Art. LX.—On the Analogy of Cyanogen to Oxygen.
[Read before the Wellington Philosophical Society, 29th August, 1874.]
I Have to preface my remarks upon this subject by the statement that they are entirely of a theoretical nature, and therefore unsupported by the results of that kind of experimental research, the details of which it will be remembered have hitherto constantly formed the groundwork of those previous papers of mine read before you; however, for this once I must beg your kind indulgence for a hearing upon that which, if it has any value, owes it to chemical researches and chemical records, long since accumulated by other chemists.
Presuming then upon your indulgence, I will at once state that the subject of this paper is the true position of a certain compound body among the elements as deducible from its known chemical reactions, that now assigned to it being, I think, incorrect.
The great importance of interpreting those facts correctly by which we compare our imitative with our real elements, is so obvious to those anxious to apprehend more of the true nature of the elements than at present we do, that I need not excuse myself for bringing such a matter as this before you.
The substance, the supposed position of which I take exception to, is cyanogen, a compound as you are aware of carbon and nitrogen in equivalent quantities. It and a number of other compounds into which it enters are now classed indiscriminately and collectively with the chlorine group as salt radicals, but to cyanogen itself “par excellence” is attributed this character.
That this is in reality the position assigned to cyanogen is indisputable. Brand and Taylor in their excellent work on chemistry, designate this substance as a compound radical and associate it with chlorine, bromine, and iodine for reasons I shall presently show. Prof. Roscoe too in his Elementary Chemistry, 1871, describes cyanogen in terms which certainly have a tendency to keep it so classified. The special grounds upon which cyanogen is classed with these radicals are, I believe, as follows:—
That it and its hydride combine directly with the least oxidizable metals generally, as gold and silver.
That it also combines with hydrogen and forms with it a compound analogous to hydrochloric acid.
That when passed into a solution of any caustic alkali it is in part oxidized, alkaline cyanates and cyanides forming.
That when cyanides are electrolyzed the radical is evolved at the positive pole.
If to this we add that cyanide of potassium crystallizes in cubes, as do the chlorides, bromides, and iodides of this base, I think we exhaust the evidence which can as yet be alleged in favour of the analogy of cyanogen to the elements referred to.
Such are the reasons for classifying cyanogen with these radicals, and I will now go over them seriatim.
In the first place it is true that cyanogen combines directly with the least oxidizable metals, but so does oxygen when in the allotropic state, also sulphur at a slight elevation of temperature, and further its hydride (sulphuretted hydrogen) imitates hydrocyanic acid in presence of the metals instanced; oxygen and sulphur should therefore on this principle be admitted along with cyanogen into the group of radicals, which would be absurd, as they are not admitted as radicals at all. Therefore these tests are unreliable.
In the second place, besides cyanogen, sulphur and a number of other elements combine readily with hydrogen, the bulk of which are not halogens, while in reference to the supposed analogy existing between hydrocyanic and hydrochloric acids, I really fail to see any grounds for this.
Hydrochloric acid is a very strong one, intensely acid, and forms salts with the alkaline metals which are quite neutral. Hydrocyanic acid on the other hand, if acid at all (which I doubt), is so feebly so that “it scarcely affects the blue litmus paper"; indeed I believe it to be neutral, as any minute acid reaction which has been obtained in respect to it may be due to carbonic acid, hydrocyanic acid being very prone to decompose with evolution of carbonic acid.
Further, in accord with this, the salts of cyanogen with the alkaline metals are not neutral, as are the corresponding salts of the chlorine group, but strongly alkaline.
In reference now to the third supposed joint characteristic of cyanogen and the radicals to which it is compared, we can parallel this in the case of sulphur and phosphorus; thus either of these elements, when warmed with a solution of any caustic alkali, forms oxygenated and haloidal salts, a part of them being oxidized at the expense of the oxygen of the alkali, as in the case of cyanogen, chlorine, etc., under these circumstances.
Lastly, as to the polar affinities of cyanogen and the crystalline form of its potassium salt. Sulphur and oxygen when liberated by voltaic action also
detach from the negative pole; while in reference to the similarity in the crystalline forms of cyanide of potassium to the chloride, so many substances crystallize in the same form, though these are of a widely different nature that, as a single test of position, form can be of little value.
Thus I think the grounds upon which we class cyanogen in this manner do not when carefully examined prove at all sound, but it rather appears, if admission to the group of halogens is given to cyanogen, that we must upon principle further admit within it substances, such as sulphur and oxygen, which obviously should not enter there.
But, outside anything yet stated, it is indisputable that the heavy metallic cyanides do not correspond in general with the chlorides, bromides, etc., of this series of metals; except in the case of the silver salts, there is no appearance even of harmony in this direction.
Again, the most stable oxygen compound of cyanogen is, according to the new chemical notation, Cy O, while that of chlorine is Cl2 O5, of bromine Br2 O5, etc; further Cy O (cyanic acid) forms compounds with the metals which are generally insoluble in water, alcohol, or ether; while chloric acid, its alleged analogue, generally forms compounds with them, possessing considerable solubility in these liquids. There is in fact as great a difference between the two acids and their metallic compounds on these points as there is between carbonic and nitric acid and between their respective metallic compounds; further, the composition of platino-chloride of potassium is K + Pt + Cl4, while that of the platino-cyanide is K4 + Pt2 + Cy10, exhibiting again a marked difference.
The great dissimilarity existing between cyanogen and the elements of the chlorine group, analogically considered, being thus shown, and the ground I hope consequently ready for the reception of a better classification than the one attacked, I now proceed to show what I conceive to be the proper position of cyanogen in regard to the elements. For this purpose I will refer you to the supposed points of resemblance between this substance and chlorine, which I have just criticised, and I think you will find that, wherever the true character of cyanogen is correctly stated, it agrees precisely with that of oxygen.
Thus, to recapitulate a little, oxygen, especially when in the allotropic form, combines directly with metals generally, including gold and silver, moreover it combines with hydrogen to form a neutral compound, and this when electrolyzed delivers its oxygen at the positive pole. Besides this cyanogen resembles oxygen, wherein, as shown, it differs from the chlorine group, its compound with the alkaline metals being caustic, and those with the heavy metals characterized by great insolubility in water, while several of these cyanides are soluble in alkaline cyanides, precisely as several of the
metallic oxides are soluble in alkaline oxides; further, cyanogen, like oxygen, is capable of assuming an allotropic condition.
Following up analogies here, I would class cyanogen and sulphur together, and so I would their hydrides. Hs, like cyanogen, is not strongly acid, indeed probably not acid at all, for as in the case of hydrocyanic acid Hs exhibits a great tendency to oxidize when in cóntact with water and to form oxyacids, so that in testing this gas for acidity we are liable to obtain reactions not due to the gas itself.
Our new nomenclature, by doubling the equivalents of oxygen and sulphur, has disturbed the uniformity which before this existed between their common hydrides and that of cyanogen; thus one point of resemblance has been removed, but I think this has been done somewhat arbitrarily in regard to cyanogen. Certainly when the equivalent of cyanogen is retained, its hydride then being Cy H (hydrocyanic acid), comparing with that of chlorine, the supposed similarity of these substances is maintained; and this by the way may have been one of the reasons for which the doubling process described was broken off at cyanogen. However, if I am correct in assuming that this compound is analogous with oxygen rather than with chlorine, its equivalent will also require doubling. If you now agree with me, or at least will contemplate the possibility that cyanogen is not analogous to chlorine and its isomorphs, but rather to oxygen, you will be in a position to perceive certain interesting relations which it bears to oxygen, and which could not well have presented themselves had the assumption I have here attempted to disprove remained unassailed.
Thus ferro- and ferri-cyanogen become upon this view ferri-oxides in which oxygen is replaced by its isomer cyanogen, and the same being true for the rest of the metallic cyanides, these substances should be, I think, viewed as comparing with the oxides of sulphur and chromium as they exist in the sulphates or chromates; further, sulphocyanogen and selenocyanogen, the only compounds containing cyanogen (or at least its elements), which do compare with the simple halogens, are not at all analogous with cyanogen. The cyanides thus viewed are not salts at all any more than the oxides are; sulphocyanides on the other hand are true salts, comparing exactly with the corresponding salts of the halogens.
Further, in regard to the question often raised as to the nature of certain of our elements, whether compound or not, it seems interesting that in this compound, cyanogen, we have a substance very similar to the element oxygen, one which at least only varies from it within the limits we are compelled to allow for variation in the members of certain well defined natural groups of our elements. We are thus, as far as is allowable from such apparent resemblances, justified in entertaining the supposition that oxygen itself is
also a compound body. I need not remind you in this connection that any theory which touches upon the nature of this gas has now an especial interest to us, for as you will be aware this and our most common gases or gaseous vapours are, for good reasons, considered to be distributed throughout the earths and suns generally, * and even to pervade the spaces between them and to perform all the functions we have hitherto allotted to a purely hypothetical substance. The nature therefore of any gas which is possibly a constituent of that which we now consider to be a universal atmosphere, becomes invested with an importance to us far beyond what we could even conceive of a short time since.
Lastly, in regard to the question as to the nature of our elements, it appears a very noteworthy circumstance that, by combining cyanogen with sulphur, which is also an analogue of oxygen, we obtain a compound analogous to the halogens I have referred to. That this ternary compound sulphocyanogen should be thus a true salt-radical, is strongly favourable to the idea that one or more of the chlorine group of elements is of a compound nature, and in relation to this it is worthy of record that, as I have already pointed out, the “equivalent number of sulphycyanogen is one which is very nearly the mean between that of chlorine and bromine.”
However, whether these facts indicate anything of this kind or not, I think the object of this paper has been fulfilled, for I believe I have shown that, to use a familiar but significant phrase, cyanogen has not the “stuff” in it for making a salt-radical singlehanded, therefore it is not in any way analogous to one, but in order to make it so we must combine it with another element, so that three elements in place of two are as yet the smallest number required to form a compound salt-radical.
In concluding my paper, I cannot avoid expressing a wish that the question which I have raised here had been taken up by some one more accustomed, by training and association, than myself, to grapple it by the aid of what is well termed the “New Chemistry.” I have worked at this question by the old lights; but if by this I am successful in inducing any one to take it up who will work at it by the new ones, I shall be satisfied with the result.
[Footnote] * Fuel of the Sun, by W. Mattieu Williams, F.C.S.