DR. GLADSTONE ON THE COLOUR OF CHLORIDE OF COPPER. 211 XI.-On the Colour of Chloride of Copper in diferent States of Hydration. By J. H. GLADSTONE PH.D. F.R.S. THERE are two theories respecting the aqueous solutions of haloYd salts :-the one maintains that the compound of a metal and a halogen dissolves as such in the water; the other that it becomes a com- pound of the metallic oxide and the hydracid which is also dissolved in the liquid. One of the arguments adduced in support of the latter theory is that certain salts such as the chloride or bromide of copper or the chloride of cobalt change colour on dissolving in water and assume a tint which is supposed to belong to the oxide. It happened that in my recent investigation of circumstances that modify the action of chemical affinity I examined the changes of colour which take place when hydrochloric acid or a soluble chloride is added to a solution of a blue salt of copper.This led to an examination of the chloride itself; and the observations then made have been extended with a view to determine if possible how far the change in colour may really lend support to the theory in question. The following are the facts with which this examination has made me acquainted. Chloride of copper exists in a solid forni in two conditions the one anhydrous the other containing the elements of water. The anhydrous salt.-This is amorphous and of a yellowish brown colour whether produced by the combustion of copper in chlorine or by heating the hydrated compound.Its composition has been deter- mined by Berzelius and J. Davy to be CuCl. The hydrated salt.-This exists either in an amorphous or a crystalline form according to the mode of preparation. If anhydrous chloridc of copper be exposed for a few minutes to 1)R. J. H. GIAADSTONE ON THE COLOUR OF the ordinary atmosphere it begins to change from yellowish-brown to pale bluish-green. This will go on till the whole mass becomes a bluish-greet] powder which is dry to the touch not deliquescent in ordinary states of the atmosphere and devoid of crystalline form even when viewed under the microscope. Professor Graham believes this to be the hydrate CuCl 2130.* An experiment of mine confirmed this view. 0,960 grm. of anhydrous chloride of copper on exposure increased in weight to 1.224*grm.theory requires 1.216 grm. If the oxide or carbonate of copper be dissolved in hydrochloric acid and the solution evaporated nearly to dryness bluish-green crystals separate. Their forin has been determined as that of a right-angled four-sided prism. They are more deliquescent than the amorphous hydrate. No complete analysis of this salt seems to have been published. Its received forniula CuCl+2HO rests on the observation of Professor Graham that the crystals give off 21.53 grm. of water when strongly heated. I. 1grm. of the crystals dried at a temperature somewhat under 100' C. gave off 0.212 grm. of water when heated inore strongly and yielded 0.473 grm. of oxide of copper. 11. 1-22grm.gave 2.003 grms. of chloride of silver. 111. 1grm. of another preparation gave off 0.214 grm. of water when heated and afforded 0.472 grm. of oxide of copper. IV. 05 grm. of the same yielded 0.830grm. of chloride of silver. These red ts give percentage numbers nearly coincident with those deduced from the above formula. Found. Calculated. ..7-.-1st preparation. 2d preparation. Copper. . . 37.84 37-76 37.47 Chlorine . . 41.01 41.06 41.45 Water . . . 21.20 21.40 21*08 100.05 100*22 100~00 It is evident that this green salt may either be Cu C1+2 HO or CuO HC1+ HO. If the latter it might be reasonably expected that some difference would show itself between the two atoms of hydrogen and oxygen; but my observations though specially * Phil.Trans. 1837 p. 71. CIILOltLDE OF COPPER IS DIFFERENT STAPES OF HYDRA'I'ION. 213 directed to the point have failed to remark any. The brown salt appears to assume thc two atoms at once; neither is there auy inter- mediate stage in the dehydration of the green salt. When the crystals are heated to about 90' C. (1 9-4' F.)? they begin slowly to give off water shrink and assume at once the brown colour. If the temperature be raised a little above 100' C. the water is given off rapidly. If strong sulphuric acid be added to the green crystals or to a strong aqueous soluti.;nJ the hown salt is instantly produced. There appears then to be no ground for supposing that the difference of colour betweeu the anhydrous and the hydrated salt depends upon the conversion of the latter into hydrochlorate of the oxide of copper.33fect of solution.-If an equal weight of water be added to the pure green salt it dissolves giving a clear solution of a deep green colour. On the addition of more water a gradual change of colour occurs as indicated in the annexed table :-Composition of Solution. Colour. 1 part crystal. chloride of copper + 1part wdter 1)eep green. 17 JJ ,? 9 3-3 ? Bluish green. 7> ?i ,J >f +3 J Still blue. 99 JJ ,? , + 4 , Nearly pure blue. ,? ?> ?? 99 + 5 > Blue. Oxychloride of Copper.-lt may be as well to remark in this place that on dissolving most specimens of crystallised chloride of copper a white subsalt separates not when the solution is so strong as to appear green but when it passes from green to blue.This deposit was observed in one instance to be as much as -&ths of the whole weight of the salt though iisually it is considerably less than that. When dry it is a pale green powder which remains unaltered though heated up to 215' C. (419' F.)?but when almost at incipient redness it gives off both water and chlorine and is converted into a black mixture of oxide arid dichloride of copper. The following analyses were made :-I. 1 grrn. of the subsalt dried at loooC. and dissolved in dilute nitric acid yielded 0.734 grm. of oxide of copper and 0.812 grm. of chloride of silver. 11. 1 grm. of a different portion gave 0.760 grm. of oxide oi copper and 0829 grin. of chloride of silver. 111. 0.535 grni.of another preparatiou gavc 0.397 grm. of oxide of copper. UR. J. H. GLADSTONE ON THE COLOUR 01" These numbers reckoned to 100 parts represent- I. 11. 111. Copper . . . . 58-72 60.80 59.36 Chlorine . . . . 20.08 20.51 -The proportion of the copper to the chlorine appears thus to be as three atoms to one and though the salt is evidently somewhat irregular in its composition it approaches nearer to the oxychloride CuCl 2Cu0 HO than to any other of the eight or nine that have been described by previous investigators. Copper. . . 61.34 Chlorine . . 22.68 Oxygen and hydrogen . . 15.98 100~00 It isl probably this oxychloride with the admixture of a varying quantity of one containing more of the elements of water. Whether the constitution of this salt be as above written CuC1,2CuO €10 or 3Cu0 HCI there seems nothing to decide.This oxychloride dissolves in a strong solution of pure chloride of copper ;and the crystals derived from such a solution retain the form of the pure salt but are of a yellowish-green instead of a bluish-green tint; when dissolved in water they give an abundant deposit and they contain a deficiency of chlorine,-indeed in a case submitted to analysis only 39.75 per cent. The great disparity of tint observed in different specimens of crystallised chloride of copper seems to arise generally from the varying amount of oxychloride they contain though an excess of acid will also cause the crystals to assume a yellowish colour. Crystals that dissolve without deposit may be obtained from an impure salt by repeated solution filtration and recrystallisation though perhaps the chloride thus obtained is never absolutely free from subsalt.The best method of obtaining pure crystals is to start with a very acid solution. If strong hydrochloric acid not in excess be poured upon the oxychloride a solution results which on dilution deposits the subsalt. Change of coZour.-It has already been observed that the solution from which the oxychloride has separated changes gradually from a deep gifen to a clear blue. The question arises,-Does this change of colour depend npon some action of the water or of the elements of it ; or is it in some way a mere physical result of the solution ? In the hope of determining this inatter the action of other solvents CHLORIDE OF COPPER IN DIFFERENT STATES 01”HYDRATION.215 was tried. It was found that brown anhydrous chloride of copper dissolves in absolute alcohol of a yellowish-green colour and that it does not assume a bluish tint on any amount of dilution with the same solvent. This is the case also when either the bluish-green or yellowish-green crystals are dissolved in absolute alcohol or even in strong spirits of wine,-the alcohol appearing to abstract the water from the hydrated salt. Even the addition of alcohol to a moderately strong aqueous solution heightens the green imparting ayellowish tint to it. If the crystals contain oxychloride alcohol does not cause its separation. The addition of water in considerable quantity to the alcoholic solution causes a production of the blue colour and a deposition of any subsalt that may be present.If a solution of the anhydrous chloride in absolute alcohol be evaporated down it shows little or no tendency to crystallise but becomes an almost black viscid mass which however on standing for some hours becomes filled with tufts of yellowish-brown crystals. Ether in like manner dissolves chloride of copper giving an intense yellowish-green solution which also does not alter in the character of its colour when diluted with any amount of additional ether. The change from green to blue depends then upon the water; but is it because the salt is converted into hydrochlorate of oxide of copper or -because it forms a higher hydrate than exists in the crystals ? The following observations may possibly afford some grounds for forming an opinion.Hydrochloric acid imparts a bright yellowish tint to the green solution of chloride of copper. On dilution with water such a mix-ture also assumes a blue colour but it requires much more water than the neutral salt does. The followiiig table will exhibit the changes of tint produced during the dilution of a mixture of single equivalents of chloride of copper and hydrochloric acid. It would not dissolve completely in an equal weight of water. Coinpositioii of Solution. Colour. 1 part CuCl+ HC1 with 2 parts water Dark green. 5 1) Briglit yellowish green. >? >I 9 1) ,? I> 8 Bluish green. >9 Almost pure blue.>? >? 7 I¶ >> 9) 9) 15 I Blue. During this dilution there is a gradual alteration of the colour; but the change appears to be more rapid at certain points than at others. Yet after careful and repeated examination I caiiie to the belief that the effect of water is regular and that what appears like rather sudden DIL. J. H. GLADSTONE ON THE COLOUR OF transitiuns is due to the difficulty of comparing solutions of different shades of colour. If a solution containing single equivalents of chloride of copper and hydrochloric acid be diluted till it becomes blue the addition of more hydrochloric acid will cause it to resume the green colour and if sufficient be added to become of the bright yellowish tint,-the amount of greenness being regularly proportionate to the amount of hydrochloric acid present.The compound of chloride of copper and hydrochloric acid which niay be supposed to exist in these yellowish-green solutions does not appear to be crystallisable. If a solution of the copper salt in hydro- chloric acid be evaporated crystals separate of a bright green colour. On drying between folds of bibulous paper these part with the adhering strongly acid liquid and at the same time their yellowish tint is greatly reduced. A portion so prepared was dried at SO" C. when it appeared very like the ordinary bluish-green crystalline salt. It weighed 1.240grm. At a higher temperature -it gave off water and a little hydrochloric acid. After being heated at 150" C.it was converted into apparently the anhydrous chloride and weighed 0.969 grm. The same amount of CuCl 2HO would have given by calculation 0.979 grm.,-a quantity scarcely exceeding that actually found so that the hydrochloric acid attached to the crystals must have been a mere trace. Another experiilzeiit gave a similar result. That the brown powder left on heating this was really CuCl was proved by a determination of the copper. 0.531 gni. yielded 0.318 grm. of oxide of copper; which gives the following percentage :- Found. Calculated. Copper . 47.83 47.48 Some other chlorides,-such as chloride of sodium and chloride of ammonium,-produce the same yellowish colour in solutions of chloride of copper as hydrochloric acid does; whilst others such as chloride of calcium do not affect it.Some of these double chlorides have been crystallised and described. The colour of a solution of chloride of copper alters much with the temperature. If it be heated it becomes gradually yellower even if previously diluted to such an extent as to be perfectly blue. Indeed it was found that 2.5 grm. of the crystallised salt when dissolved in three ounces of water so that the blue colour was pale assumed a distinctly green shade when the solution was heated to the boiling point. The same occurs in the presence of hydrochloric acid. 011 CHLORIDE OF COPPER IN DIFFERENT STATES OF HYDRATION. 217 cooling again the yellow tint gradually disappears. This action also is not confined to temperatures above the ordinary a green solution of the chloride placed in a frigorific mixture becomes blue.The remarks here made upon solutions of pure salt in distilled water apply equally to the salt when produced by double decom position :-for instance to a mixture of sulphate of copper and chloride of sodium though of course in such a case the blue colour of the sulphate still unaltered interferes with the result. The addition of sulphuric acid to a somewhat dilute solution of chloride of copper tends to produce the bright green evidently from the liberation of some of the hydrochloric acid though blue sulphate must be produced at the same time. The following are the inferences which I have drawn from these experiments and which I now submit to the consideration of chemists :-Every observation made on this salt is perfectly explicable on the supposition that the proper colour of chloride of copper is brown and that it forms hydrates which are green or blue just as the white sulphate of copper becomes blue when hydrated.Some of the facts too are more easily explained on this view. Thus it is hard to imagine that if green be the colour of CuC1 and blue that of CuO HC.1 the addition of more HC1 to the latter should render it green; while it is readily conceivable that the hydrochloric acid should replace a portion of the water in the blue hydrated chloride of copper and form a green double chloride CuCl IICl. The action of heat is in harmony with what we know of its action on unquestionable cupric hydrates thus the hydrated oxide of copper when heated in the presence of any amount of water loses its combined water and its blue colour.If the change of colour is to be taken as evidence that crystallised chloride of copper hecomes when treated with a considerable amount of water CuO HC1 a parity of reason should lead us to conclude that the bluish-green crystals contain none of the yellowish-brown CuCl; yet if we suppose that these crystals actually contain the oxide we can give no consistent account of the subsequent chanse of colour on solution. Perhaps none of these observations are decisive on the point; yet it appears to me that this examination of the chIoride of copper has golie Far to show that instead of its furnishing an argument in favour of the supposition that haloid salts are decomposed by water it leads towards the opposite conclusion.218 DR. GLADSTONE ON THE COLOUR OF CHLORIDE OF COPPER. There are three incidental remarks which may be appended. Those who hold the binary theory of salts aud contend for the resolution of the chloride into the hydrochlorate must consistently suppose the same when the salt-radical is a compound body thus-If NaCl in water becomes NaO HCl 9, then NaNC , NaO HNC, 99 and NaSO , Na0,HS04. Even where different salts of a base have the same colour the same amount of the base does not give the same intensity of colour. Thus if equal portions of oxide of copper be dissolved respectively in acetic hydrochloric nitric and sulphuric acids and equally diluted the acetate will be found to be far deeper in colour than the nitrate this somewhat deeper than the sulphate and this again far deeper than the chloride.On being converted into ammoniacal salts these four approximate more nearly but are still far from identical in colour. Whatever theory be preferred for explaining the changes of colour that take place during the solution of chloride of copper the influence of mass is very apparent. It is almost self-evident that different compounds co-exist in the solution in proportions varying with the amount of water present or of free hydrochloric acid and that the final state of combination is the resultant of.severz1 affinities of dif-ferent degrees of strength acting on the same particles.