LECTURES ON ORGANIC CHEMISTRY:
GENTLEMEN,-As I promised, at the conclusion of my last lecture, we now proceed to describe the nature and properties of uranzile. URAMILE. This substance may be procured directly from the thionurates, more particularly from thionurate of ammonia. Concentrated sulphuric acid, when made to act, cold, upon any of the thionurates, causes the evolution of the sulphurous acid contained in them. But if a cold saturated solution of thionurate of ammonia is mixed with hydrochloric acid, or with dilute
... d, or with dilute sulphuric acid, and the mixture heated until it becomes slightly turbid, the sulphurous acid changes into sulphuric acid, at the expense of the oxygen contained in the organic substance with which it is combined in thionurate of ammonia, and the reduced matter to which, as I have already informed you, the name of uramile has been assigned, crystallizes, upon cooling, in the shape of plumiform, congregated, thin, hard needles, which effloresce when exposed to the air, or to a high temperature, and become converted into a rose-coloured powder. This substance is almost entirely insoluble in cold, and but little soluble in boiling water, but it dissolves unaltered in cold ammonia, and in cold solutions of caustic alkalies, and is re-ohtained from such solutions by the action of acids. However, if an ammoniacal or alkaline solution of uramile be allowed to stand in the air, it will assume a deep-purple tint, and, after the lapse of some time, there will then separate from the fluid those gold-green crystals of metallic lustre which I have had repeatedly occasion to mention in the course of the last three or four lectures. These crystals may likewise be procured from uramile, by boiling this substance with readily-reducible metallic oxides-such, for instance, as oxide of silver, or oxide of mercury. Uramile dissolves, likewise, in concentrated sulphuric acid, and is precipitated again from such solution, by water. By boiling with concentrated solution of potass, it becomes converted into uramilic acid, with evolution of ammonia. Strong nitric acid transforms uramile into alloxan, with the evolution of nitrous acid. The analysis of uramile gives us the following formula :-Cs Ns Hs 06 This formula explains, most satisfactorily, its mode of formation, as well as the transformations which it undergoes. Uramile is thionuric acid from which the elements of two equivalents of salphuric acid have separated-This also enables us to understand the transformation of alloxantine into uramile, by ammonia, or ammoniacal salts, with the simultaneous reproduction of alloxan. If we admit the existence of the hypothetical body of which I have spoken-namely, urilic acid, and trace its relation to uramile, we must consider the latter substance as a combination of urilic acid and ammonia, and consequently, as a compound, having a constitution exactly similar to uric acid, which, you will remember, is, upon this hypothesis, urilate (cyan-oxalate)of urea. Oxaluric acid, is uric acid in which the urilic acid has been replaced by o.1:alic acid: and uramile we must, according to this view respecting the constitution and relation of those substances, consider as a uric acid, in which ammonia has replaced urea. All this will become quite clear to you, if you will examine the fol-lowing table.-This view of the matter further enables us to understand the transformation of uramile into alloxan, by the action of nitric acid. This transformation differs but little from that which uric acid undergoes under the same circumstances. It is true, we may assume that oxidation of urilates takes place in both cases, and we obtain, in both cases, the same product of the oxidation of urilic acid-viz., alloxan ; but, in the one instance, the separated base combines unaltered with the nitric acid; whilst, in the other, the base (urea) is decomposed, together with the simultaneously evolved nitrous acid, into carbonic acid, nitrogen, and ammonia. URAMILIC ACID. I have alluded to a metamorphosis which uramile undergoes upon boiling with potass ley-viz., its transformation into uramilic acid. The continued action of dilute acids upon uramile causes the same transformation. But the best method of procuring uramilic acid is to mix a saturated solution of thionurate of ammonia with some sulphuric acid, and evaporate the mixture slowly in a water bath. After the lapse of some time, uramilic acid will separate in transparent prisms of a glassy lustre. These crystals of uramilic acid are soluble in from six to eight parts of cold, and in three parts of boiling water. The solution possesses an acid reaction. Uramilic acid forms crystalline soluble salts with the fixed alkaiies, and with ammonia. The solution of these salts, when mixed with lime or barytes compounds, produces white precipitates, which are soluble in large proportions of water. The analysis of uramilic acid gives the following as its formula :-C16 N5 Hm 0" According to this formula, uramilic acid is formed from two equivalents of uramile, by the separation of one equivalent of ammonia and the accession of three equivalents of water. Again: uramilic acid, when brought into contact with other substances, undergoes a series of metamorphoses, some of which present appearances highly remarkable, as you will subsequently have occasion to observe, but these metamorphoses of uramilic acid have not yet been examined. MUREXIDE. At the commencement of this series of lectures on the metamorphoses of uric acid, I had occasion to allude to an interesting observation of Dr. Prout. This chemist found, that when a solution of uric acid in nitric acid, after having been concentrated to a certain degree by evaporation, is supersaturated with ammonia, it assumes a purple-colour, deposits, after the lapse of some time, goll-greeii crystals, of a metallic lustre, to which he assigned the name of purpurate of ammonia. The name murexide has, however, subsequently been assigned to this substance, for reasons which I shall immediately have occasion to explain to you. We have already seen, in the course of these lectures on uric acid, that crystals of murexide are formed in various ways. But although murexide has so many various ways of formation, yet its production in a separate state for examination, is beset with considerable difficulties, since its instability requires the adoption of a great many precautionary measures in the process, which must be strictly attended to, to ensure the success of the operation. It is therefore advisable to prepare only small quantities of this substance at a time. One of the most common methods of preparing murexide is to intermix alloxan and alloxantin, to heat the fluid to about 158°, and then to add carbonate of ammonia. The carbonic acid escapes, the fluid turns purple, and after the lapse of some time deposits crystals of murexide. These crystals are obtained to perfection when solution of alloxan is kept boiling until part of it is transformed into alloxantin and parabanic acid, and ammonia is then added. In this case the fluid assumes a deep-purple tint, and deposits magnificent crystals of murexide. The mother liquor contains oxalurate of ammonia, which owes its origin to the metamorphosis of parabanic acid in contact with ammonia.