CYANIC ACID (from Gk. edavoc, kyanos, dark-blue). An unstable compound of carbon, hydrogen, oxygen, and nitrogen, obtained by heating eyanuric acid (q.v.) in a current of car bon dioxide. Under ordinary conditions it is a volatile liquid having a strong pungent odor, but is readily transformed into a white, porcelain like mass of the same percentage composition as cyanic acid. though probably of much higher molecular weight. This polymeric modification of cyanic acid is known as eyamelide. (See \\MILER.) Among the salts of cyanic acid may be mentioned the cyanate of potassium and the eyanate of ammonium. Potassium eyanate may he readily obtained by cautiously heating a mix ture of potassium ferrocyanide and potassium hichromate; when pure it forms a white crystal line powder readily soluble in water, in which, however, it gradually undergoes decomposition. Ammonium eyanate may be obtained from the cyanate of potassium by double decomposition. The transformation of ammonium cyanate into urea, observed by W;hler in Ig•S. constituted the first synthesis of an organic compound and formed an event of the greatest importance in the history of chemistry.
The careful study to which many derivatives of cyanic acid have been subjected has led to the view that cyanic acid may possess two different constitutional formulas, viz. N E C —0-11 and = C = N— Ii. All efforts to produce two dif ferent compounds corresponding to those formu las having failed, chemists have proposed to ex plain this comparatively rare pbenQnmeuou on the following hypotheses: ( I ) Cyanic acid, like most other organic compounds, has a definite structure—say N = C-0-11; but while, dur ing sonic of its transformations, that structure re mains unaltered, other transformations involve an intra-molecular change resulting in the forma tion of derivatives of the compound 0 = C = N —II (iso-cyanic acid'), which is, fur some un known reason, less stable than the compound N E C-0-11 and incapable of existing in the free state. (2) According to another hypothesis,
every single molecule of the acid is constantly changing its structure, its hydrogen atom rap idly oscillating between the nitrogen and the oxygen; so that while at a given instant the structure of the molecule might be represented by the formula NE C-0-11. we would find its structure to be 0 = C = N — H if we could stop the motion of the hydrogen atom at the very next instant. The substance is thus imagined to be composed, at any instant, of two different kinds of molecules; and as under certain conditions each kind may be capable of transformations which the other kind could not undergo, two series of derivatives should be expected. accord ing to the nature of the transformations neces sary to produce those derivatives and to the conditions under which the transformations take place.