may be effected by mixing the solution with a solution of nitrate of silver. A precipitate will be formed, which, after washing and drying, may be exposed to heat in a small glass retort; a gas will be given off, which as it is soluble in water must be collected over mercury. It may also be obtained from the crystals of a similar saline body known by the name of deuto-cyanide of mercury, the formation of which, from animal matters, will be hereafter explained. § 508. Upon exposing these crystals to a moderate heat, they first give off water of crystallization, and fall into a gray powder. When this anhydrous cyanide of mercury is exposed to a red heat in a glass retort, it turns to deep brown colour, metallic mercury distils over, and a gaseous compound is given off which may be collected over mercury. When generated in a confined space, it liquefies at a pressure of between three or four atmospheres at the temperature of 45°. The liquid is colourless and limpid, and, when relieved from pressure, speedily evaporates with the production of intense cold. The gas is colourless, and has a penetrating, very peculiar smell. When a lighted taper is dipped into a jar containing it, it is immediately extinguished, but the gas itself burns in the air with a beautiful purple flame edged with blue, which is very characteristic. 100 cubic inches weigh 55.5 grains. It sustains the application of a high heat without undergoing decomposition. Water dissolves about 4 times, and alcohol 23 times its bulk of this gas. It may be detonated with oxygen; and its analysis may be effected in this way, or by passing it over red-hot oxide of copper. One volume mixed with two of oxygen, and fired by the electric spark, afford exactly two volumes of carbonic acid and one volume of nitrogen. Whence it appears to be a compound of two equivalents of carbon and one of nitrogen. According to the principles of the scientific nomenclature, its name would be bi-carburet of nitrogen: but it is more frequently denominated cyanogen, from its entering into the composition of a blue compound with iron, to be hereafter noticed. The result of its analysis by oxygen is thus represented in symbols; C2N +40= 2 CON § 509. The brown matter which is left in the retort after the decomposition of cyanide of mercury, is also a compound of carbon and nitrogen in exactly the same proportions; and we have here a curious and important fact with regard to chemical combination, brought for the first time under our notice; namely, that compounds may be formed of the same elements, in the same proportions to each other, which may yet differ essentially both in their physical and chemical properties. The facts regarding such a constitution of bodies are grouped together under the term isomerism; and such compounds are said to be isomeric with their analogues: we shall have occasion to describe several such compounds in the progress of our inquiry, and we shall find them chiefly amongst the combinations of carbon. We are led from such facts to conclude, that a definite, specific, condensation, approximation, or arrangement in space, of the constituent particles of a compound is no less essential to its individual constitution than a certain proportion between its heterogeneous ingredients. The nature of such a variety of composition is clearly revealed by the difference between the equivalents of the isomeric bodies in entering into combination with other bodies, and by the volume which they occupy as gases, compared with the volumes of the elements of which they consist. The isomeric compound of cyanogen is also formed when a solution of cyanogen in alcohol is left to time, and is sometimes produced in charring animal substances. It has been called para-cyanogen. When heated in the air, part of the carbon burns away, and a residue is obtained which consists of one equivalent of carbon and one of nitrogen, which may be denominated the proto-carburet of nitrogen. § 510. A more intimate acquaintance with the primary compounds of carbon has lately discovered to the view of chemists a mode of secondary combination, which appears to be very different from that of acids with bases. It seems to be almost peculiar to this Proteus of the elementary substances, and its development is of the utmost consequence to a clear understanding of organic compounds, of which carbon constitutes the basis. Its first illustration may be best taken from the combinations of cyanogen. § 511. Cyanogen is neither acid nor alkaline in its nature, and it has little disposition to enter into combination with metallic oxides; but it has a remarkable tendency to combine with elementary substances in a manner perfectly analogous to that of the simple gaseous substances which we have been examining. When potassium, for example, is heated in cyanogen gas, the metal combines with the gas with great energy, and becomes incandescent. The saline mass which results must obviously be a ternary compound of carbon, nitrogen, and potassium: or 2 C,N,Ka; but it may be more advantageously regarded as a binary compound of cyanogen and the metal, or C,N,Ka. Similar compounds may be formed with all the metals, and from their analogy to the class of oxides they are denominated cyanides. The deutocyanides of mercury and silver, which we described as the source from which cyanogenmay be procured, are also instances of this binary combi nation. § 512. It also forms compounds with the non-metallic elements, which are of high importance and interest, inasmuch as they are of an acid quality, and are capable of entering into secondary combination with the bases. We will illustrate this by shortly examining its combination with hydrogen, but the more complete examination of its compounds must be reserved till we come to treat of organic chemistry. Binary Compounds of Cyanogen. § 513. The compound of cyanogen and hydrogen cannot be obtained by the direct action of the two substances, but may be formed by double elective affinity, by passing some of the compounds of hydrogen over deutocyanide of mercury. Such a compound may be obtained by acting upon a combination of sulphur and iron with dilute sulphuric acid, in which case, instead of pure hydrogen, a definite compound of hydrogen and sulphur is evolved, which we shall hereafter examine. By passing a current of this gas over the deutocyanide of mercury in a horizontal glass tube, double decomposition ensues; the sulphur combines with the metal, and the cyanogen with the hydrogen; and the latter compound, being very volatile is easily driven over by a gentle heat into a cooled receiver placed for its reception. It is a colourless liquid of a strong pungent odour, something resembling, when diluted, that of peach-blossoms. Its taste is said to be acrid; but it is so extremely poisonous, that a drop falling upon the arm of a man has been known to occasion death. Great care should be taken not to inhale its vapour. It is extremely volatile, and generates so much cold during its evaporation that a drop placed upon a piece of glass will spontaneously freeze. It boils at a temperature of 80°. Its vapour takes fire upon the approach of flame, and when mixed with oxygen, may be detonated by the electric spark. It feebly reddens litmus paper. Its specific gravity at 45° is 0.705, and that of its vapour 0.947. § 514. Two volumes of the vapour require two volumes and a half of oxygen for their perfect combustion; and two volumes of carbonic acid, with one volume of nitrogen, and water, are the products. These results indicate two equivalents of carbon, one of hydrogen, and one of nitrogen, as the elements of the acid. When potassium is heated in this vapour, cyanide of potassium is formed, and hydrogen, equal to half the volume of the acid, is disengaged. It is therefore a compound of equal volumes of cyanogen and hydrogen. The results of the analysis may be thus stated: § 515. It is sometimes called Prussic acid as being derived from the Prussian blue; but the scientific nomenclature distinguishes the class of acids, into the composition of which hydrogen enters, by the prefix hydro,-and hence it is also called the hydro-cyanic acid. The symbolic representation of the results of its detonation with oxygen is as follows: HC,N + 50 = 2CO, HỌ, N The symbol of cyanogen is sometimes contracted into Cy. H,C2N = HCy § 516. Hydrocyanic acid forms a salt by combining with ammonia, in their respective equivalents 27 and 17: it crystallizes in cubes or small prisms, and is very volatile. It may be formed in abundance by passing ammonia over red-hot charcoal. The hydrocyanic acid also enters into combination with the oxygen bases; but the binary compound of cyanogen and the metal is the general result, as the hydrogen of the acid and the oxygen of the base are in exact proportion to form water together. Thus, cyanide of potassium is formed by neutralizing potassa with hydrocyanic acid, and when red oxide of mercury is shaken up with the same acid it loses its colour, and deutocyanide of mercury is found in solution. CyH, KO CyK, HO 2 CyH, HgO= Cy2Hg, 2 HO § 517. Cyanogen also generates three isomeric acids by combination with oxygen; but the process by which they may be formed and insulated from their combinations is circuitous. By exposing a mixture of peroxide of manganese and ferrocyanide of potassium (a salt which may be made by the action of potassa upon animal substances,) to a dull red heat, in an iron pot, and boiling the resulting compound in alcohol, another salt may be obtained in tabular crystals consisting of the acid in question, or cyanic acid, in combination with potassa, and which may therefore be distinguished by the name of cyanate of potassa. The explanation of these processes will be given hereafter. The acid may be transferred from the potassa to the oxides of lead, mercury, or silver, by double decomposition with the salts of those metals with which it forms insoluble compounds, and from these it may be disengaged by sulphuretted hydrogen, the sulphur of which combines with the metal, and the hydrogen with its oxygen. It is thus obtained as a sour liquid, smelling something like vinegar, and very prone to spontaneous decomposition. § 518. According to its analysis, the cyanic acid is a compound of one equivalent of cyanogen and one equivalent of oxygen, CN, O. It is readily converted into carbonate of ammonia, by merely boiling its solution, or that of any of its salts; a change which an attentive consideration of its symbol, in connexion with that of water, will readily explain; for one equivalent of cyanic acid, with three equivalents of water, are exactly equal to one equivalent of bicarbonate of ammonia: thus, Cyanic Acid. Water. Carb. Acid. Ammonia. |
