FRIDAY, 4th.-Royal Institution, 9. "Applications of Electricity to Silicates of Soda and Potash in the state of

MR. VACHER will retire from the Chemical F. W. HART, Manufacturer and Dealer in

Chemical Works, Wolverhampton. Process.

EXTRACTOR OF COAL-TAR PRODUCTS.

JAMES WOOLLEY, SONS, & CO.,

69, MARKET STREET, MANCHESTER,

If it is admitted that Mn2O3 can be easily formed, a number of methods immediately suggest themselves as being likely to give the amount of manganese, prominent among which is the well-known method of treating with hydrochloric acid, and passing the resulting chlorine through a solution of iodide of potassium, the liberated iodine being titrated with sodium hyposulphite. ("Fresenius," fifth edition, p. 135). Accordingly I tried that method, but although I took every care, and returned to it again and again I completely failed to obtain accurate or even constant results. This seems strange (I may say that Mr. Parry had previously tried and failed also), and at first I attributed my failure to the fact that I was not getting Mn2O3, but was afterwards convinced that it is much easier to get that oxide than at first sight it appears. I can scarcely avoid coming to the conclusion that there is something wrong with this method of determining free chlorine.

The next method I tried proved in every way successful. I proceed exactly as Mr. Parry does (and find no difficulty in getting Mn2O3). 1 grm. of the speigeleisen is dissolved in nitric acid (sp. gr. 120) in a small round-bottomed flask, and evaporated to dryness. When dry the flame, which may be either a spirit-lamp or a Bunsen burner, is turned so that the bottom of the flask is cherry-red, for ten minutes. It is then allowed to cool very gradually.

At this point instead of forming carbonic acid, I simply put into the flask a weighed quantity of ammonio-ferrous sulphate or ferrous sulphate of a knowp strength, and

48

Properties Possessed by Certain Salts of Fulminic Acid.

least at first, of any gas or solid matter. The development,
of this colouration, under the circumstances stated, being
considered very singular, and hitherto unnoticed (as far as
I have been able to ascertain), led me to study the matter
more closely, to determine the nature of this coloured
compound, and of the changes taking place in its forma-
tion.

On prosecuting this inquiry, I further ascertained that when the purple compound was fully developed, if the heat was continued for some time, or more quickly if the temperature was raised to and maintained at the boilingpoint, the purple colour gradually disappeared, the liquid acquiring a light yellow tint, whilst more and more of a reddish brown solid matter (which was ascertained to be the peroxide of iron) was produced; these changes being accompanied by the evolution of more or less of ammonia, and by the mixture, which was at first quite neutral, acquiring a strong alkaline reaction. The solution being filtered, and concentrated by evaporation, was found to yield small prismatic crystals of a colourless or very light yellow salt, which appears to be a double cyanide of potassium and mercury.

Considering that the principal feature of interest in the reaction of the fulminate on the ferrocyanide was the formation of the purple compound, my attention was chiefly directed to its investigation. But I soon ascertained that this compound was a substance of a very unstable character, and that it presented great difficulties in the way of its separation from the matters with which it was associated, as procured in the reaction referred to; and not being able to obtain it in a pure or suitable state to submit it to actual analysis, I was for a considerable time unable to obtain any clue as to its real nature, further than it was some organic compound of iron, in which cyanogen, or at least its elements, were constituents.

At last it occurred to me that the colouration observed might be in some measure connected with the formation of the fulminate of iron; and on making some of that salt, and comparing its reactions with those of the compound referred to, many points of agreement between them were at once perceptible. I may observe that the fulminate of iron is readily obtained by the action of metallic iron on the fulminate of mercury suspended in water. Thus if about equal bulks of the fulminate and of fine iron filings are placed in a small stoppered bottle, which is then filled with distilled water, and being closed is occasionally agitated, the liquid in a short time acquires a yellowish tint, which gradually deepens in colour, whilst the filings become tarnished, and more or less of mercury, in the form of minute globules, make their appearance. After a few hours the decomposition of the fulminate of mercury will be more or less complete, and on filtering the mixture a dull yellow liquid is obtained, which holds the fulminate of iron in solution. This fulminate, as so obtained, was described by my late father amongst several other compounds of fulminic acid, which he was, I believe, the first 10 discover, during his elaborate researches on that acid. This salt was observed by him to produce, when treated with diluted acids, a fine red or purple colour, which disappeared after some time, evolving hydrocyanic acid amongst other products. He also found that a somewhat similar colour, rapidly changing to a bluish black, with a precipitate of that colour, was developed on heating this

fulminate.

But this development of colour only occurs in the case of the freshly prepared fulminate of iron, for the salt, being one of very great instability, commences almost immediately after its formation to undergo spontaneous changes, which are attended by the separation of a dark brown substance, even when the solution is kept excluded from the air in a well stoppered bottle: and after such changes have taken place it ceases to develop, either by the action of acids or by heat, the colouration just stated. My father also observed that alkalies produced in freshly prepared fulminate of iron a dull green precipitate, quickly changing to a brown colour, which is obviously due to the

CHEMICAL NEWS,
Feb. 4, 1876.

separation of iron as an oxide from the fulminate of iron
which remains after the action of the alkalies and the
And I have myself observed that the light yellow liquid
separation of the oxide at once develops a fine port-wine
colour when it is treated with diluted acids, and that the
developed by directly treating the fulminate of iron
colouration so produced is much more stable than that
similarly; and that this red- or purple-coloured compound
resembles in all its characters that produced in the new
reaction of the ferrocyanide on the fulminate of mercury
already referred to.

As to the singular development of colour when the ful-
minate of iron is treated with dilute acids, I am not aware
that any explanation has as yet been given; and the one
only in the case of the fulminate of iron, but also in the
that I would now suggest accounts for its production, not
new reactions which I have myself recently observed, and
coloured compound. To make the explanation I would
explains some of the properties of this curious purple-
offer intelligible, I should first observe that fulminic acid is
forming two classes of salts, viz., the neutral and the acid
generally regarded as a bibasic acid, which is capable of
salts. In the first, the two atoms of hydrogen in the
hydrated acid (H2C2N2O2) are replaced either by two
atoms of a monad metal, as in the case of the fulminate of
silver (Ag2C2N2O2), or by one atom of a dyad metal, as in
the fulminate of mercury (HgC2N2O2). In the second
whilst the other is replaced by a monad metal, as in the
class we have either one atom of hydrogen still retained,
case of the acid fulminate of silver (AgHC2N2O2), or two
atoms of hydrogen are retained (the molecule of fulminic
acid being doubled) where a dyad metal occurs, as in the
acid fulminate of mercury (HgH2(C2N2O2)2). Now as
we should express its neutral fulminate thus, FeC2N2O2:
iron in most of its combinations plays the part of a dyad,
and when this salt is treated with a diluted acid there is
formed, as I conceive, an acid fulminate of iron (a hitherto
undescribed salt) by the following reaction, where, for
2FeC2N2O2+H2SO4=FeH2(C2N2O2)2+ FeSO4
example, sulphuric acid has been employed,-
or purple colour, whilst it is at the same time much more
and that it is this acid fulminate which possesses the red
stable or less prone to decompose than the neutral salt.
If this acid fulminate is treated with an alkali its purple
colour disappears, owing, as I conceive, to the formation
of a neutral double fulminate of iron and the metal of the
alkali, which is a colourless salt in dilute solution; thus
in the case of potash being added to the acid fulminate of
and potassium formed, according to the following
iron, there would be a double neutral fulminate of iron
reaction:-
FeH2(C2N2O2)2+2KHO=FeK2(C2N2O2)2+2H20;

acid again develops the purple colour by the re-formation
and this colourless solution being treated with a diluted
of the acid fulminate, as the following equation indicates:-
FeK2(C2N2O2)2+H2SO4 = FeH2(C2N2O2)2+K2SO4.
Or, again, if to some freshly prepared fulminate of iron a
dilute solution of caustic potash be carefully added, the
mixture will continue (as I have observed) neutral so long
as the alkali produces a further precipitate of the oxide of
iron; and when it ceases to do so, if the mixture be then
filtered, a light yellow solution will be obtained, which
holds dissolved, as I conceive, a double neutral fulminate
of iron and potassium resulting from the displacement of
one-half the iron in the neutral salt, as is shown in the
following equation:—

2FeC2N2O2+2KHO=FeK2(C2N2O)2+FeO+H20;

and this double fulminate develops, as before observed, the purple colouration when treated with a diluted acid, and again becomes colourless, or very nearly so, on adding an excess of alkali, especially after the application of heat, and the colour can be again restored by acidifying the mixture, and these changes may be produced many times in succession.

For the production of the acid fulminate of iron the

NEWS

double neutral salt is much preferable to that of the simple neutral fulminate of that metal, as in the latter case there will be produced, as before shown, a proto-salt of iron, which reacts on the acid fulminate, occasioning its more or less rapid decomposition.

I may further observe that on heating the double fulminate just described there will be developed the red or purple colouration, unless there is present too great an excess of alkali. This remark, however, does not apply to the case of ammonia, the excess of which being expelled by heat does not interfere with its production.

This development of the acid fulminate by heat is not so easily accounted for as where it has been due to the action of acids; it may, however, depend on the circumstance that the simple neutral and double fulminate of iron, are both easily resolvable by heat under certain conditions into the acid fulminate.

I shall now point out how the explanation I have given of the production of the purple colouration in the case of the fulminate of iron may likewise serve to account for the similar development of colour, which I have myself observed, in the reaction of the ferrocyanide of potassium on fulminate of mercury. My experiments would seem to show, that when those compounds react on each other, there is at first formed, amongst other products, the double fulminate of iron and potassium, which, like that salt prepared directly, as already described, from the fulminate of iron, passes into the purple acid fulminate of that metal, on being heated or treated with diluted acids; the following formula and equation explaining the production of the double salt, accompanied, as it is in this case, by the cyanide of mercury and potassium :

2HgC2N2O2+K FeCy6=FeK2(C2Ñ2O2)2+

+2HgCy2+2KCy.

Amongst other facts which might be mentioned in support of the foregoing statement is the following one that I have observed, that when the ferrocyanide of potassium and the fulminate of mercury, along with water, react on each other at the ordinary temperature, the mixture after a short time acquires a yellowish tint, which gradually passes into that of a reddish shade; and if a portion of the mixture in this early stage of reaction be treated with a drop or two of any dilute acid, or is heated, the deep purple colouration which results when the double fulminate is similarly acted on will at once be developed. I shall now briefly notice some of the more characteristic properties of the acid fulminate of iron as obtained by the action of the ferrocyanide of potassium on the fulminate of mercury, most of my experiments having been made on that salt as so procured. When that compound is dissolved in water it appears to possess, at the ordinary temperature, considerable stability, for it has been exposed to the air and even light in an open vessel for several weeks without its appearing to undergo any change of colour; but when the solution is allowed, even spontaneously, to evaporate to dryness, the dark purple residue very soon passes to a brown colour, from the decomposition of this salt, and the separation of its iron in the form of peroxide; and this proneness to decompose in the dry condition may account for the residue not exploding on the application of a strong heat, the salt having quietly decomposed before reaching the temperature necessary to explode it or other fulminates; and I may further observe, that even in aqueous solution it soon decomposes if the temperature is raised to the boiling-point, its decomposition being attended with the separation of peroxide of iron and ammonia.

It does not appear to be soluble in ether, chloroform, bisulphide of carbon, or in benzol, though it is readily dissolved by alcohol.

It is quickly decomposed by strong acids, with the evolution of hydrocyanic acid and the development of Prussian blue, and even in their diluted condition the same occurs, but more slowly.

The caustic alkalies, at the ordinary temperature, slowly decolourise its solution; with the assistance, however, of heat that effect is quickly produced.

It appears to possess but little, if any, disposition to assume a crystalline form, for as yet all my attempts to obtain it separately in such a condition have been unsuccessful.

Several experiments were made as to the effects of dif ferent metallic salts on this compound, but no very characteristic results were observable, except in the case of the nitrate of silver, which produced a dull bluish precipitate, leaving the liquid colourless if sufficient of the silver salt be added. This precipitate, however, is one of great instability, for it very soon loses its blue colour (even when lying at the bottom of the stratum of liquid from which it has been precipitated), and becomes of a white or yellowish white appearance.

If, however, while it still retains its blue colour, it is treated with diluted hydrochloric acid, or with an alkaline chloride, the solution regains its original purple colour, whilst the chloride of silver precipitates; but if the addition of the acid or chloride be delayed till after the precipitate has become white, then both fail to reproduce the purple colouration, owing to the previous decomposition of the silver compound.

This red or purple combination appearing to be but little affected by many of the metallic salts seems to strengthen the view I have taken as to its nature, for had it been a peculiar cyanogen compound, such as we have in the case of the ferro-, ferri-, and nitro-ferricyanogen, as well as in other compound salt radicals of that substance, we should have expected that it would have produced very characteristic effects with different metallic salts.

I may further observe that the same compound is formed when the ferricyanide of potassium (or as it is better known under the name of red prussiate of potash), instead of the ferrocyanide of potassium (the yellow prussiate), in aqueous solution is heated along with the fulminate of mercury, and that it, as well as the ferrocyanide, even without the application of heat, give rise to, but more slowly, the formation of the red or purple combination, the ferricyanide acting, however, in this respect more readily than the ferrocyanide.

Lastly, I may add that I found that a similar purple compound was produced when the fulminate of silver was substituted for the mercurial salt in the reactions referred to, and that it is probable that some at least of the other fulminates would give rise to like effects.

I regret that the results which I have brought before the Academy are not, in some respects, of a more definite character; but all who have experimented on the fulminates have experienced the great difficulties of such enquiries, arising from their instability and complexity of constitution; but I hope before long to be able to investigate more fully the subjects of this communication, as well as other matters bearing on them. I trust, however, that the results of the observations which I have already made may not be considered as devoid of interest, as any facts which may extend our knowledge of fulminic acid (a compound regarding the true nature of which chemists are not yet agreed) must possess more or less interest in a scientific point of view; and it is well known that many facts and observations, which at first have been regarded as mere matters of interest to men of science, have afterwards proved of much practical utility.

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