Azulmic acid is formed in large quantities together with ammonic oxalate by action of cyanogen on aqueous ammonia. On the other hand, by bringing together equal volumes of dry ammonia and cyanogen gases, they combine to form a black amorphous powder of the formula C,NH6, hydrazulmine: 2(C2N2) + 2NH3 = C1N6H6, which is rapidly converted into azulmic acid by action of water : C4N6H6+ H2O = C1N2H2O + NH3, the direct formation of the latter being represented by 2C2N2 + H2O + NH2 = C1N¿H2O. 3 5 If an aqueous solution of cyanogen be mixed with some acetic aldehyde, it is completely converted into oxamide : whilst in presence of strong mineral acids it is converted into oxalic acid: CEN + 4H2O + 2HCl = EN CO.OH + 2NH,Cl. This transformation shows most strikingly that the carbon atoms in dicyanogen are joined together, and also that oxalic acid is a true dicarbonide. There are indeed also other reactions known, by which the carbon atoms of dicyanogen are disunited, with formation of single cyanogen compounds; for instance, on passing dicyanogen through potassic hydrate, there is formed, besides potassic azulmate, considerable quantities of potassic cyanide and cyanate: C,N,+ 2KOH=KCN + KCNO + OH,; 2 ide on passing it over ignited potassic carbonate, potassic cyanate and isocyanate are formed: whilst potassium heated in cyanogen burns and forms potassic cyanide : 125. By the trivalent combination of the nitrogen to the carbon atoms, cyanogen appears as a double ammonia molecule, whose six hydrogen atoms are replaced by the hexavalent dicarbon group, C2. In consequence of this method of saturation of the nitrogen atoms, the cyanogen molecule is able (like hydrocyanic acid) to form compounds, which are analogous in many ways to ammonia derivatives. Especially noticeable amongst these are the compounds with hydric sulphide. When equal volumes of cyanogen and hydric sulphide are mixed together in glass vessels, the sides of the latter are soon covered with yellow crystals of cyanogen monosulphhydrate, C2N2H2S: By heating their aqueous solution with silver salts, the compound is decomposed with evolution of cyanogen and precipitation of argentic sulphide : H On passing cyanogen into a saturated solution of sulphuretted hydrogen until there is present one volume of the former to every two volumes of the latter, red needles of cyanogen disulphhydrate separate : which corresponds to a doubled ammonic sulphhydrate. They are difficultly soluble in cold water, more easily in alcohol and ether. The aqueous solution gives coloured precipitates with lead and silver salts: 126. Paracyanogen, CxNx, is, as already mentioned, a porous blackish substance left behind in the preparation of cyanogen gas from mercuric cyanide. It contains carbon and nitrogen only, and is polymeric to cyanogen. By strong ignition it is converted into cyanogen; by action of potassic hydrate it yields true potassic cyanate. GUANIDINE, CN3H5. 127. Guanidine is a body genetically related to the cyanogen amides, as it contains a carbon atom whose four bonds are saturated by nitrogen, being united to three atoms of the latter. Guanidine is carbondiamide-imide : NH, NH2 It was originally prepared by the decomposition of guanine (see this) by chlorine, but later also obtained in many other ways. It is obtained from chloropicrin and orthocarbonic ether by action of ammonia, and by heating urea or biuret (§ 137) in an atmosphere of hydrochloric acid. It is further obtained by action of an alcoholic cyanamide solution upon ammonic chloride at a temperature of 100°. According to the equation: the hydrochloride is first formed, soluble in water and alcohol, from which guanidine is separated by argentic oxide. It is also easily obtained as the hydrodide by heating cyanogen iodide with alcoholic ammonia to 100°: It forms colourless crystals, readily soluble in water and alcohol, of strong alkaline taste. It absorbs carbonic anhydride from the air, and forms therewith a salt crystallising in beautiful quadratic prisms, (CN3H5),H2CO3. Guanidine nitrate, CN3H5.HNO3, crystallises in colourless prisms, rather difficultly soluble in water. The hydrochloride yields with platinic chloride yellowish-red prisms, of the formula 2CN3H6C1,PtCl4, easily soluble in water, and hydrated alcohol, difficultly soluble in anhydrous alcohol; with auric chloride beautiful long, deep-yellow needles, CN3H6Cl, AuCl3, rather difficultly soluble in water. By heating with concentrated alkaline solutions, it is resolved into ammonia and carbonic acid : ΝΗ NH, + 2KOH + H2O = COK + 3NH3. NH 2 OK Similarly by action of strong acids under the influence of high temperatures: (CN2H3)2H2SO4 + 2H2SO4 + 4H20 = 3(NH4)2SO4 + 2CO2. DERIVATIVES OF CARBONIC ACID AND CARBONIC DISULPHIDE. 128. Carbon monoxide is the common radical of the carbonic acid derivatives, and, as such, is termed carboxyl; it forms a true unsaturated compound: C=0 which is capable of further direct combination with other elements. By union with oxygen it forms carbonic anhydride, Co; it unites with nascent chlorine, or with chlorine gas in sunlight, to form carbonic oxychloride, or phosgene gas: -Cl The latter compound, formerly only known in the gaseous state, has lately been obtained, by sufficient reduction of temperature, as a colourless liquid of specific gravity 1.432, and boiling at + 8°. The liquid is most readily obtained when chloroform (two parts) is heated with a mixture of potassic dichromate (five parts) and sulphuric acid (forty parts), and the evolved gases conducted through strongly cooled tubes. The properties and modes of preparation of the oxides and sulphides of carbon and of the metallic carbonates will not be referred to here, being fully described in works on inorganic chemistry. The amide derivatives of carboxyl require considerable notice. 129. Carbamic Acid.-The white powder, obtained by mixing ammonia with carbonic anhydride, in absence of water, formerly regarded as anhydrous ammonic carbonate, is the ammonic salt of carbamic acid: It is usually prepared by passing the two dry gases into absolute alcohol, from which it separates slowly in thin leafy crystals. It sublimes below 100°, and unites with water to form ammonic car bonate: CO.NHONH, + H,0=COONH4)2; from which it can in part be again obtained by sublimation : CO(ONH,),= H,O + CO.NHONH; so that the ammonic carbonate of commerce invariably contains small quantities of this salt. Carbamic acid, NH, cannot be obtained from its salts by action do он, of acids, carbonic anhydride and ammonia being formed. It is more stable in its ethers, i.e. those compounds which contain an alcohol residue, instead of the hydroxyl-hydrogen atoms, and which are termed urethanes; they will be found described under the respective alcohols. Carboxylimid, CN_H see pseudocyanic acid (§ 100). occurs in the urine of all animals, more especially of the mammalia, and amongst these in largest quantity in that of carnivora; also in other animal fluids, as in blood, the amniotic liquid, and the vitreous humour of the eyes of mammalia, &c., but normally in only small quantity. In animal bodies, it results from the retrograde metamorphosis of nitrogenous tissue, and also from the direct decomposition of nitrogenous food without previous conversion into animal tissue. It is separated from the blood by the kidneys, and leaves the body in the urine. On interruption of the secretion by the kidneys, its quantity increases in the blood and other animal fluids. It is prepared synthetically (together with other bodies) by action of ammonia upon carbonic oxychloride : COCl2 + 4NH3 = 2NH,Cl + CO(NH2)27 on carbonic ethers and urethanes. It is further formed from cyanamide on treatment with dilute nitric acid (§ 114), most easily by the transformation of ammonic cyanate (§ 103). This last method of preparation was discovered by Wöhler in 1828, and is historically important, as the first instance of an undoubtedly organic body being obtained by artificial means. Instead of preparing ammonic cyanate from cyanic acid and ammonia gas, and then transforming it into urea by repeated solution in water and evaporation, the aqueous solution of crude potassic pseudocyanate is decomposed by an equivalent quantity of ammonic sulphate: 2C<N-K + (NH4)2SO4 =20<N_NH + K2SO1. whereby, instead of ammonic pseudocyanate, urea is obtained: |