RAY : F~SCHER’S SALT AND ITS DECOXPOSITION BY HEAT. 551

LVII1.-Fischer’s Salt and its Decomposition by Meat, By PRAFULLA CHANDRA RAY,

To the potaseium cobaltinitrite, named after its discoverer, is generally assigned the formula K,Co2(N0,),,,3H20. According to Sadtler, however, ‘‘ this salt can be formed with 4H20, 3H,O, 2 H,O, H,O, or anhydrous, according to the degree of concentration of the solution used, passing in colour from a light yellow to dark greenish-yellow, and that in consequence of such dependence, we can, in most preparations, fix no absolute point, but are liable to have a mixture of salts of different degrees of hydration ” (Amer. J. Sci., 1870, [ii], 49, 192).

Roeenheim and Koppel, who have recently investigated the subject, find that in order to obtain the salt in a state of purity it is necessary to pass a current of nitrous anhydride the product of the action uf arsenic trioxide on nitric acid into a solution of potassium nitrite holding in suspension cobalt carbonate. The product thus secnred has the formula K,Co,(NO,),, (Zeit. anorg. Chem., 1898, 17, 35)”

Although my immediate object in view has been to study the decomposition products of this compound under the action of heat, the results could scarcely be relied on until the main question of its com- position was satisfactorily settled.

The following methods of preparing the salt were therefore ex- amined.

I. Preparation of the Double Xcdt.

Method A.-(cL) A strong solution of potassium nitrite acidified with acetic acid was added to a fairly concentrated solution of cobalt chloride, care being taken that the whole of the cobalt was not pre- cipitated. After standing overnight, the precipitate, which was of a light yellow colour, was collected on the filter paper and washed, first with a solution of potassium acetate and then with 90 per cent. alcohol, and dried by being allowed to remain under pressure between the folds of blotting paper.

( b ) The method was much the same as above, the only difference being that a large excess of potassium nitrite was taken. The filtrate was free from cobalt, but had a pale green colour, due to traces of nickel.

(c, d, e ) A systematic study of the composition of the salt was desirable ; with this object in view, three solutions were prepared : (1) of potassium nitrite of sp. gr. of 1.27 ; (2) of cobalt chloride of SP. gr. of 1-16, and (3) of acetic acid containing 25 per cent. of glacial acid and mixed in the following proportions.

* My information is derived from the abstract of the paper (Abstr., 1898, ii, 439). VOL, LXXXIX. 0 0

The mother liquor in both (i) and (ii) was distinctly acid.

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552 RAY : FISCHER'S SALT AND ITS DECOMPOSITION BY HEAT.

COCl, KNO, Acid No. solntion. solution. solution. Remarks.

I. 25 C.C. 25 C.C. 5 C.C. Colour of the sal t : greenish- yellow. Mother liquor : pink, showing t h e presence of excess of cobalt. Reaction : very feebly acid = c.

11. 25 C.C. 50 C.C. 5 C.C. Mother liquor gave faintly al- kaline reaction ; the sample was consequently rejected.

111. 25 C.C. 25 C.C. 10 C.C. Colour of tho salt : pale yellow. Nother liquor: pink, bu t less so than i n No. I. Reaction dis- tinctly acid=d.

IV. 25 C.C. 50 C.C. 10 C.C. Colour of tho salt : dark green- ish yellow. Mothm liquor : pale green, free from cobalt, with feebly acid reaction = e .

For convenience of reference, the results of analyses of the different preparat,ions are presented below in a tabulafieti form.

Designation Percentage of

preparation. Co. li. H,O. Remarks. of *-

a 13'42 25-12 4'31 Theory for Co,(N0,),,61~N0,,3H20 re- quires Co = 12 t i 7 ; K = 24-99 ; H,O = 5-75 ; N = 17.90. *

b 12-68 24.85 8'48 Theory for Co,(NO,\,, 6KN0,,4f120 re- quires Co=12'34 ; K=24-52 ; H20= 7-53 ; N=17*54.

d 13.45 25'3 2.90 Theory for the dihydrated salt requires C0=12*82 ; I<=25'48; H,O=3.91.

quiresCo=13.07; K=25*99; H,O=1*99.

C 14-04 25.14 398 -

e 13.57 25'18 2-56 Theory for the monohydrated salt re-

* (Co=59 ; 0 = 1 6 ; Richards and Baxter.)

It mill be seen that, judged by the percentage of water alone, preparation a approximates to a salt with 3 molecules of water, and b to one with 4 molecules of water, whilst d and e would lie between a mono and a di-hydrated salt. Two more preparations according to methods described under a and b gave the percentages of water as 6-35 and 5.64 respectively. As all these preparat,ions were simply air-dried, the percentage of water seemed t o be more or leas a matter of accident, depending on the hygrometric state of the at- mosphere. The percentage of cobalt came out invariably too high, and potassium as a rule too low. As the method of analysis was one which admitted of a high degree of accuracy (see fOOthOt,e on p. 554), this anomaly could not be explained. Another series of preparations was undertaken, in which special care was taken to obtain as pure a product as possible. Ordinary cobalt chloride, as supplied in the laboratories and labelled (( pure," was dissolved in water and treated

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RAY : FISCHER'S SALT AND ITS DECOMPOSITION BY HEAT. 553

U .

T 11.

Co ..... 1 3 2 6 13'19 I< ......... 25-03 25-02 H,O ...... 6'30 6-40

with sulphuretted hydrogen in order to remove any traces of the metals of the copper group (Chem. News, 1898, 77, 22). The filtrate was evaporated down to a small bulk, from which, on standing overnight, cobalt chloride crystallised out. I n some cases, the cobalt solution was fractionated with ammonia, although, as pointed out by Richards and Bsxter, this method is of doubtful advantage (Chem. News, 1900, 81, 140).

A concentrated solution of cobalt chloride thus purified was acidified with acetic acid and an insufficient amount of potassium nitrite solution added to it. The precipitate was collected after eighteen hours and washed as before, but dried in the steam oven.* The mother liquor, which was distinctly rose-coloured, was now treated with a solution of pure potassium nitrite to which acetic acid had been just previously added. The precipitate collected after twenty-four hours was washed and dried exactly as above. The mother liquor was still decidedly of a rose colour. This time a sufficient excess of potassium nitrite acidified with acetic acid was once more added, and on the next day the precipitate was collected as usual. The mother liquor was now found to be faintly green owing to the presence of nickel. The analyses of the three successive fractions a, p, and y are given below. It will be noted tbat although formed under widely varying conditions their composition remains practically constant.

B. - i. 11.

c o ...... 13.34 13-49 K ......... 24'17 24-10 H,O - - ......

7. - Theory for i. ii. CO,(NO,)~ ,~KNO,, 3H,O.

c o ............ 13.33 13'32 12.57 K ............... 24-51 24.60 24.99 H20 ......... 4 -75 4-80 5.75

Tn determining the composition of the salt, the percentages of the two metals and of water have been regarded as sufficient evidence, b u t several estimations of nitrogen have, however, been made, as will be seen in the second portion of this paper.

The most favourable conclusion which can be drawn from the above investigation seems to be tha t a aalt of the composition of

Co,(NO,),,6KN0,,3H,O is uniformly formed, but that it carries down with it traces of an oxide of cobalt, thus increasing the percentage of this metal and

* At loo", this compound does not undergo decomposition, 0 0 2

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554 RAY : FISCHER'S SALT AND ITS DECOMPOSlTION BY HEAT.

m Co ... 13-68 13.78 13.71 I< ... 24.01 - - H2O. 4.53 - -

lowering that of potassium." Preparations d and e would, to a certain extent, go to support Sadtler's views, namely, that the hydration and colour of the salt depend on the concentration of the solutions used,

i?.-i. Co ... 13.68 13-60 13.70 K ... 24.0 24'01 -

33. Rosenlbeim and Koppel's Method.

The products of this method of preparation had a more attractive colour, with all the gradations of t in t varying from orange yellow to lemon-yellow. The analyses of several distinct preparations are given below :

Ir. 1. 11.

Co ... K ... ... - -

It will be seen that the cobalt in this series of preparations is even much higher and the potassium correspondingly lower than in those of method A, and the conclusion which has already been drawn is further confirmed.

A modified method was found to give better results. Nitrous fumes were passed into water holding in suspension cobalt carbonate until a perfectly bright, clear, rose-coloured solution was obtained. A solution of potassium nitrite was similarly treated until red fumes began to be evolved. The latter was then added to the former and the mixture set aside until the mother liquor became quite quiescent, The precipitate was washed as usual and dried in the steam chamber.

Found. - Theory for i. ii. Co,(NO&GKN02.

Co ............ 13.09 12.96 13-34 K ............... 24-39 24.37 26.62 H20 ............ 4 -31 - I

Judged by the percentage of cobalt alone, one would naturally take this last preparation to be anhydrous, yet not only is the percentage of potassium too low, but the salt is found to be actually hydrated. I n fact this is the nearest approximation to a trihydrated salt.

It is thus evident that Rosenheim and Koppel's method can scarcely be regarded as an improvement on the ordinary one, and that it really yields a trihydrated salt contaminated as before with appreciable quantities of some oxide of cobalt,

* The potassium acetate solution with which the salt has to be washed is not completely removed when subseqnently treated with alcohol. Hence, as a rule, the percentage of potassium comes out higher rather than lower.

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RAY : FISCHER'S S A ~ T AND ITS DECOMPOSITION BY HEAT. 555

11. Decomposition 69 Heat. [With ATUL CRANDRA GANGULT.]

Erdmann found that Fischer's salt on heating evolves nitrous acid. The method of experiment followed was exactly the same as already described (Trans., 1905, 87, 180). As, however, no nitrous fumes were evolved, the interposition of the glass spiral packed with glass beads previously moistened with caustic potash solution was obviated. It was found that the decomposition proceeded according to the following equation :

C O ~ ( N O , ) , , ~ K N ~ ~ , ~ H , O = Co,O, + 6N0 + 3KN0, + 3KN0, + 3H,O.

I n other words, half the amount of the total nitrogen in the salt is given off as nitric oxide,? A t the same time an internal oxidation takes place.

Found, Calculated. Nitrogen, total .................. 17-15" 17-90

,, as nitric oxide ...... 8 3 5 8 *95

* The total nitrogen was estimated according to Dumas' method and varied in the several preparatioiis from 16.82 to 1'7'48 per cent.

This result represents the mean of more than a dozen experiments. After the reaction was over, the residue was exhausted with hot water, and the filtrate on analysis gave the remaining half of nitrogen made up of equal proportions of nitratic and nitritic nitrogen. Traces of nitric oxide begin to be given off below 200'. At 203O, the evolution proceeded regularly but very slowly, the reaction not being completed in less than eight hours. The most favourable temperature was found to lie between 210' and 215'. If the salt is heated in an air-bath instead of in a vacuum, the whole of the potassium nitrite is converted into nitrate. I n this case, the nitric oxide previously set free evidently acts as a carrier of oxygen from the air.

111. The Analysis of Piischer's Salt.

Cobalt is often separated from nickel and other metals in the form of this salt. The estimation of cobalt and of potassium involves a tedious and laborious process. The latest authoritative work (Moissan, Chimie Mineraze, vol. iv., pp. 152 and 200) gives a method which is practically the same as that employed by m e eighteen years ago in the analysis of nickel, cobalt, and potassium su1phate.S With

* " Es entwickelt dabei saltpetrige saure " (J. pr. Chent., 1866, 97, 401). f The nitric oxide was invariably found to contain traces of carbon dioxide, no

doubt from the decomposition of potassium acetate, which adheres tenaciously to the double salt.

$ " Conjugated sulphates of the copper-magnesium group " (Proc. Boy. Edin6urgh, 1888).

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556 HAWTHORNE : THE CONSTITUTION AND

the experience gained in the present investigation, the following expeditious method mas devised. The salt is weighed out in a crucible which is placed in an air-bath at a temperature of 215-220' for about a couple of hours or less. The residue in the crucible is then transferred to a porcelain basin and repeatedly washed by decantation with boiling water before being collected on the filter, care being taken not to wash it further a t this stage, as otherwise the oxide has a tendency to run through. Traces of oxide which adhere to the basin should be wiped off by means of a moistened filter paper. The cobalt is estimated according to Rose's method. The reduced metal may be washed once more with hot water to remove traces of alkali and again reduced in a current of hydrogen. It has been found, however, that the difference in weight after this treatment seldom exceeds a milligram; the potassium in the filtrate is weighed as sulphate. The chief recommendation of the method lies in the fact that it dispenses with the use of ammonium sulphide, caustic alkali, or of any reagent whatever. To judge of the degree of accuracy attainable, the reader is referred to the foregoing tables of analyses.

CHEMICAL LABORATORY,

CALCUTTA. PRESIDENCY COLLEGE.

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