CUPRIC OXIDE JELLIES ____ BY I.,. S . FINCH
A cupric oxide jelly has been prepared by F0erster.l “If one adds an excess of ammonia to an aqueous solution of copper acetate and concentrates the deep blue solution on the water bath, one obtains acute-angled, beautifully violetcolored, prisms of copper acetate ammonia. There is always a precipitation of very finely divided copper oxide which, however, can easily be kept down to a minimum. If one wishes to avoid even this minimum, copper acetate should be dissolved in 93 percent alcohol and alcoholic ammonia added. When the excess alcohol is distilled off, the copper acetate ammonia crystallizes in a perfectly pure state. The salt can easily be recrystallized from strong alcohol, separating in the form of short prisms or of acute octahedra. It can be dried over sulphuric acid in a vacuum without decomposition. The composition corresponds to the formula C U ( C H ~ C O ~ ) ~ . Z N H ~ . ” Copper acetate ammonia dissolves in a verysmall amount of water forming a deep blue solution. If it is placed in a belljar over water, it deliquesces in the course of time. If a solution, prepared in either of these ways, be diluted, i t sets to a light blue jelly, which changes in time to a fine powder.” The first thing to do was to duplicate Poerster’s results. Copper ammonium acetate was prepared by adding ammonia to a saturated solution of copper acetate and heating very carefully on the water bath to prevent the formation of cupric oxide. This last can be prevented partially by the addition of alcohol. The desired salt crystallizes in purple octahedra which were washed with 95 percent alcohol and dried in a desiccator over concentrated sulphuric acid. They were then allowed to deliquesce over water. More water was then added and the solution shaken, whereupon a blue jelly was formed. While the upper part of the jelly looked all right, there was a precipitate in the bottom of the beaker. After 1
Ber. chem. Ges. Berlin, 25, 3416 (1892).
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the jelly had stood for an hour or so i t broke down into a light blue, gelatinous precipitate and a dark blue supernatant liquid. This method of forming a jelly was slow and difficult. So the copper ammonium acetate was washed with 95 percent alcohol and dried in the air. Water was added directly to the crystals instead of indirectly by deliquescence, and the mixture shaken. During the shaking the solution solidified to a blue jelly which was quite as good as, if not better than, the jelly obtained by Foerster’s method. The jelly was not permanent and broke down, as before, into a bluish precipitate and a blue solution. When left in an open beaker the water evaporated slowly, leaving a dry residue which had the appearance, under the microscope, of small chestnut burrs. If a little water is added to the dried mass and if the mixture is then shaken, the solution sets again to a jelly which before long breaks down as before. These operations can be repeated apparently indefinitely. Though these jellies had the merit that they could be restored by adding water to the dried mass, which was not the case with the chromic oxide jellies, they had the disadvantage of not being permanent. I tried to remove this defect by further purifying the copper ammonium acetate, by adding varying quantities of water, by keeping the jellies in a closed vessel or in a cool place. All these experiments gave negative results, though keeping the jelly in a cool place seemed to make it a trifle more stable. Instead of adding pure water, a 0 . 5 percent solution of gelatine was used. This retarded the breaking down of the jelly, but did not make it permanent. Next a I O percent sugar solution was tried. This was a distinct improvement, since a jelly made with this stayed up over night and later dried to a syrup. Even this jelly could not be called permanent. When making the original copper ammonium acetate solution, it was noticed that the solution thickened all at once when the proper amount of ammonia was added, almost giving a jelly. It was, therefore, thought that perhaps one could
L. S.Finch
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/
make a jelly direct from a copper acetate solution. Different amounts of ammonia were added to saturated solutions of copper acetate and suspensions were obtained which approached very closely to a jelly. This was markedly the case when using a supersaturated solution of cupric acetate. Substituting a ten percent sugar solution gave a better jelly, while gelatine seemed to have a tendency to precipitate the hydrous cupric oxide. None of these suspensions or jellies were really satisfactory because a gelatinous precipitate separated in time. They were quite as permanent, however, as those formed from copper ammonium acetate. Hence the only advantage of going through the copper ammonium acetate stage is to get the correct amount of ammonia automatically. Since manganese sulphate retards the change of the blue, hydrous cupric oxide into the black cupric oxidel making the former fairly stable a t IOO', it was thought that perhaps this salt might have a beneficial effect on the jelly even though the difficulty here is not the formation of black oxide. A small amount of crystallized manganese sulphate was added to the copper acetate solution, which was then allowed to stand for a few minutes before the ammonia was added. It was found that the presence of manganese sulphate prevented the immediate precipitation of hydrous copper oxide and caused the slow formation of a permanent jelly. Experiments were then made to determine the best amounts of ammonia and of manganese sulphate to add. For each experiment 50 cc saturated copper acetate solution were taken. The ammonia was concentrated ammonia diluted with an equal volume of water. The data for varying amounts of ammonia are given in Table I. From the experiments in Table I it is clear that a permanent jelly is obtained only by keeping within the limits of 3-4 cc ammonia. Experiments were also made with 2 . 5 cc and 3 .o cc ammonia but no manganous sulphate. In each case an immediate precipitate was formed which settled on Tommasi: Bull. SOC. chim. Paris, 99, 37 (1884).
121
37, 197 (1882);Comptes rendus,
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standing. In Table I1 are given data for varying amounts of manganous sulphate. These are not as accurate as they should be, because unfortunately care was not taken to be certain that all the manganese salt had dissolved before the ammonia was added:
TABLE I 50 cc saturated copper acetate solution; diluted ammonia (I : I ) ; I
__-
gram crystallized manganous sulphate
NHiOH cc 2
4 6 8 2
3 4
5 2.5
3.5 4.5 2 . 8 2.2 3.2
2.8
. .
_________
- ~ _ _ _ _ _ _ .
Quality of deposit
Light blue precipitate on standing Permanent blue jelly (slight brownish tinge) Gelatinous precipitate, solution brown Quick-settling precipitate, solution brown Light blue precipitate on standing Permanent light blue jelly Permanent blue jelly (slight brownish tinge) Gelatinous precipitate, settles slowly Jelly, not permanent; nearly colorless solution Permanent light blue jelly Jelly, not permanent; brownish solution Jelly, not permanent Jelly, not permanent Permanent blue jelly Jelly: not permanent
TABLE I1 (I
:
5 0 cc saturated copper acetate solution; 3 cc diluted ammonia I ) ; crystallized manganous sulphate
MnSOa.7HzO Grams I
.o
3.0 5.0 10.0
7.0 4.0 0.5 0 . 2
Quality of deposit ____
Fair jelly Fair jelly but settles somewhat in two days Jelly, not permanent Jelly, not permanent Jelly, not permanent Jelly, not permanent Permanent blue jelly (excellent) Permanent jelly but darker colored a t bottom
.~ ~
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L . S. Finch
From the experiments in Table I1 we see that the best results are obtained with about 0.5 gram manganous sulphate. Increasing the amount of ammonia or decreasing the amount of manganous sulphate darkens the color of the jelly. It had been assumed that the manganese radical was the effective one in making the cupric oxide jelly permanent and consequently still better results were expected from manganous acetate. This anticipation proved ill-founded. Manganese acetate gave rise to a mushy suspension which was not a jelly. Manganese nitrate, carbonate, phosphate, and oxalate were added to the solutions and had no beneficial effect. When one gram manganous chloride was added, a very good light blue suspension was obtained but no jelly. With lower concentrations of chloride, the precipitate settled more rapidly. The sulphate is thus the only salt which causes the formation of a jelly when added to an acetate solution. The chloride prevents immediate precipitation but the suspended particles do not coalesce to form a jelly. These experiments raised the suspicion that the manganese radical was not the important factor, in which case the sulphate radical must be. This appeared to be negatived by the fact that copper sulphate does not give a jelly when treated with ammonia. It behaves like copper nitrate or cupric chloride. I t was thought a good plan to try experiments with a solution containipg as few ions as possible and consequently hydrous copper oxide was formed from copper nitrate, copper sulphate, and copper acetate solutions. The different precipitates were filtered and washed as clean as possible from adsorbed material. They were then dissolved in ammoniawhich does not take place readily-and the ammonia removed by means of a suction pump. No jellies were obtained, the hydrous copper oxide reprecipitating as the ammonia was removed. The sulphate problem was therefore attacked again. The easiest way to reconcile the good effect of manganous sulphate with the fact that copper sulphate gave no jelly was to postulate that a small amount of sulphate was beneficial
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while a large amount was not. Adding manganous acetate and a few drops of sulphuric acid gave rise to a good jelly when ammonia was added. This differed from the earlier experiments in that the manganese and the sulphate were no longer present in equivalent quantities. I then discarded the manganese salt and added sulphuric acid in small amounts to the copper acetate solutions. The experiments were successful. On adding ammonia, good permanent jellies were obtained which were of a lighter blue than when manganese was present. When these jellies were allowed to stand for several weeks in open beakers, tKey dried to a powder which resembled chestnut burrs in appearance. When shaken with water a solution was formed which set to a permanent jelly. The process could be repeated once more, and probably indefinitely. The best jelly was obtained by taking 50 cc saturated copper acetate solution, four drops of concentrated sulphuric acid, and 3.5-4.0 cc diluted ammonia ( I : I ) . With two drops of sulphuric acid the jelly was not permanent though (or because) i t formed more rapidly than when drops of acid were used. With more than ten drops of acid, the jellies were not good. Adding hydrochloric acid instead of sulphuric acid was not successful. On the other hand, potassium sulphate gave as good a jelly as sulphuric acid. From all this, it seemed to follow that a suitable mixture of copper acetate and copper sulphate solutions should yield a good jelly though neither of them will do so separately. I mixed 47 cc saturated copper acetate solution with 3 cc saturated copper sulphate solution and added ammonia. Duplicate experiments were made and jellies were obtained which stood up admirably for a week and then broke down suddenly. I t is probable that other mixtures would have been really permanent, but there was not time enough in which to try this. The general results of this paper are: I . When copper ammonium acetate is shaken with water, a jelly is formed which is not permanent. If the decomposed jelly is allowed to evaporate to dryness and the residue is
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L. S . Finch
shaken with water, a jelly is formed which is also not permanent. The process can’ apparently be repeated indefinitely. 2 . When copper ammonium acetate is shaken with a ten percent sugar solution, a somewhat more stable jelly is formed. 3 . It is not necessary to start with copper ammonium acetate. The same results can be obtained by adding a suitable amount of ammonia to a saturated copper acetate solution. 4. No jelly is obtained by adding ammonia to a copper sulphate] copper nitrate, or cupric chloride solution. 5 . If a small amount of manganous sulphate be added to a saturated copper acetate solution, a permanent jelly is obtained on adding a suitable amount of ammonia. 6 . The amount of ammonia must be kept within fairly narrow limits. 7. The jelly is darker in color with high concentrations of ammonia or low concentrations of manganous sulEhate. 8. Other manganous salts do not act like the sulphate] though the chloride comes nearest to it. 9. It seems probable that the manganese radical has little or no effect in making the jellies permanent but that a low concentration of sulphate is the important thing. IO. The manganous sulphate can be replaced successfully by sulphuric acid or by potassium sulphate. 11. It did not prove possible to substitute hydrochloric acid for sulphuric acid. 1 2 . A mixture of 47 parts of saturated copper acetate solution and 3 parts saturated copper sulphate, when treated with ammonia, gave a jelly which stood up for a week. By changing the ratio, it is probable that a permanent jelly could be obtained. 13. If a permanent jelly, containing sulphate, be allowed to dry to a powder, a permanent jelly can be regenerated by shaking the dried mass with water. 14. The best jelly was made by mixing 50 cc saturated
’
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copper acetate, 4 drops of concentrated sulphuric acid, and 3-4 cc diluted ammonia ( I : I ) . 15. It was not possible to prepare a jelly by dissolving washed hydrous cupric oxide in ammonia and removing the ammonia with a suction pump. This investigation was suggested by Professor Bancroft and has been carried on under his supervision. Cornell University
