consequently, which the lowest temperatures tend to produce. Ferrosum changes readily to ferricum (iron of peroxide). This property corresponds to that presented in chemistry by pyrophoric iron and protoxide. It furnishes in this way steel and malleable iron; but, when not arrived at the condition of blistered iron, it retains under these two forms the power, always well determined, of being changed, by the usual metallurgic reactions, from iron to steel and from steel to white crystalline cast-iron. The physical characteristics of ferrosum when combined with carbon, are hardness and fragility. From its chemical properties it should be ranked among the bodies which combine with a single atom of oxygen. Ferricum is the metal of anhydrous peroxide ores. Its metallic type is the iron produced from these ores. It unites with carbon at high temperatures, but the latter is deposited during slow cooling for want of affinity. This condition corresponds to the high temperatures, like that of welding heat. It gives malleable iron, and as a variation of form, blistered iron; but when alone it cannot pass to the state of steel any more than to white cast-iron-at least, by means of the short reactions which can be effected in metallurgy. This almost absolute impossibility of reverting to the state of ferrosum, except, indeed, with great difficulty and in a very unstable manner, after having existed in the ore in the state of ferricum, corresponds, moreover, to the difficulties in the way of the chemical reduction of peroxide. Its physical characteristic is the malleability which it loses only on attaining its ultimate form-blistered iron. Its chemical properties cause it to be classed among the bodies which combine with at least three atoms of oxygen, and more of an odd number. Black and grey cast-irons are not physical conditions determined by a collection of identical molecules. They are simply ferricum, preserving a part of its properties, and depositing when slowly cooled the carbon with which the reaction had charged it while hot. In grey cast-iron ferricum is generally predominant; in mottled cast-iron the two irons are present with their characteristics; ferrosum gives the white portions and the carbon combined; ferricum gives the grey portions with a carbon deposit. Malleable irons are formed of mixtures in varying proportions of two irons of different origin, both in the state of ferricum. Ferrosum in this state always partially preserves its hardness and power of returning to its original form, as I have already described. The variety found in the irons of commerce depends on the number of mixtures possible. The magnetic oxide ores contain the two irons in atomic proportions. These ores give the most stable and perfect steels; hence it may be concluded that stee is produced by the reunion of two conditions of iron, and that it is nearest perfection when it holds the two irons in a closer relation than that which exists in the ores. It is not necessary to consider steel as a new state, for magnetic oxide is formed merely of a combination of two oxides. The correctness of this definition of steel may be proved by a very easy experiment: a mixture of soft or blistered iron (ferricum) and white cast-iron (ferrosum) operated on before or after fusion, always gives when in right proportions a more or less perfect steel recognisable by tempering. It must, moreover, be observed that magnetic oxide of iron and magnetic pyrites possess, like tempered steel, permanent magnetism. This property, common to both natural and artificial loadstones, independent of the state of oxide, of sulphide, or of carbide, must then result from the simultaneous presence of two allotropic conditions of iron, which is the only constitutive element common to these very different bodies. The two allotropic conditions of iron, proceeding from the two oxides, are then present in metallurgy, with a similar system of variations; but they are rendered distinct by a certain number of properties. Besides which, they may go through most of the metallurgic reductions and transformations, without losing their original characteristics, or being confounded one with another. These phenomena present the most complete analogy with the well-known properties of the two tartaric acids, distinguished by the direction in which they deviate from the plane of polarisation. The study of the calorific capacities of various products furnishes results which prove, between crystalline cast-iron and certain malleable irons, numerical differences too important to be explained by the presence of foreign bodies. I hope that the examination of these calorific capabilities, together with a very simple mode of assay, may furnish a practical process for determining the nature and origin of the irons contained in all the products; their use and value may thus be ascertained. It is, moreover, very desirable that there should be a process for testing the qualities to prevent not only intentional fraud, but also those mistakes which may be committed in the present state of metallurgy. Verifications of the new principles which I have laid down are to be found in the explanation of even the most obscure phenomena; a series of verifications which I will succinctly indicate, after having made known the laws regulating the action of heat and of reagents in the metallurgy of iron. PROCEEDINGS OF SOCIETIES. COLLEGE OF PHYSICIANS. LECTURE 6. Uric acid-Its excretion throughout the animal kingdom — History of its chemical examination—Its undecomposibility save by oxidation-Classification of uric acid products into an-ureides, mon-ureides, and di-ureides-Also into carbonic, oxalic, and mesoxalic compounds-Oxidation of mesoxalic into oxalic, and of oxalic into carbonic acidUreides formed by an elimination of either one or two atoms of water—Table of uric acid products—Additional intermediate and amidated bodies-Oxalic mon-ureides and di-ureides-Mesoxalic mon-ureides associated with barbituric acid-Mesoxalic di-ureides, including hypoxanthine, xanthine, and uric acid-Their mutual convertibility-Relationship of xanthine to guanine-The pseudo-uric and urozanic acids-Uric acid viewed simply as a compound of carbonic oxide and urea-Tissue metamorphosis affected by alterative medicines Activity of loosely combined oxygen-Nitric oxide as a carrier of active oxygen-Comparison between nitric oxide and iodine as oxygenants— Resemblances and differences between iodine and chlorine -Free chlorine more active than iodine, and free iodine more mobile than chlorine-Alterative action of iodine dependent on its chemical mobility-Similar characters of arsenic, mercury, &c.—Effect of alkalies on tissueoxidation-Conclusion. Of all the incompletely oxidised products of tissue-meta- tively simple molecules; that hippuric acid, for instance, morphosis, uric acid is, I suppose, the most important, whether regarded from a physiological and pathological, or from a purely chemical point of view. In combination, chiefly with ammonia, it forms the principal urinary con stituent voided by insects, land reptiles, and birds. Normally, it occurs but in small proportion in the urine of man, while it is found in yet smaller proportion in that of carnivorous, and can scarcely be said to exist-if, indeed, it does habitually exist-in that of herbiverous and omniverous quadrupeds. According to various authorities, it is to be found constantly in the juices of the human spleen, liver, lungs, and brain. The merest traces of it are also met with normally in blood, but its proportion therein under certain forms of disease, such as albuminuria, and more especially in gout, becomes very appreciable. In certain cases of gout, indeed, all the fluids of the body are more or less saturated with uric acid, and some of them even supersaturated, so as to deposit those wellknown concretions of urate of sodium, commonly called chalkstones. I need scarcely refer also to the frequent excess of uric acid discharged from the human kidneys, under greater or less derangements of bodily health, and to its deposition in the form of urinary sediment, gravel, or calculus. As shown by its formula, C,NHO, uric acid consists of only sixteen elementary atoms, and is consequently, as regards its ultimate composition, a far more simple body than many of those we have previously considered. Nevertheless, the problem of its intimate constitution for a long time baffled all attempts at solution, and cannot, even at the present day, be considered as quite satisfactorily unravelled. Uric acid was discovered in 1776 by the renowned Swedish chemist, Scheele; but it was first submitted to a minute investigation by Liebig and Wöhler, whose efforts resulted in the production and identification among other new bodies of alloxantine, alloxanic acid, dialuric acid, uramile, mesoxalic acid, allantoine, mycomelic acid, parabanic acid, &c., and whose admirable work, published in 1838, forms the broad and sound basis of all our subsequent knowledge. These chemists had been preceded by Brugnatelli and Prout,-the discoverers of alloxan and murexide respectively-and were succeeded more particularly by Schlieper, Pelouze, Fritzsche, Gregory, and IIlasiwetz. To the number of bodies already described, Schlieper added the leucoturic, allituric, dilituric, hydantoic, hydurilic, and allanturic or lantanuric acids, the last also discovered by Pelouze. In 1853, Gerhardt, in his celebrated "Traité de Chemie," gave a very complete account of the then known uric acid products, and, by dividing them into two well-defined natural groups, simplified very greatly the knowledge of their origins and metamorphoses. Among subsequent workers, Baeyer has increased the list of compounds by his discovery of pseudo-uric acid, hydantoine, violantine, and the violuric and barbituric acids, the last-named being a body of very great interest, and has also thrown consider able light upon the nature of the compounds previously discovered by Schlieper. Moreover, adopting Gerhardt's classification as a basis, and viewing both old and new products from the extreme height of modern doctrine, he has published by far the most complete and connected account of the uric acid group of compounds which has hitherto been given to the world. The scheme which I am about to bring under your notice, and which is, I think I may say, even more comprehensive, does not differ greatly from that of Baeyer in general conception, and is indebted very largely to him for its elaboration. I propose, however, to differ from him in disregarding altogether the molecular arrangement of the different compounds, preferring to limit myself in this, as in previous lectures, simply to questions of origin and relationship. I have already told you that the great majority of complex organic bodies are built up of the residues of compara is constituted of the residues of benzoic acid and glycocine, while tyrosine is constituted of the residues of salicic acid and ethylamine,—the glycocine and ethylamine themselves containing residues of ammonia and of glycolic acid and alcohol respectively. Now, uric acid is evidently built up in a similar manner, and contains the residues of several constituent molecules. But a hitherto insuperable difficulty in determining its exact mode of construction arises from the circumstance of its never having been decomposed into the actual molecules of which its constituent residues are the representatives, but only into the oxidised, or, rather, dehydrogenised, products of these molecules. Add to uric acid an atom of oxygen, so as to burn off two of its atoms of hydrogen, and it breaks up with the greatest ease, though without this additional oxygen it has hitherto proved undecomposible. You will observe from its formula, C,NHO,, that uric acid contains five atoms of carbon and four atoms of nitrogen, while urea, CN,H10, contains only one atom of carbon and two atoms of nitrogen. Accordingly, we find that when dehydrogenised uric acid undergoes complete decomposition by an absorption of water, it breaks up into two molecules of urea (containing C,N) and one molecule of a non-nitrogenous 3-carbon acid. Whether, however, the residues of these two molecules of urea, obtainable by the oxidation or dehydrogenation of uric acid, pre-exist in uric acid, the 3-carbon acid alone being the dehydrogenised product, or whether the residue of the resulting 3-carbon acid preexists in uric acid, the two atoms of urea being produced by dehydrogenation, there is no evidence to show. The great stability of uric acid under treatment with even strong acids and alkalies is certainly opposed to its containing pre-formed residues of urea, since in all undoubtedly so constituted bodies the residues of urea are removeable or decomposible with the greatest facility. On the other hand, the assumption of pre-existent urea-residues in uric acid very greatly facilitates our conception of its decompositions, and, receiving the general consent of chemists, may, I think, be provisionally admitted by us on the present occasion. Be this as it may, when uric acid is subjected to an oxidising agent in presence of water, it gives up two of its atoms of hydrogen to the oxidising agent, while the dehydrogenised product reacts with water to form mesoxalic acid and urea. Employing chlorine as the oxidising agent, we have the following reaction: Uric acid. Water. Chlorine. Mesoxalic. Urea Chlorhydric. C,NHO,+4H2O + Cl2 = C2H2O ̧+2CN2H2O + 2HC1; or, supposing the reaction with water to take place after the removal of the hydrogen by chlorine, NEWS ingly bear to uric acid the same relation that mesoxalic acid and alloxan bear to dehyd-uric acid, thus : Tartronic. Dialuric. C1N2HO Uric Acid. C3N2H2O3; C2H2O and, just as our hypothetical dehyd-uric acid yields mesoxalic acid and alloxan, so should actual uric acid yield tartronic acid and dialuric acid. In reality, however, these bodies have not been obtained by the mere breaking up of uric acid, but only by rehydrogenising the mesoxalic acid and alloxan which result from the breaking up of dehydrogenised uric acid. Despite, however, this flaw in the demonstration, we may provisionally, as I have said, regard the dialuric and uric acids as tartron-ureide and tartron-diureide respectively. The several bodies I have just mentioned are typical of three well-defined classes of compounds, to one or other of which the immense number of uric acid products are, with but very few exceptions, assignable. We have first the class of simple non-nitrogenous acids, or an-ureides, like the tartronic and mesoxalic acids. Then we have the class of bodies containing a residue of the acid plus one residue of urea, or the mon-ureides, such as dialuric acid and alloxan; and lastly, we have the class of bodies containing a residue of the acid plus two residues of urea, or the di-ureides, such as uric acid itself. Confining our present attention to the an ureides, let us consider briefly their derivation and mutual relationship. Mesoxalic acid, then, the most complex non-nitrogenous product obtainable directly from uric acid, constitutes the third term in the following series : = Oxalic. Mesoxalic. Oxygen. Carb-anhyd. C2H2O + Ö CO, + C,H,O Hence when uric acid is subjected to a more active oxidation than suffices to produce mesoxalic acid, we obtain oxalic acid, which may occur in its simple an-ureide state, or congregated with one atom of urea to form a mon-ureide such as parabanic acid, or congregated with two atoms of urea to form a diureide, such as mycomelic acid, a body having exactly the same relation to oxalic acid that uric has to mesoxalic acid. Now, just as we can convert mesoxalic into oxalic acid by burning off its excess of carbonic oxide, so may we convert oxalic acid itself into carbonic acid by a precisely similar oxidation, thus :— Oxalic. = Oxygen. Carb-anhyd. Carbonic. C2H2O + Ö CO2+ CH2O3. The rapidity with which the oxidation of oxalic acid can take place is easily capable of experimental illustration. In this tall beaker, for instance, I will place some ordinary black oxide or peroxide of manganese MnO2, a compound which readily parts with one of its two atoms of oxygen to become converted into protoxide of manganese MnO; while in the flask I will place an ounce or so of commercial oxalic acid. Now, upon drenching the acid with hot water and pouring the mixture of solution and crystals upon the oxide of manganese, we get, you perceive, a most rapid oxidation of the oxalic acid, accompanied by a violent effervescence of carb-anhydride which we shall be able to recognise in a minute or two by its high specific gravity and by its power of extinguishing flame and of rendering limewater turbid. The effervescence is at first so great as to be almost unmanageable, and a very slight agitation would cause the liquid contents to froth over the beaker, but now that the action is a little moderated I may prove to you the nature of the gas evolved by pouring some of it on to a lighted taper, which you see is immediately extinguished, and by pouring some more of it on this clear lime-water, which by agitation there with is immediately converted into an opaque mixture of chalk and water. Accordingly, when uric acid is subjected to a more powerful oxidation than suffices to produce oxalic acid, we obtain carbonic acid, which like the oxalic and mesoxalic acids is also capable of colligation with urea. No ureide of carbonic acid, indeed, has yet been obtained directly from uric acid, the active treatment which effects the complete oxidation of the uric acid effecting also a separation from one another of the resulting carbonic acid and urea, which, however, may be obtained in combination by other means. Allophanic acid, for instance, is a well known artificial mon-ureide of carbonic acid, but so far as I am aware no di-ureide of the acid has been hitherto produced by any process whatsoever. The mon-ureide of mesoxalic acid, of which I have already spoken-namely, alloxan, is formed from mesoxalate of urea by an elimination of two atoms of water; but there is another ureide-namely, alloxanic acid, which differs from the original salt by the loss of only one atom of water. Similarly oxalic acid forms two mon-ureidesnamely, parabanic acid or paraban analogous to alloxan, and oxaluric analogous to alloxanic acid. Carbonic acid, however, forms but a single ureide, which is produced by the elimination of only one atom of water, and accordingly belongs to the same series as the oxaluric and alloxanic acids, thus: Acids. Ureides. CH2O, Carbonic { C2N2HO, Allophanic. C,H,O, Mesoxalic (CNHO Alloxan. CN,HO, Alloxanic. Similarly among the di-ureides, some are formed from their corresponding mon-ureides by an elimination of one atom, and others by an elimination of two atoms of water. Now, mesoxalic acid is convertible by deoxidation or hydrogenation into tartronic acid, as I have already observed; and by pushing the deoxidation a stage further we obtain malonic acid, both of them capable of forming mon-ureides and di-ureides; and in a similar manner the oxalic and carbonic acids furnish a variety of similarly behaving deoxidation products. When we consider, then, the total number of carbonic or 1-carbon, of oxalic or 2-carbon, and of mesoxalic or 3-carbon, hydrogenised products; and that the majority of these products, like their original acids, are capable of forming mon-ureides by an elimination of one atom, and other mon-ureides by an elimination of two atoms of water; and, further, that many of these mon-ureides are capable of forming di-ureides by a further elimination of one atom and other di-ureides by a further elimination of two atoms of water, we are no longer surprised at the great number and variety of known compounds belonging to the uric acid group, and shall not be surprised at the dis overy of very many more. The most important of those already known are included in the following table. It is divided perpendicularly into three columns of an-ureides, mon-ureides, and di-ureides; and perpendicularly into three layers of carbonic, oxalic, and mesoxalic products. The compounds connected by means of dotted lines differ in composition from one another by an excess or deficit of one atom of urea minus one atom of water; while those standing on the same level in the adjoining columns and unconnected by dotted lines, differ from one another by an excess or deficit of one atom of urea minus two atoms of water. NEWS 99 CNHO, Glycoluril CNHO Allantoine CNHO, Mycomelic CH2O, Glyoxalic CH2O Oxalic Mesoxalic Even this table, however, is far from being complete. Thus, I have introduced only one alcoholic urea as a type -namely, the methylic, excluding its homologues. I have also omitted uroxanic acid and several amidated and nitrocompounds, to which I shall presently refer. Moreover, between some of the consecutive mon-ureides shown in the table there exist certain diameric bodies formed by the union of the two consecutive mon-ureides with elimination of water. Thus, allituric acid is a diamerone of hydantoine and allanturic acid, while leucoturic acid is a diamerone of allanturic acid and oxaluric or parabanic acid, thus: Of the many bodies above formulated, only a few call for any special remark. Hydantoic acid is also known as glycoluric acid, which is, perhaps, a better name for it. Again, the body here called allanturic acid is probably identical with the lantanuric acid of Pelouze, and also with difluan. Oxaluric acid is interesting from the alleged occurrence of its calcium salt in human urine, in the form of the dumb-bell crystals so often associated with the octahedral crystals of oxalate. That these dumb-bells may consist of oxalurate of calcium, as suggested by their discoverer, Golding Bird, is not indeed improbable; but the evidence that they really are so constituted is anything but satisfactory. The relations of allanturic and oxaluric acids to another uric acid product known as oxaluramide are obviously those of hydrogen and water to ammonia, as illustrated in the case of so many other compounds, thus:H.H Hydrogen C,N2H2HO ̧ Allanturic. H.HO Water C2NH,(HO)O, Oxaluric. H.H2N Ammonia C2N,H,(H,N)O, Oxaluramide. Allantoine, as shown by the fine specimen lent me by Messrs. Hopkins and Williams, is a beautiful crystalline body existing in the allantoic fluid of the foetal and in the urine of the sucking calf. It has also been noticed by Frerichs and Städeler in the urine of two dogs, upon whose lungs they had been experimenting, and is very easily procurable from uric acid by oxidation with peroxide of lead. By deoxidation, it yields glycoluril (Rheineck). : As I have before observed, it stands to paraban in exactly the same relation that uric acid stands to alloxan. From the observations of Hlasiwetz it seems probable that some supposed urate of ammonia deposits occurring in urine really consist of mycomelic acid, which similarly evolves ammonia when treated with alkalies, and yields murexide when evaporated with nitric acid. Of mesoxalic mon-ureides, alloxan and barbituric acid seem to be the most important. Alloxan, the first discovered product of the artificial oxidation of uric acid, has recently been recognised by Liebig as a pre-formed constituent of urine. By treatment with bromine, it yields bibromobarbituric acid, which is successively convertible by hydrogenation into the bromobarbituric and barbituric acids, which last serves as a sort of nucleus in the following series of compounds : The last compound on the list—namely, violantineseems to be not a diamerone or residuary, but a completed compound of the violuric and dilituric acids. It is observable that the mutual relationship of barbituric acid, dialuric acid, and uramile in this sub-group is strictly parallel to that of allanturic acid, oxaluric acid, and oxaluramide in the preceding one. Moreover, the malonic and barbituric acids are homologous with the oxalic and parabanic acids respectively, or the most oxidised of known 2-carbon uric acid products are homologically the representatives of the least oxidised 3-carbon products, thusC2H2O, Oxalic C,N,H2O, Parabanic 4 CHO, Malonic CN.HO, Barbituric, although from another point of view they correspond more nearly with mesoxalic acid and alloxan, as I have already remarked. The relationship subsisting between the three mesoxaldiureides, though long suspected from the similarity of their formula-hypoxanthine C,N,H,O, xanthine CNHO,, and uric acid C,N,H,O,-has but very recently received an NEWS Xanthine. Parabanic. Guanine. Úrea. CN2H2(HO) + CO2 ? Para banic. Guanidine. CN2H ̧(H2N) +CO2. experimental demonstration at the hands of Strecker and Rheineck. With the first of these bodies, or hypoxanthine, originally found by Scheerer in human and bovine splenic juices, the sarcine, subsequently discovered by Strecker in juice of flesh, and thought to be a distinct base, has since proved to be identical. From the results of Scheerer, Strecker, Gorup-Besanez, and others, it appears that hypoxanthine exists to a very appreciable extent in most Moreover, xanthine itself occurs in small quantity as a glandular juices and in muscular tissue, particularly of secondary product of the above oxidation of guanine, and the heart, while it has also been recognised in brain sub-probably might be obtained in larger quantity by treating stance and in the blood and urine. It occurs as a white guanine with nitrous acid, according to the general method crystalline powder, insoluble in cold and sparingly soluble adopted for converting amidated into hydrated bodies, in hot water. By oxidation with nitric acid, it yields thus:xanthine, and hence gives the characteristic nitric acid re action of xanthine, which compound has also been detected in blood and in most animal juices. Under the name of xanthic oxide, it was discovered in 1819 by the elder Marcet in a variety of urinary calculus, which subsequent experience has proved to be very rare. It has been met with more frequently, indeed, though still very seldom, as an amorphous urinary deposit, and in one case recorded by Bence Jones it occured in lozenge-shaped crystals. Its habitual presence, however, in small quantity as a dissolved constituent of urine seems now to be very well established. Xanthine, moreover, is not only known as a urinary, but also as an intestinal concretion, for Göbel has met with it as the chief constituent of certain oriental bezoar stones obtained from ruminating animals. I have already referred to Strecker's artificial production of xanthine by the oxidation of hypoxanthine or sarcine with nitric acid. Conversely, Strecker and Rheineck have very recently shown that uric acid by deoxidation with sodiumamalgam yields a mixture of xanthine and hypoxanthine, the latter in greatest proportion, so that the actual rela tionship of these three bodies is now placed beyond all question. Hitherto, hypoxanthine and xanthine, having been obtained in small quantities only, have not been subjected to any detailed examination. It can scarcely be doubted, however, that xanthine is a mon-ureide of barbituric and a di-ureide of malonic acid, in the same sense that uric acid is a mon-ureide of dialuric and a di-ureide of tartronic acid. We may hope, indeed, to have these relations very soon established by experiment; for even if it should not prove possible to prepare xanthine advantageously from uric acid, still the fact of its close relationship therewith would lead us to expect its more abundant existence than has been hitherto imagined; particularly, for instance, in the excreta of those animals whose normal mode of tissue waste results in the production of uric acid rather than urea. This expectation is strengthened by the extraction from that valuable dried excrement of sea-fowl known as guano of a feeble base called guanine, which bears to xanthine the same often-referred-to relation that ammonia bears to water, as shown in the following series of formulæ : C,N,H,O. CNH (NO)O C,N,H,(H,N)O CN H2(HO)20 Just, in fact, as uric acid, and doubtless xanthine, yields by oxidation parabanic acid and urea, so does guanine yield by oxidation parabanic acid and amido-urea or guanidine, thus : * By the oxidation of kreatine, which has been already described as a polymerone of glycolic acid, methylamine, and urea, its glycolic residue is converted into oxalic acid, while its methylamine and urea residues are left in combination to form methylamido-urea or methyluramine, a compound homologous with amido-urea or guanidine, thus: Guanine. Nitrous. Xanthine. C,N ̧H ̧(H ̧N)O + (HO)NO = C ̧Ñ ̧H2(HO)O+N2+ H2O ? That the guanine extracted from guano is a constituent of the birds' excrement as voided, and not a product of decomposition, is rendered probable by its occurrence under other circumstances. Thus it forms the chief portion of the excrement of the garden spider, has been recognised by Scheerer in the pancreas of the horse, and is occasionally met with in human urine. We have now only left for consideration the pseudouric and uroxanic acids, which we may regard as terms in the following series : CN H, O, CN_HO + H,O=CN.H O CNHO2+ 2H2O CNH OS C ̧Ñ‚H2O2+3H2O – C ̧Ñ‚H1O C2N1H2O2+4H2O = Uric. Pseudo-uric. Unknown. Uroxanic. CHO, Tartronic+2CN,H,O Urea, Pseudo-uric acid is a recent discovery of Baeyer's. It has not actually been produced by the direct or indirect hydration of uric acid, but only by the combination of cyanic acid vapour with uramile. Just, in fact, as cyanic acid converts ammonia into anomalous cyanate of ammonia or urea, so does it convert the residue of ammonia contained in uramile into a residue of urea, so as to change the amido-monureide into a simple diureide, thus :Uramile. Cyanic acid. C ̧N2HÎ(NH2)0 ̧+CNHO = C1N2H3(CN2H3O)O3 = Pseudo-uric. C1N.H2O.. Pseudo-uric acid occurs as a white crystalline almost insoluble powder. Hitherto it has not proved dehydrateable into uric acid; but by dehydrogenisation in presence of water it behaves like uric acid, breaking up into alloxan and urea. The compound C,N,H,O, is unknown, while uroxanic acid, C,NH10O6, is known but very imperfectly. Unlike pseudo-uric acid, it really results from the absorption of water by uric acid, and is produced in the form of its potassium salt by boiling_uric acid for a long time in solution of caustic potash. In the free state it occurs as a white, glistening, sparingly soluble powder. The absorption of a fourth atom of water by uric acid would probably lead, not to the formation of a new hydrate, but to the breaking up of the uric acid itself, possibly into tartronic and urea. I have already referred to upwards of forty uric acid products, by no means all that are known, and I have indicated the existence of many more, as yet unknown, to fill up gaps in the different series. Now, when we reflect that in all probability most of these compounds, actual and problematical, do not stand alone, but are associated each with a more or less numerous set of isomers,—that is to say, of bodies having the same ultimate composition, but a different molecular arrangement-we scarcely venture to contemplate the almost overwhelming intricacy with which we are threatened. To us, as physicians, however, the subject is capable of assuming a simpler aspect. On any view of its constitution, hydrated uric acid differs in composition from two atoms of urea by the addition of three atoms of carbonic oxide, capable of oxidation into |