NOTE ON COLL,OIDAL NICKEL HYDROXIDE
BY 0. F. TOWER
I n an article1 published about a year ago reference was made to the peculiar behavior of nickel hydroxide formed in a glycerine solution. This has been investigated further in order to ascertain what concentrations of the con- . stituents are necessary to bring about the results observed. In the first place a solution was prepared containing 4 grams Ni(CzH30J2. 4Hz0 in 10%C.C. of Baker’s C. P. glycerine. The most favorable.conditions for reproducing the behavior just referred to were obtained by mixing I B C.C. of this solution with 8 C.C. of normal potawium hydroxide in alcohol. This set to a jelly within 24 hours and later syneresis began, sometimes slower, sometimes faster, but in general the same stages were observed as described in the previous paper. I n case relatively less of the potassium hydroxide solution were employed, either no jelly formed or only a very mobile one; with more potassium hydroxide solution, the jelly was much firmer but little or no syneresis occurred. Two new methods of preparing colloidal nickel hydroxide will now be described. I. To 24 C.C. of the glycerine solution mentioned above was added I O of normal potassium hydroxide in alcohol and IO C.C. additional alcohol (95 yo). These were shaken together thoroughly and the resulting solution remained clear and limpid indefinitely. After several days standing this could be diluted with water without precipitating nickel hydroxide, and, after dialyzing, a clear gelatinous m a s of the hydroxide remained. C.C.
By carefully warming it WRS found that IOO C.C. of glycerine would 2. dissolve 6.7 grams of nickel acetate, although some acetic acid was lost in the process. To 16 C.C. of this solution was added 6 C.C. of normal potassium hydroxide in alcohol and 2 C.C. of distilled water. When such a mixture does not gelatinize, which occurs about two-thirds of the time, after standing several days it can bediluted with water without producing a precipitate. When this is dialyzed a clear semigelatinous mass of nickel hydroxide remaine. The most rapid method of obtaining a colloidal solution of nickel hydroxide is that given in the former paper (p. 731). Additional proof has been obtained that the peptization of the hydroxide is due to small amounts of potassium chloride remaining in the solution. Nickel hydroxide was prepared as described there, but was settled by means of a centrifuge, and by this means 1
Tower and Cooke: J. Phys. Chem. 26,733 (1922).
NOTES ON COLLOIDAL NICKEL HYDROXIDE
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I77
the amount of potassium chloride remaining mixed with the precipitate could be regulated very exactly. After settling by this means additional distilled water was added, the precipitate settled again by centrifuge, and this continued as long as desired. The precipitate could be washed fifteen times this way in an hour and a half, which would remove the potassium chloride practically completely. Nickel hydroxide prepared in this manner and left standing in distilled water over night would not go into colloidal solution. Neither would it, if it were washed by centrifuge only two or three times, for in this case too much potassium chloride was present. However, if it were washed this way six or seven times and allowed to stand in contact with distilled water it would pass into colloidal solution in a few hours. To see whether nickel hydroxide, as it is ordinarily precipitated from solutions as an apple-green gelatinous mass is really Ni(OH)z or is NiO with adsorbed water, a method used by van Bemmelen' in investigating gelatinous silica and ferric oxide has been employed. Samples of nickel hydroxide obtained by precipitating both from hot and from cold solutions were used. These were air-dried, pulverized, and left in a vacuum desiccator over sulfuric acid of increasing concentration until the weight became constant. The t,emperature of the room in which the desiccation was carried on was maintained at 20' & I O , The samples were kept on watch glasses with ground edges, and during weighing this was covered with a second one clamped tightly to it in order to prevent absorption of moisture from the air. Weighings were made every day and continued until the weight became constant. The sulfuric acid in the desiccator was then replaced by the next more concentrated solution, and the process repeated until finally the weight became constant over the g 8 y o acid. Sulphuric Acid in Deeiccator Tension of Percent- Density Aqueous Vapor at Composition age at 2 0 0
1
-I
1
2 oo
I .416 1.473 I.547 1.647 1.774 I ,836 I
mm. 5.79 3.73 2.24 0.85 0.15
--
Sample I. Sample 2. Grams Grams Orig. Wt. 2 . 3 9 0 2 2 . 3 0 2 0 After 2 wks 2 . 3 8 0 8 2 . 2 9 7 2 After 3 wks 2 . 3 2 2 1 2 . 2 4 6 5 After 3 wks 2 , 2 5 1 6 2 . 1 8 4 3 After 3 wks 2 . 1 8 9 5 2 . 1 2 5 1 After 3 wks 2 . 1 8 5 8 2 . 1 2 1 7 After 2 wks 2 . I S A C 2 . 1 2 0 0
In the accompanying table the first three columns give the composition and density of the sulfuric acid used, the fourth column gives the tension of aqueous vapor over the acid, and the fifth and sixth columns give the weights of the samples of nickel hydroxide after constancy had been attained over the . corresponding solution of sulfuric acid. Z. anorg. Chem., 13,315 (1897)
i,
178
0.F. TOWER
Sample I was prepared from hot solutions and sa.mple 2 from cold solutions. No difference was noticed in their conduct, except that sample 2 was a little more hygroscopic after it was dry. The loss of water in both samples was fairly regular and shows no probability of the existence of a hydrate over the range investigated. The composition of the final material was determined by estimating the nickel electrolytically with the following results : Percentage found
Sample I 63 * I 4
Sample 2 63.08
Theoretical for Ni(0H)z 63 a 3 0
The substance dried to constant weight in a vacuum over concentrated sulfuric acid therefore appears to be Ni(OH)2 and not NiO or any intermediate hydrate. Morley Chemical Laboratory, Western Reserve University, Cleveland, Ohio.
