I N S T A S T A S E O U S CHEMICAL R E A C T I O N S A S D THE T H E O R Y 0F E LE C T RO LY T I C D I SS0‘21-1T IO N BY LOUIS KXHLESBERG
In a previous article on the theory of electrolytic dissociation,‘ I have briefly discussed the fact that the chemical reactiveness of electrolytes has been urged as a support of that hj.pothesis. In view of the wide-spread idea that instantaneous chemical action, if not all chemical action, is dependent upon ions, the products of so-called electrolytic dissociation, I concluded to subject this question to further experimental investigation. T h e question that I sought to answer primarily was, Can instantaneous chemical reactions causing precipitation by double decomposition (comparable, for instance, with the precipitation of silver chloride in aqueous solutions according to the equation, AgNO, HC1 = -1gC1 -~H?;03) take place in solutions that are exccllctit i~zsulntorsr’ T o investigate this question, 11) drocarbons were naturally chosen as the best solvents known for the purpose in hand. Benzene was used as the solvent, though a few preliminary experiments indicated that petroleum ether, or toluene would have served equally well. T h e benzene used was of the very best crystallizable, thiophene-free variety of Kahlbaum’s manufacture. T h e benzene \vas allowed to stand for days over phosphorus pentoxide, after which it was redistilled from this dehydrating reagent. I t was finally kept standing over metallic sodium. T h e electrical conductivity of this benzene was then tested. A s it is impossible to estimate by means of the Kolilrausch method the electrical conductivity of stibstances of such enormous resistance, another plan was adopted, I t was briefly as follows : n’hat was practically an Xrrhenius resistance cell with the plates less than a niillimeter apart, was Bull. Uiiiv. Wis (1901).
, Science Series, 2,
297 : also Jour. Phys. Clieni. 5 , 339
2
Louis Kn/zZ~726er~7
placed in circuit mith a sensitive galvanoineter and a direct current dynamo, generating a pressure of I I O volts. T h e dynamo was a large machine used to furnish light and power ; and besides the resistance in the cell above mentioned, there was no resistance in the circuit, except the low resistance of the galvanometer and the necessary connecting copper wires. Before using, the cell was in each case dried by heating, as were all containing vessels used in these experiments. TTlien the cell contained air, only a slight movement of the galvanoineter needle could be noted on closing the circuit. O n placing the benzene in the cell and closing the circuit, the deflection of the galvanometer needle was somewhat less than when the cell simply contained air. T h e benzene then condncted less than air. T h i s experiment was repeated at various times with always the same result. In view of the facts found, I did not consider it necessary for in)- purpose to attempt to measure exactly the specific conductivity of the benzene.' I n seeking suitable solutes to be used in benzene some difficulties were experienced ; these need not be recounted here, as they were mainly due to the fact that most salts of metals are practicallj. insoluble in hydrocarbons. I t was finally found, however, that certain oleates of the heavy metals, namely those of coppe:., iron, and manganese are sojuble in hydrocarbons, a fact discovered by Schon.* It might be added at once that the oleates of cobalt and nickel are also soluble in benzene and petroleum ether. I could not find the latter salts described in the literature, a i d hence coiiclnded that they have probably not been prepared heretofore. In this investigation tlie oleates of copper, nickel, and cobalt were used. These salts were prepared -in idea of tlie sensitiveness of the method eniployed may he obtained from the following : With twelve large storage batteries ( i . e.. a pressure of 24 volts) instead of the dynamo, and pyridine of specific conductivity of less than 10-7 reciprocal olitris in the cell a deflection of thirty scale divisions was noted. b'ith a pressure of 110 volts and air in the cell. a deflection of about one-half of a scale division was observed : when benzene was placed in the cell, the deflection was scarcely more than a third of a division. Liebig's .innalen, 244, 266 (18SS).
by heating pure oleic acid with the calculated quantity of standard solution of sodium hydroxide (prepared from metallic sodiiiiii), and then adding to the sodium oleate solution thus formed, a slight excess of the sulphate of the heavy metal, the oleate of which was desired. T h e precipitations were made at rooin temperature. T h e precipitate was in each case thoroughly washed with water and finally carefnlly dried in an oven at I I O degrees. T h e general cliaracteristics of the oleates of copper. iron, and manganese are given by Schoii. T h e oleate of nickel is a green, amorphous, resinous solid at ordinary temperatures. Cobalt oleate is also an amorphous, resinous solid ; it has a dark red color, which turns broitn when the salt is heated above I 2 0 ' ) probably because of decomposition. After the oleates of copper, nickel and cobalt were prepared and dried as above desrribed, they were analyzed by careful ignition in a crucible and subsequent reduction with hydrogen. Tlie results obtained were as follows : 3.3315 g copper oleate yielded 0.3337 g Cn, or 10.02 percent Cu ; for Cu( CI,HqqC32)Z the theory requires 10.16 percent. 5.5671g nickel oleate yielded 0.5240g nickel, or 9.41 pertheory requires 9.46 percent. cent Si ; for Xi(Cr8H330Z)Z 3.9200 g cobalt oleate yielded 0.3834 g Co, or 9.77 percent ; for Co(CIBH3j02)2 theory requires 9.51 percent. T h e oleates of copper, nickel and cobalt are readily soluble in benzene even at room temperatures. T h e solution of the copper salt is greenish blue : that of the nickel salt is green ; and that of the cobalt salt is dark red. T h e colors of these solutions are then similar to the colors of salts of the corresponding metals in aqueous solutions. 011 heating the dark red solution of' cobalt oleate in toluene, the solution turns blue, and on cooling, it again becomes dark red ; this behavior is then exactly like that of cobaltous salts in aqueous solutioiis. When the electrical conductivity of these solutions was tested bj. the rigorous method above described, it was found that they do not conduct better than pure benzene. T h e solutions thus tested were about five percent strong. AI etallic sodium does not precipitate the heavy 35
metals from the solutions of these oleates in benzene ; indeed the solutions were allowed to stand over metallic sodium so as to insure their thoroughly anhydrous condition. A copper oleate solution was allowed to stand over metallic sodium for weeks, without the least change taking place. This was shown by the fact that no copper appeared on the S O ~ ~ U I I and I, that when the sodium was taken ont of the solution, washed carefully with benzene and dissolved in water, not a trace of copper sulphide could be detected on saturating the carefully neutralized solution with hydrogen sulphide. I wish i n this connection to call particular attention to the well-known fact that a freshly cut surface of metallic sodium gradually turns pinkish in color even when kept under a thoroughly dehydrated hydrocarbon, - benzene or petroleum ether, for instance. In performing the experiment of placing metallic sodium in a solution of dry copper oleate in dry benzene the slight pinkish hue that the freshly cut surfaces of the metal assume after a time, must not be mistaken for copper. RIagnesiuin, aluminum and zinc have been kept in a copper oleate solution for weeks without in the least changing their appearance and luster. I t is abundantly proved then by physical and chemical tests, that these oleates in benzene are not electrolytically dissociated. I n the case of the oleate of copper, I made molecular weight determinations in benzene by the cryoscopic method ; the results are given in Table I. TABLE I. ~-
Copper oleate ~-
~
0.6788 1.3805
1
Benzene _
~
1
_
_
13.54 18.45
I ~
. I
Lowering _
.
_
0.107
0.152
1 I
Mol. wt -
2312
2163
Rlr. n’alter D. Patton made boiling-point determications of solutions of copper oleate in benzene. His results are given in Table 11. If a little water is added to the solution, the sodium is acted upon with evolution of hydrogen and becomes coated with a slimy precipitate, probably consisting of a little sodium oleate (which is practically insoluble in benzene) and hydroxide of the heavy metal.
-
Copper oleate _-
0.5551
Benzene -~
11.52
0.050
2563
I Conipare in this connection the interesting observations of M. Gomberg (.lmer. Chem. Jour. 25, j z q (1901))atid those of other observers to whom he ref'ers.
6
Louis Knhlez berg
scrap of platinum under the solution, hydrogen was very copioiisl! evolved, almost entirely on the platinum.' I t is well-kno\.r-n that in the last-named experinleiit the solution of the zinc is accoiiipaiiied by a current of electricity through the metals and the solution, an? that the chemical action is much more vigoroils in consequence. On the other hand it is clear that zinc decoinposes dry hydrochloric acid in dry benzene, and this apparentlj. goes on without a concomitant electric current ; for a piece of platinuin in contact with the zinc does not affect the evolution of lijdrogen in the benzene solution, as it does in the aqueous solution. ,Again, contact with platinum or other metals does not cause inagnesinm to be acted upon by the hydrochloric acid solution in benzene. Iron, nickel, cobalt, copper and cadinium are not attacked by a solution of hydrochloric acid in benzene ; tin and aluminum are slightly acted upon ; lead very slightly. Mercury, silver and, of course, gold and platiiiuni are not acted upon. These statements hold, whether the metals are in the solution by theinselves or in contact with other metals ; in fact no visible effect was caused by contact with other metals. Vetallic sodium is fairly rapidly acted upon by the benzene solution of hydrochloric acid. T h e chlorides of the metals acted upon are practically insoluble in benzene ; they appear on the metals as a white coating after the action has gone on for a sufficient length of time. T h e coating around the sodium had a milky gelatinous appearance after the action had gone on for twelve hours. A perfectly bright globule of the metal remained unchanged after being thus coated over. I wish to state emphatically in this connection, that in obtaining the above results extraordinary precautions were used to guard against the presence of any traces of inoisture. A train was used consisting of a 11)-drogen generator connected Ivith the usual purifying solutions and a final wash-bottle containing concentrated sulphuric acid ; the latter was attached to the hydroThis is the well-known experiment which, i n slightly modified form, Ostwald cites to illustrate what he calls chemical action at a distance.
l m t n i z ta iwozis C'hemicaI
React ioizs
7
chloric acid generator consisting of a flask containing coiicentrated sulphuric acid, into which conceiitrated hydrochloric solution could be dropped by means of a separating funnel. T h e liydrochloric acid gas generator was connected with a washbottle of concentrated sulphuric acid, and the latter with a tower (40 ciii high and 6 cni in diameter) filled with pieces of dr!. pumice covered with phosphorus pentoxide.x This tower was connected by a glass tube with the small flask containing the benzene atid substance to be tested. This flask was fitted with an excellent doubly perforated rubber stopper, and was in turn connected by a glass tube to another large tower filled with pumice covered with phosphoric anhydride. Before introducing the benzene and the dry substance to be tested into the flask, the latter, as well as its stopper and connecting tubes, was heated to drive off moisture ; and while these parts were still fairly hot, the benzene and substance" to be tested were quickly introduced ant3 the whole at once connected with tlie train. T h e air was then displaced with dry hydrogen ; arid finally, the hydrogen generator was cut off by i~ieansof a cock and the l~ydrocliloric ~ until tlie train was saturated. I n acid gas was s l o w l ~evolved making the precipitations with dry hydrochloric acid by passing the. gas into the oleate solutions in benzene, the same train and the same precautions were used. These precipitatioiis will 11ow be described.
'
I n these towers plugs of dry cotton were used to prevent any of the fine particles of phosphorus pentoside from being carried away. The method of drying the benzene has beeii given ahore. The metals were cleaned with eirierg cloth ( a new, fresh piece being used for each) and geiitly heated liefore introducing them into the benzene, except in the case of sodium and ~riagiiesiuni. The magnesium ribbon was simply thoroughly cleaned with emery cloth ; 011 account of the peculiar behavior of this metal toward hydrochloric acid ill benzene. several samples of magnesium ribbon of different makes were used, hut always with the same result. A sample of Schuchardt's best. zinc was also employed in additioii to the sample from Merck ; hut like the latter sample, i t was attacked invariably. The sodium was cut under dry benzc'tie and introduced very quickly into the flask. T h e carbonates were gently heated ; the sorliutn carbonate was prepared by fusing sodium bicarbonate i i i a platinum dish. The substances heated were. of course, introduced into the betixiie while still hot.
8
Louis Knhlenbeiy
When dry hydrochloric acid gas is passed into a solution of copper oleate in benzene, there is formed imi!mzz!(y a heavy brown precipitate which is cupric chloride. T h e reaction that takes place may be m i t t e n thus : Cil(C18Hjj02)2 1zHC1 = CuC12 - zCT8H3402.We have here then, a case of instantaneous precipitation by double decomposition which is perfectly comparable with that of the formation of silver chloride in aqueons solutions, when silver nitrate solution is treated with hydrochloric acid. I wish to emphasize again that these benzene solutioiis conduct no better than benzene itself. Even at the instant of the formation of the precipitate, there is not the least perceptible increase in the conductivity. I tested this by placing a copper oleate solution in the resistance cell with dynamo and galvanometer in circuit and then quickly pouring into the cell a saturated solution of dry hydrochloric acid in benzene. T h e precipitate forined instantly) bnt the galvanometer showed no change. T h e oleates of nickel and cobalt, when treated in benzene solutions with dry hydrochloric acid, react in a perfectlj. analogous manner. T h e precipitate from the nickel oleate solution is brownish yellow ; that from the cobalt solution is blue. It is hardly necessary to add again, that in these cases too the solutions are most excellent insulators. These freshly precipitated chlorides of copper, nickel and cobalt are generally contaminated with oleic acid, which adheres to them, especially if the solutions used are stronger than two or three percent. I t is moreover very difficult to n.as11 out this adhering oleic acid with benzene. If the precipitation is made in sufficiently dilute solutions, the amount of adhering oleic acid is slight, and may be washed out with benzene, as the following quantitative experiments show. 4.4510 g copper oleate were dissolved in zoo cc benzene. T h e solution was saturated with dry hydrocliloric acid gas ; the precipitate formed was filtered off on a dry weighed filter and washed repeatedly with benzene. T h e filtrate was shaken up with water and the mixture saturated with sulphuretted hydrogen ; there was no precipitate of copper sulphide, showing that precipitation in the benzene solution had
been complete. T h e precipitate and filter were weighed after being dried in the oven and cooled in a desiccator. T h e weight of the CnC12 was 0.9625, corresponding to 0.15538 Cu, or 1 0 . 2 2 percent ; the previous anal) sis yielded 1 0 . 0 2 percent ; theory requires 10.16 percent. T h e copper chloride was a bromn powder, soluble in water ; on evaporating the aqueous solution the characteristic crystals of CuC12 A- 2H20were obtained. 4.9376 g nickel oleate were dissolved in 2 0 0 cc benzene and treated as just described. T h e 5 ield was 1.05798 KiClz, corresponding to 0.4803 g Ni, or 9.73 percent Ni ; the previous analysis yielded 9.41 percent ; theory requires 9.46 percent. T h e brownish yellow chloride was still a trifle gummy, indicating that the adhering oleic acid had not all been washed out. 4.8793g cobalt oleate were dissolved in 2 0 0 cc benzene, and the solution treated as described above. T h e yield was 1.0275 g CoC12, corresponding to 0.4669 g Co, or 9. 57 percent ; previous analysis yielded 9 77 percent ; theory requires 9. j I percent. T h e blue powder was quite free from oleic acid, and dissolved in water with characteristic color. T h e filtrates from the chlorides cf nickel and cobalt were shaken up with water; the mixture was made alkaline with ammonia and tlien saturated with hydrogen sulphide. No precipitate was formed, indicating that in these cases too the precipitation in the corres2onding benzene solutions had been complete. Anhydrous stannic chloride is a most excellent insulator ; it was found that its conductivity is no better than that of air. Two samples, one from Kahlbaum, the other from Schuehardt, showed practically the same behavior ; these samples were in very securely closed, small glass stoppered bottles, and when it mas found that the liquids had such enormous resistance, no further attempts to dehydrate them were made. Stannic chloride mixes with benzene in all proportions, and such mixtures were found to conduct no better than benzene alone. In testing the conductivity, the method above described was used in all cases, ll'hen a solution of anhydrous stannic chloride in benzene is poured into a solution of copper oleate in the same solvent,
Lotris A7a/zZenbcv,v
IO
there forms i n s l a t t l ~ va heavy brown precipitate which is principally anhydrous cupric chloride. T h e reaction then may be written : ~ C L ~ ( Ct~SnC14 ~ H=~2CuCIz ~ ~ ~ Sn(C,8H3302)4. ) ~ The precipitate clings tenacioudy to some of the stannic oleate, which it drags down with it;' and it is, moreover, extremely difficult to free the precipitate froin the adhering oleate by repeated washing with benzene, because of the sticky, gummy nature of the precipitate. A dilute solution (about one percent) of copper oleate in benzene was treated with a slight excess' of a dilute solution of stannic chloride in the sarne solvent. T h e precipitate was filtered off and washed repeatedly with benzene. However, it always remained gummy. I t was dried in the oven to remove adhering benzene. 0.5640 g of this precipitate was treated with water. By far the larger portion dissolved, yielding a blue solution. T h e latter was finally boiled ; and the floating oily pellicle was filtered off and washed with hot water. T h i s oily pellicle was examined further. I t proved to consist of oleic acid and tin. A quantitative estimation of the latter was not made, because the sample was hardly large enough to warrant the attempt. T h e blue aqaeons filtrate was precipitated with silver nitrate solution. T h e silver ch!oride obtained weighed 0.9064 g, corresponding to 0.2241 g chlorine. T h e copper, in the filtrate froin the silver chloride, was determined as oxide. T h e ield of the latter substance was 0.24Sog, corresponding to 0.1982g copper. According to the formula CuCIz, 0.2241 g chlorine correspond to 0 . 2 0 1 0 g copper. T h e filtrate froin the first precipitate, formed by adding stannic chloride to copper oleate in benzene, was evaporated and finally carefully heated to I 14' to expel stannic chloride ; diiring this process the substance turned darker and possibly suffered slight decomposition. T h e residue was a dark, thick oily mass at rooin temperature. 2.5778 g of it was carefull-). ignited in a crucible, and the residue was evaporated repeatedly with concentrated nitric acid, and finally strongly ignited. T h e SnOz thtis obtained was white (showing
-
'
It was found that the calcillated quantity did not give complete precipitation of the copper.
'
that the precipitation of the copper had been complete) and weighed 0 . 2 53j g, corresponding to 0.2004g S n , or 7.8 percent Su; the formula (Cr8H3302)1Snrequires 9. j percent Sn. T h e tin found wa5 then 1.7percent too low for stannic oleate. T h e latter salt has to niy knowledge not been prepared heretofore. It is clear then that the reaction of stannic chloride on copper oleate in benzene solution is not what is commonly called a ‘(smooth ” reaction ; but tlie results are sufficient to show that it takes place in the main according to the equation above gii.en. Phosphorus trichloride, arsenic trichloride and silicon tetrachloride, obtained anhydrous it1 well-secured containers froni Schuchardt, were found to be miscible with benzene in all proportions. The solutions thus formed were tested and they proved to be insulators like the solution of SnCl4 in benzene. Yet i n each case when a solution of copper oleate in benzene is treated with a solution of PC13, XsC13, or SiCI4 in the same solvent, w p p e r is precipitated in form of a dark brown precipitate. T h e precipitate is essential1~-cupric chloride ; but it is in each case contaminated with some of the oleate, as in the case where SnC14 is used as precipitant. Oleates of phosphorus, arsenic and silicon have apparently not been prepared heretofore ; it will be interesting to see whether such compounds are stable enoagh to permit them to be isolated. T h e complete analysis of some of these precipitates and analogous ones from other oleate solutions, notably those of the oleates of nickel, cobalt, iiiaiigaiiese and iron, has been undertaken by Air, A. Koch, -4ssistant in ,%iialJ-tical Chemistry at this University. H e will in due time report tlie results of his investigations. TYe see then that HC1, SnC14, PCl , XsC13 and SiC14 each precipitate cupric chloride’ from benzene solutions of copper oleate. This is parallel to the fact that in aqueous solutions soluble chlorides precipitate silver chloride froni silver nitrate solutions ; and yet none of the above-named benzene solutions -
’
If a little water is added to such precipitates. t h e j turn greenish i n color ; in sufficient water the cupric chloride of course dissolves.
12
Louzs Knhlenberg
are electrolytes. If we mere to attempt to apply the terminology of tlie theory of electrolytic dissociation, we should have to say, -in benzene solutions the reagent for cupric ions is tlie chlorine ion ; but clearly this would be absurd, for these benzene solutions are non-conductors, i. e., they contain no ions. T h e solubility of these precipitates is also clearly diminished, as in the case of aqueous solutions of electrolytes, by adding the precipitant in excess. T h i s was noted i n particular when a solution of copper oleate was treated with just the calculated quantity of SnC14, the precipitation was not quite complete ; but on adding more of the precipitant the supernatant liquid became clear. l y e have here then in soliitions that are most excellent insulators, all the well-known phenomena of precipitation as they occur in the case of ordinary salts in aqueous solutions. n’hen hydrogen sulphide, dried over fused calciuiii chloride and finally over phosphorus pentoxide, is passed into benzene solution of the oleates of copper, nickel and cobalt (these solutions were dried as above described), the sulpliides of heavj. metals are at once thrown down. If these oleate solutions in benzene are first saturated with hydrochloric acid, so as to precipitate the chlorides, and then saturated with dry hydrogen sulphide, the sulpliides of the heavy metals do not form ; a slight darkening seemed to take place in tlie case of the copper. Stannic chloride dissolved in benzene was treated with dry hydrogen sulphide in large excess without any visible formation of sulphide of tin ; however, on standing over night a copious precipitate did form. Arsenic trichloride dissolved in dry benzene, showed similar reluctance toward forming a precipitate with drjhydrogen sulphide ; when petroleum ether was used as solvent the sulphide of arsenic formed almost instantaneoiisly. T h e petroleum ether was dried by tlie same method as the benzene. In his book on the theory of electrol) tic dissociation, H. C. Jones has compiled a list of experiments \vhicli show that water is necessary that certain reactions may take place. I wish to state definitely that I have no inclination to call any of the results of these
172stn 11 in tz eoiis Che m icaI K e a ct io 11 s
73
experiments into question but it is unfortunate that i n compiling Hughes’ experiments, Jones should have omitted the one’ that shows definitely that dry hydrocliloric acid does react with dry manganese dioxide. I t has been shown by Hughes3 that dry hydrochloric acid gas does not decompose the carbonates of calcium and barium ; I have stated above that these carbonates are also not decomposed by hydrochloric acid in benzene soliition. Hughes has also found that dry hydrochloric acid will not react with dry ainnionia ; this fact I have fully confirmed, and I wish to add, that this is the only case in which I attempted to confirm the experiments of Hughes, or the others listed by Jones. Yet when anhydrous benzene is treated with hydrochloric acid dried over sulphiiric acid and finally over phosphorus pentoxide, arid then ammonia (evolved by heating lime mixed with ammonium chloride, and dried by passing through a tower of lime and one of dry pumice covered with phosphorus pentoxide) is passed into the solution, a white bulky precipitate of aniinoniurn chloride at once forms ; the benzene vapors, moreover, are sufficient to cause the reaction to take place. In these experiments a train like that described above was used. I t was slightly altered, so that the hydrochloric acid gas generator could be cut out after the train had been saturated with the gas, and then the ammonia generator turned on so as to saturate the train with ammonia. Neither the solution of hydrochloric acid gas in benzene, nor the solution of ammonia in benzene, nor the mixture of the tit.0, conduct better than benzene itself; nor is there any change in the conductivity at the instant of mixiiig the ;I
X word of explation concerniiig one of Hughes’ experiments must be given here. The latter says (Phil. Mag. 35, 533 (1Sg3)), a n d I quote in full, “ An ‘ inactive ’ solvent. such as anhydrous ether in one case and benzene in another, was taken, and silver nitrate dissolved in it by warming. Through the solution a current of dry HCI gas was passed. For some time no change could be observed, and even after an hour only a very slight turbidity wasproduced.” This is readily explained by the fact that dry silver nitrate is practically insolu. ble i n dry benzene as well as i n dry ether, even on boiling, a fact of which I have assured myself. Phil. Mag. 35, 533 (1893). Ibid. 34, 1 1 7 (1892).
14
l m l a 12 tu m o z u Chem icn I React io 12 s
solutions. .%gain when anhydrous pyridine (dried for half a year with fused caustic potash, so that even the sharpest edges of the latter did not suffer the least change) is mixed with benzene, a solution is formed that conducts no better than benzene itself. Yet when such a solution is mixed with a solution of hydrochloric acid in the same solvent, there f o r m instantly a heavy white precipitate of the hydrochloride of pi-ridine. Dilute as well as strong solutions will show these phenomena. T h a t we can have instantaneons chemical reactions in solutions that are most excellent insulators, just as we have them in solutions that are electrolytes, is hereby established ; and therefore, whoever claims that the instantaneous chemical changes in aqueous, or other conducting solutions, take place because of the fact that these solutions are electrolytes (or i n current phraseology, because they contain ions), must assume the burden of proving his proposition. Laboratoiy of Physicad C/temistiy, 7'711 zarsity of Wiscousiz, Madisoa, LVis., Dec. 1901.
