunstein is first attracted by the salt acid, and thus we have a brown solution. The braunstein when dissolved acquires by means of the acid a strong attraction for phlogiston, and readily withdraws it from the particles of the acid with which it is combined. These particles having thus lost one of their constituent parts, and being but very loosely combined with the phlogisticated braunstein, are expelled from it by the remaining salt acid which has not yet suffered any decomposition, and appear with an effervescence as a highly elastic air. The brown colour has now disappeared

and the solution become clear as water."

Scheele thus regards chlorine as the residue left after phlogiston has been abstracted from the acid obtained from salt, and terms it "dephlogisticated salt acid," stating that whenever it is enabled to combine with phlogiston it assumes its former nature and again becomes true salt acid.

Mix

He next studied the properties of the new gas, and continues as follows:-"In order to investigate the properties of this air it is best to examine it in the elastic state. common salt acid with levigated braunstein in any quantity in a glass retort, which is to be put into warm sand, and attach a glass bottle capable of containing about twelve ounces of water. Into the bottle put about two drachms of water; the joints are only to be luted by tying a piece of blotting paper round the neck of the retort and fixing the bottle upon this. In a quarter of an hour or a little longer a quantity of the elastic fluid going over into the receiver gives the air contained in it a yellow colour, and the receiver is then to be separated from the retort. At this time, if the paper has held fast, a portion of the aërial fluid will rush out with some force. The bottle having then been immediately closed by a previously fitted cork, another one is to be at once fixed to the neck of the retort. Several such vessels may thus be filled with dephlogisticated salt acid. In the process care should be taken to fix the retort in such a position that if any liquid condenses in the neck it may run back. The water put into the bottles serves to condense the vapours of salt acid should any go over. fill several glasses at once in order to get a good quantity, and to avoid the trouble of repeating the process as often as I want some of the fluid for my experiments. It is better to make use of small vessels for receivers, because if one large one is used a good deal of the substance is lost every time the cork is taken out. The bodies which I wished to expose to the action of this dephlogisticated salt acid I hung on a glass tube, which I fastened to the cork." With gas thus prepared Scheele discovered many of the notable properties of chlorine. He observed especially that blue litmus paper, red, yellow, and blue flowers, and green plants lost their colour on exposure to the gas, and that the former colours could not be restored either by alkalis or acids. He noticed further, that all metals were attacked when placed in it, and that when a drop of a 'solution of ammonia was introduced hanging from a glass tube "a white cloud was produced, and a great number of air bubbles were discharged which on bursting yielded a vapour."

Bergman, his friend and contemporary, adopted Scheele's views respecting the process by which the new elastic fluid was formed. He describes braunstein as a substance possessing a great affinity for phlogiston, and able to remove it from salt acid, which thereby becomes dephlogisticated and consequently able to act upon substances containing phlogiston, removing the latter principle from them and being re-converted into salt acid.

I

Compounds containing Iron Peroxide, FeO2.-L. Moeser and H. Borck.-When a mixture of ferric nitrate and strontium nitrate is heated in a current of oxygen, a compound of formula SrO.FeO2 is obtained. Similarly, BaO. FeO2 can be prepared by heating a mixture of barium hydroxide and ferric hydroxide in a current of oxygen. The compounds are both black powdery substances without distinct crystalline form. They are undecomposed when heated to 650°, while at higher temperatures they decompose into Fe2O3, SrO, or BaO and O. With water and with hydrogen peroxide oxygen is evolved. Acids decompose the compounds with liberation of oxygen, and they are characterised by the ease with which they give up oxygen. The FeO2 in the compounds plays the part of an acid oxide.-Berichte, xlii.. No. 16.

RESEARCHES ON THE QUANTITATIVE DETERMINATION OF THE ACID EARTHS.*

By LUDWIG WEISS and MAX LANDECKER. (Concluded from p. 16).

C. Separation of the Acid Earths from One Another. We must first of all describe how the acids were separated by Marignac and Rose's methods.

On

Marignac's Method. The mixture of niobium and tantalum oxide however obtained was dissolved in hydrofluoric acid, to every four parts of oxide in the boiling solution one part of acid potassium fluoride was added, and the liquid was concentrated till I grm. of oxide was contained in 7 cc. of the solution. On cooling, fine needles of potassium tantalum fluoride separate out; they are washed with water till the wash-water does not colour tincture of gallnut orange after standing for two hours, but is precipitated pure sulphur-yellow. From the mother-liquor and the wash water on evaporation more of the salt is obtained, and mixed with it leaflets of niobium salt. further evaporation the niobium salt crystals are obtained. (For preparations re-crystallisation from hydrochloric acid is to be recommended, especially in the case of tantalum). Rose's Method.-Rose melts the purified oxides with boils, after addition of some hydrochloric acid. On cooling potassium fluoride, digests the mass with much water, and from compounds rich in tantalum, a large part of the thirds are evaporated off, it is allowed to stand for twentyThen twopotassium tantalum fluoride crystallises out. four hours in the cold, and thus the rest of the salt is obtained. It is seldom necessary to evaporate the filtrate with sulphuric acid, the residue ignited, washed with a third time. The liquid containing niobium is evaporated water, and again ignited; thus niobium pentoxide containing some titanium is obtained. To determine the titanium, another quantity of the fluoride double salt is dissolved in hydrochloric acid, warmed with zinc in order to reduce the titanium compound, and the amount of it is then determined volumetrically with potassium permanganate. It will at once be seen that neither method provides an accurate quantitative separation.

As working with hydrofluoric acid is unpleasant we tried to discover methods which would enable us to dispense with this acid.

1. Separation Experiments with Oxalic Acid.-Freshly precipitated niobic acid dissolves easily in warm oxalic acid, freshly precipitated tantalic acid less easily, and the difference is still greater if the two acids have been prepared some time previously. Then tantalic acid dissolves much less easily than niobic acid.

If oxalic acid solution is boiled with precipitated niobic acid, the latter never quite dissolves; if the hot liquid is allowed to stand for some time, a clear solution is obtained in one operation when the temperature has fallen to about 60°.

solvent power on tantalic acid to such an extent that only We now tried by diluting the oxalic acid to lower its niobic acid would be dissolved; it was, however, unsuccess

ful, for even one-eightieth normal oxalic acid dissolved appreciable quantities of tantalic acid, and more dilute oxalic acid solution did not dissolve niobic acid well.

2. Acetic Acid and Hydrogen Peroxide.-This method also was not promising. A 2 per cent acetic acid solution containing hydrogen peroxide dissolves almost as much tantalic as niobic acid, and on decreasing the acidity no decrease in the solubility of either of the acids was

observed.

3. Fusion with Ammonium Monosulphate.-The solubility relations on fusing with this salt have already been mentioned. Unfortunately, in this case also it is impossible to effect a quantitative separation, for one part of the

* From the Zeitschrift für Anorganische Chemie, Ixiv., 65.

0.2364 0.2367 0.0912 o'ogog

Nb2O5

Ta205

4. Fusion with Soda and Saltpetre.-When niobic acid is fused with soda and saltpetre, observing the same precautions as with titanium, a white melt is obtained; it dissolves readily in hot water. When carbon dioxide is led into this solution it remains clear even if the action is allowed to continue for hours.

A titanium melt prepared similarly is soluble in hot water with great difficulty, a large amount of crystalline residue remains, and only dissolves on boiling, after the addition of more water.

Thus we have here a way of separating the greater part of the tantalum from the niobium. If carbon dioxide is led into the tantalum solution, after some time a white precipitate is obtained which contains all the tantalum; the supernatant liquid is quite free from tantalum. The method of procedure is as follows:

In order to get a quantitative separation it is essential never to take too much soda, but only enough to obtain the melt in the state of a thin liquid. The amount of saltpetre depends upon the quantity of substance used, but for quantitative analysis is never more than the amount which covers the tip of a knife. Thus there is the additional advantage that only an inappreciable amount of platinum goes into solution in the fusion process.

The saltpetre must never be completely converted into nitrite or the precipitation fails. In this case during the fusion, rapidly solidifying yellow crusts are formed, the whole mass solidifies in a yellow cake of radiating crystals, and is not suitable for a separation.

The melt is dissolved in warm water, so that the crucible lying on its side is just covered with water; it is warmed, and the undissolved sodium tantalate is filtered off, washed with warm sodium bicarbonate solution, dissolved in sulphuric acid containing hydrogen peroxide, and precipitated as Ta(OH), with sulphurous acid.

Into the filtrate, which contains all the niobium as niobate and the rest of the tantalum, a steady current of carbon dioxide is led after it has become quite cold. After exactly fifty minutes the first formation of flakes begins; it increases after some minutes, and is usually finished in half-an-hour. It is then boiled for a short time, and the precipitate is allowed to settle over-night; it then filters easily, and is further treated as above.

This separation depends very much upon the tempera ture at which fusion takes place, the amount of soda used, the amount of water, the temperature of the solution, &c., and it was only after a long time that good results were obtained. Moreover, it has several times happened since that less accurate results were obtained. It is perhaps possible that the addition of ammonia or sodium bicarbonate would give a good result. Carbon dioxide must never be led into the warm solution; in this case only about half the tantalic acid is precipitated.

Used Found

Used

0.1498 Ta205

O'1499 99

This method is very useful for the analysis of tantalites; we are convinced that on a more thorough investigation it will prove surprisingly satisfactory.

After standing for some weeks a solution obtained by fusing niobic or tantalic acid with soda and saltpetre gives small crystals. Those from a niobium solution appeared to the naked eye like small rods, and under the microscope they looked like simple transparent rhombic crystals consisting of a prism bounded on two sides by two domes. The crystals were yellow and very soluble in water; they became colourless when boiled with alcohol, but were not altered by water. Their solution had no effect either upon litmus- or turmeric-paper. After being kept a long time they effloresced and became opaque, but preserved their crystalline form.

The tantalate crystals were also very small, but colourless and hexagonal. They dissolved very easily in hot water, and gave a distinct blue coloration with litmus. Turmeric-paper was strongly affected, being turned brown. Unfortunately, we had not enough of the crystals to investigate them quantitatively; by concentrating the solutions they could not be obtained again, as when evaporation is carried on too long they are decomposed, and precipitates of niobic and tantalic acid are formed.

D. Analysis of Minerals containing the Acid Earths. We give herewith some analyses of tantalites. We had at our disposal tantalites from Australia and America. Qualitative analysis gave for all minerals almost the same constituents, viz., tantalum, niobium, titanium, tin, Silica and manganese, iron, aluminium, and calcium. tungsten could not be detected. (Further investigations are in progress of another constituent present in small quantities).

The quantitative analysis was performed as follows:A weighed quantity of the finely powdered material was added to fused potassium sulphate, and heated until a uniform flux without dark streaks was obtained. After the

The

melt had cooled it was extracted with hot water containing sulphuric acid, and to the boiling solution a moderate amount of sulphurous acid was added-20 to 30 cc. amount of sulphurous acid to be added depends upon the appearance of the precipitate obtained; enough must be added to remove the milky appearance of the precipitate and to cause it to form a flocculent mass.

It is best to keep the liquid with the precipitating Then reagent boiling for about twenty to thirty minutes. all the tin is deposited as metastannic acid with the acid earths. It is then filtered, and the precipitate is washed with hot sulphuric acid containing sulphurous acid until the iron reaction is not obtained, The filtrate, which contains the other elements except tantalum, niobium, titanium, and tin, is treated according to the usual methods of quantitative analysis.

It is best to lead sulphuretted hydrogen into the acid filtrate to make sure whether all the tin is precipitated. If a small tin precipitate is formed it is added to the ammonium sulphide solution obtained later, and then manganese and iron are separated as usual.

The washed acid earth precipitate neutralised with some

dissolve the metastannic acid. As this is converted into

stannic sulphide rather less easily than the other tin compounds, it is best to attach to the funnel a little piece of black rubber and a pinchcock, so that the ammonium sulphide can be allowed to act for some time on the precipitate. Then the liquid is allowed to run off, and the precipitate is washed once more with warm ammonium sulphide. It must not be forgotten that yellow ammonium sulphide must be used to dissolve the metastannic acid, as it is almost insoluble in the colourless sulphide.

The precipitate freed from tin is ignited in a platinum crucible and fused with soda and saltpetre in the way described above, care being taken not to use an excess of soda or saltpetre. It is sufficient to use about double the quantity of soda, and to be very sparing with the saltpetre which is added later.

After dissolving the melt with hot water, the liquid is boiled for some time in order to make sure that all the tintalate has gone into solution. It is then filtered from the insoluble titanium residue, and some drops of the filtrate are tested for titanium with the usual reagent.

If the amount of titanium in the mineral is small (3 to 5 per cent), the filtrate is quite free from it; carbon dioxide can then be at once passed in to precipitate the tantalum, and the liquid treated as described above. If titanium is still present in the filtrate, sulphuretted hydrogen must be passed in, and the precipitate of titanium formed filtered off. Then both titanium precipitates are dissolved in sulphuric acid hydrogen peroxide, the two filtrates are put together, the pertitanate solution is reduced with sulphurous acid, and the titanium precipitated with ammonia.

As carbon dioxide does not precipitate the tantalum from tantalum and niobium solutions containing sodium sulphide and obtained in this way, it is necessary, first, to destroy the sodium sulphide with sulphuric acid, to precipitate the acid earth with ammonia, and to subject the precipitate obtained to fusion once more with soda and saltpetre, dissolving the melt in water, and then leading in carbon dioxide.

This method gives very accurate and concordant results. It has the advantage of rapidly leading to the desired result. The results were as follows:

Thus it must be a mixture of tantalate and metatantalate of manganese. Calcium and titanium, which are present in the ratio of 1: 3, must be present as metapolytitanate :

E. Qualitative Detection of the Acid Farths.

In concluding the account of these researches we will give a summary of the reactions of niobic and tantalic acids, teking into account specially the above results.

1. Reactions of Tantalum.

The statement (e.g., Treadwell, Zeit. Anal. Chemie) that ignited tantalum oxide is not opened up by fusion with fotassium moncsulphate is erroneous. Tantalum oxide is very easily and completely decomposed by fusion with this salt. The melt is quite clear in the liquid state; on boiling with water tantalic acid is separated from the melt but not quantitatively, and in quite a different form from what it was before fusion, for it is easily soluble in the warmth and on addition of hydrogen peroxide.

By fusion with caustic potash tantalum oxide is very easily converted into a clear solution; this melt is completely soluble in hot water.

By fusion with sodium hydroxide it is also converted into the soluble form, but this sodium tantalate is soluble in hot water only when the excess of caustic soda is washed away.