CXIV.--Ho2o Mercurous and Mercuric Scclls change into each other. By SEIHACHI HADA, B.Sc. (Japan). NOTWITHSTANDIKG the numerous investigat'ions of the change o€ mer- curous salts into mercuric and the converse, in the absence of oxidising or reducing agents, but little is known of the way in which these changes come about. The work recorded in this paper proves that in such cases all mercurous salts dissociate into mercury and mercuric salts ; and reciprocally, under similar conditions, a1 I mexxmic salts combine with mercury forming mercurous salts, a view held by Rose so strongly that he denied the existence of any precipitated basic mercurous salts, considering them as mixtures of mercuric basic salt with mercury. Dec3mposition of mercurous salts into mercury and mercuric salts increases with rise of temperature, and only progresses freely so long as the mercury set free is continuously removed from the field ; and, conversek, combination of mercuric salts with mercury only becomes complete in presence of excess of the metal and at lower tempera- tures, unless the mercurous salt, produced is insoluble, as in the case of the chloride.Dissociation of mercurous salts into mercury and mercuric salts in the presence of water is caused not only by an elevated temperature, but also by light, even at the ordinary temperature, and apparently in all salts. Further it will be shown that some mercurous salts are oxidisable by air in presence of water when the temperature is much above 100". It has been found also that mercui-ous nitrate becomes a mercuric salt spontaneously in presence of water.Moreover, either in a few hours at 150°, or at the ordinary temperature in strong daylight, a large fraction of the mercurous salt may become mercuric without separation of mercury, being converted into mercuric nitrite and nitrate, the traces of nitrous acid generated by the heat or light start- ing the action. Mercuiy Nitrates. Conversion of alereuric A7iitrate i d o Mercurous Nitrate.-Although Barfoed mentioned the fact that mercuric nitrate solution dissolves finely divided mercury (" The Behaviour of Mercurous Salts with Soda," in Danish, 1853, J . p r . Chem., lSSS), it does not appear to be known that a solution of mercuric nitrate shaken violently for a very short cime with large excess of mercury is eutirely converted into one of mercurous nitrate.This simple method of pi-eparhg a solution1668 HADA : HOW MEICCUROUS AND MERCURIC SALTS of mercurous nitrate free from nitrous acid has been in use in this laboratory for years. Stability oj' nlemirous Nitrate.-Before treating of the ways in which mercurous nitrate passes into mercuric nit rate, something has to be said as t o its stability. It is a matter of common observa- tion that mercurcus nitrate kept for some time becomes yellow; but this I find is not true of the carefully prepared salt. As Marignac pointed out (1849), the crystals usually enclose mother liquor, but if this is thoroughly removed from the crushed crystals by pressing them between filter paper and drying them in a desiccator, the salt is obtained in a stable condition.A solution of mercurous nitrate, free from nitrous acid and kept in a closed vessel, appears to be quite stable if kept in the dark. Well cleaned and effloresced mercurous nitrate, if kept in a bottle, bas always a peculiar ozone-like odour, Decomposition of Me?-curous Nityate h y Water.-Normal mercurous nitrate, carefully freed from acid mother liquor, is decomposed by water leaving basic mercurous nitrate. The statements in hand-books that the salt dissolves completely in a little warm water arises, no doubt, from its not having been freed from acid mother liquor. The precipitate of basic salt, even if kept for some hours in an open ve3sel under the mother liquor at or about looo, but not in a strong light, still remains essentially free from mercuric salt.Dissociation of Mei-curous Nitrate by Heat and by Light.-The dis- sociation of mercurous nitrate at the ordinary temperature in the absence of light, if it goes onat all, is so slight as to escape detection. About 1 gram of normal hydrated mercurous nitrate, free both from metallic mercury and from mercuric nitrate, and 10 C.C. of water were put into an Erlenmeyer flask furnished with a reflux condenser, and kept immersed in boiling water, a current of carbon dioxide being passed through the apparatus st) as to exclude air ; before very long a lustrous, very thin film of mercury could be seen in the lower part, of the condenser, which became a coating of globules in two hours, when the heating was stopped, The basic salts in the flask were the11 dissolved in a little very dilute nitric acid, their soliition being quickly poured off from the mercury and added t o the main quantity of solution.The mercury was weighed dong with that removed from the CoiTdenser, the mercuroiis salt in the solution precipitated as chlo- ride by sodium chloride, and the mercuric salt in the filtrate estimated as sulphide. The mercuric sulphide corresponded with 0.0378 gram of mercury, whilst that obtained as metal weighed 0.0392 gram, the two weights being the same within the limits of experimental error. A similar experiment was made, the solution being kept in gentleCHANGE INTO EACH OTHER. 1669 ebullition, but no carbon dioxide was passed through the apparatus, the steam of the boiling solution being relied on to keep out air.The mercury found as mercuric salt weighed, this time, 0.0913 gram, and that as metal 0.0946 gram. In a third experiment just enough nitric acid was added (included in the 10 c.c.) to keep all the mercurous salt in solution ; the mercury volatilised was 0.0345, and that present as mercuric nitrate 0*0415, the latter being probably not more than equivalent to the metallic mercury, if all had been collected, only 7 milligrams being wanted. Three parallel experiments were then made, the flasks being heated in boiling water during eight hours, carbon dioxide being passed through the first (I), and a gentle current of air through the other two (I1 and 111) ; just enough nitric acid to prevent the precipita- tion of basic salt> was added to the contents of the third flask (111).The results were (in grams) I. 11. 111. Metallic mercury . . . . . . 0.1191 0.1195 0.1104 Mercury as mercuric salt 0.1213 0.1202 0.1065 In these experiments, one-third of the mercurous nitrate had decomposed into mercuric nitrate and metal in I and 11, and nearly as much in 111, where nitric acid had been added. Further, no sensible oxidation of mercurous nitrate by air or nitric acid had taken place. Proust (1816) appears to have known that on boiling a solution of mercurous nitrate, mercury volatilised with the steam ; but the fact of t,he volatilisation of mercury appears in none of the modern chemi- cal dictionaries or hand-books. Rose's views (Annalen, 1841, 39, 106) have already been referred to; he is clear on the point that mercuroiis nitrate when continuously boiled with water becomes mer- curic nitrnte and mercury, but he thought that the insoluble salt formed when mercurous nitrate is treated with water contained both mercury and mercuric nitrate, which is not the case.Although it has not been experimentally proved that mercurous nitrate in cold solution is dissociated by the action of light, it may be mentioned that exposure to bright daylight soon darkens basic mercurous nitrate, as it lies under the mother liquor ; and a similar effect observed in the case of some other mercurous salts is certainly due to dissociation. Oxidation of Mercurous Nitrate by Oxygen at 150°.-Three experi- ments were made using 1 gram of mercurous nitrate in each case. In I this was heated at 1-50' for six hours, with water (10 c.c.), in a sealed tube, the air in which had been displaced by oxygen.Much of the oxygen was absorbed, and 6.5 per cent. of the mercurous nitrate converted into mercuric salt, this was partly in solution, partly VOL. LXIX. 5 u1670 HADA: HOW MERCUROUS AND MERCURIC SALsTS in the form of brilliant, yellow crystals of basic salt (mercurous and mercuric). Experiment I1 was the same as I, except that all the salt was in solution in nitric acid of 1 per cent. More than 28 per cent. of the mercurous salt became mercuric nitrate. Much oxygen was absorbed, but no nitric acid reduced. In 111, mercurous nitrate was heated at 150', with water only, for five hours, in an atmosphere of carbon dioxide. It underwent no change beyond slight dissociation, the dissociation in the sealed tube being impeded by the retention of the mercury vapour.In these experiments it is possible that the nitric acid may have acted to a small extent as a carrier of oxygen, but as other mercurous salts are also oxidisable at 150', this may be left out of consideration. Nercurous Nitrate not sensibly Oxidised by Air at Lower Tempera- tures.-As experiments made long ago by Mialhe have been accepted as establishing the oxidisability of wet mercurous chloride by air at only a slight elevation of temperature, a modification of his experi- ment was made in order to test the point in the case of mercurous nitrate. Three experiments were made as follows :-Two small flasks were employed ; one (A) of these being closed by a cork, whilst' the other (B) was provided with a reflux condenser and a tube to pass carbon dioxide through the solution.In I, the two flasks ( A and B) each containing 1.5 grams of mercurous nitrate, and 15 C.C. of water, were placed side by side in an oven, and heated for about 45 hours at a temperature OE 45-47', carbon dioxide being continually bubbled through the mixed solution and precipitate in one of the flasks. In IT, each flask contained 2 grams of mercurous nitrate, 20 C.C. of water, and st little dilute acid, the temperature being 45-50Oand the time 75 hours. Experiment 111 was like I1 except that the temperature was 20- 30' and the time 50 hours. The quantity of mercury sulphide obtained from the mercuric salt produced was determined in each experiment. The following are the results, A being the closed flask containing air, and B the one through which the carbon dioxide was passed.Mercuric A . * . . . . . . 0.0040 gram 0.0082 gram. sulphide { B . . . . . . 0.0107 ,, 1. 11. 0-0276 ,, I n Experiment I, the amount of mei*curic sulphide in B is Z$ times what it is in A, whilst in I1 it is nearly 3k times as great, In 111 the quantities of mercuric sulphide were too.small'to weigh, but the blacking produced by hydrogen sulphide in B was far greater thanCHANGE INTO EACH OTHER. 1671 in A. This effect is, no doubt, due to the current of inactive gas carrying off mercury vapour. Mercurous Nitrate changed by Heat and by Light to Me?.cun'c Salt by Redwtion of Nitric acid. Action of Heat.-In a sealed tube and in an atmosphere of carbon dioxide, 1 gram of mercurous nitrate, dissolved in 10 C.C. of one per cent.nitric acid, and kept at 150' for five hours, was found to be largely converted into mercuric salt, some of the nitric acid being reduced to nitrous acid. Action of Light.-One gram of mercurous nitrate dissolved in 10 C.C. of one per cent. nitric acid was put into each of a number of small Erlenmeyer flasks, some closely sealed, and others having the mouth covered with filter paper. Most, of these were exposed to strong daylight, the rest being kept in the dark; other flasks containing mercurous nitrate with water alone were also exposed to light. The contents of the flasks were examined at the expiration of 19 days and 33 days respectively. In every case where the flask had been exposed to light, much nitrous acid and mercuric salt had been formed, whilst those which had been kept, in the dark had suffered no change after 19 days, and even after 33 days the amount was insignificant, notwithstanding that the place where the flasks had been kept was far from being absolutely dark.In these closed flasks, the mercuric radicle was found to be half as great again in 33 days as in open one. Evidently, therefore, asrial oxidation plays no sensible part in the conversion of mercurous nitrate into mercuric nitrate. Oxygen would seem, indeed, to impede the conversion in the absence of basic salt, for, at the end of 19 days, the conversiDn t o mercuric salt was half as great again in a closed flask in which the air had been replaced by carbon dioxide, as it was in a closed flask containing air.On the otber hand, in a flask containing 2 grams of mercurous nitrate and 10 C.C. of water, there was found, at the end of 19 days, a quantity of mercuric radicle just, the sanie, whether the atmosphere were one of oxygen or of carbon dioxide; a similar result was obtained after 33 days' exposure in atmospheres of carbon dioxide and air respectively. Some of the flasks employed had each a bent tube of considerable diameter passing through the cork, and, at its outer end, dipping into a, vessel of mercury. The effect was striking where the experiment lasted for 33 days. Whether the atmosphere was air or carbon dioxide, the production of mercuric radicle was only two-thirds in this mercurial atmosphere of what it was in a non-mercurial atmosphere.Some- The influence of mercury vapour was also studied. 5 u 21672 HADA: HOW MERCUROUS AND MERCURIC SALTS what similar, but less marked, results were obtained where the exposure lasted only 19 days. The inhibitory effect of mercury vapour is the same as that of free exposure to the open air, the reason being that the nitrous acid, produced by the action of light SO slowly as it is, gets diffused away on exposure to air, or removed by the memuray vapour, and its accu- mulation impeded. It mnst be remembered that, in these sollations the amount of free nitrous acid present must always be very minute, a consideration which will explain the resemblance between the effect of the action of mercury vapour and that oE free exposure to air.Experiments of this kind must all be made together, differences in temperature and, above all, in the intensity of the daylight, having a marked effect. The numbers in the table are the quantities of mercury found as mercuric salt, 0.7143 gram being the tot'al mercury present in each flask (or twice that where 2 grams of mercurous nitrate were taken instead of 1 gram). The results are appended in a tabular form. With nitric acid : Open ................. Closed, air. ........... Closed, air, mercury.. .. Carbon dioxide ........ Carbon dioxide, mercury Oxygen". ............. Oxygen, in darkness . , . Oxygen, mercury". .... May 21st- June 23rd. 0.0377 0.0543 0.0363 0.0542 0.0383 0.0247 0.0181 0.0042 May 21st- July 3rd- June 9th. July 23rd.- - 0.0146 0,0368 0*0158 - 0.0240 - 0.0201 0.0285 0.0324 lost - 0~0000 - - Without nitric acid : Oxygen (2 grams salt to - 10 c.c.) ............. 0,0680 0.0222 Mercury Xukhates. Conversion of Mercuric to Mercurous Xu1phate.-It is well known that mercuric sulphate and mercury, when rubbed together and moistened with water or alcohol and a little sulphuric acid, combine readily, but the process, although of great theoretical importance, is not a convenient one for the preparation of pure mercurous sulphate. Decomposition of Mercurous Sulphate by Water.--It is familiar to every chemist that, whereas mercuric sulphnte turns bright yellow on contact with water, mercurous sulphate remains white, even when f The result8 obtained in oxygen are too marked to be relied on, and need con- 6:rmation ; one analysis wae spoiled.CHANGE INTO EACH OTHER.I673 trashed. When mercurous sulphate is precipitated from a solution of mercurous nitrate free from mercuric salt and nitrite, by adding to it dilute sulphuric acid, and then well washed, a white precipitate is obtained, bui, if this is well shaken twice successively with 1000 parts of distilled water, i t becomes of a clear, though light, yellow. Decomposition of Mercurous Xulphate by Light and hy Heat.--In the experiments just described, light must be excluded, as mer- curous sulphate, when moist, becomes dark brown in a strong light, and that which has become yellow by treatment with much water becomes first greenish, and then dark brown. It seems safe to assume that these colour chaDges are due to dissociation of the mercurous salt into mercuric salt and mercury or n hypomercurous salt.As the efl'ect is only superficial, it is too slight to admit of its nature being ascertained. When the sulphate is boiled with water for some hours, mercurous sulphate is converted, to a small extent, into basic mercuric sulphate, mercury, and sulphuric acid. The mercury was got as a sublimate, the water became acid, and the undissolved sulphate yielded some mercuric chloride when treated with hydrochloric acid. Oxidation of Mercurous Xulphnte a t 150°.-Heated for six hoars in oxygen, with water and a little sulphuric acid, in a sealed tube at 150°, 1 gram of mercurous sulphate gave no mercury, but 0.0121 gram mercuric radicle, indicating the oxidation of 1.5 per cent.of the mei-curous sulphate. Owing t o its insolubility, much of the sulphate is kept out of contact with the oxygen, and is not acted on, the same being t'rue of the phosphate and chloride. Rose observed the dissociation of mercurous sulpha.te by boiling it for a long time with much water. Mercwy Phosphates. Conremion qf Mercuric into Mercurous Phosphate.-Moist mercuric phosphate, tritmrated with its equivalent of mercury, unites with it, growing warm, and becomes mercurous phosphate, at all events for the most part. Moist mercurous phosphate is darkened by light. No attempt was made tJo decompose it by cold water. Dissociation of 2CIercurozis Phosphate by Beat.-Mercurous phos- phate was obtained by adding a solution of mercurous nitrate to a good excess of sodium phosphate solution acidified with nitric acid ; the precipitate was then washed and dried on a tile.When this salt is boiled for six hours, a small sublimate of mercury was obtained and the phosphate became pale yellow from the presence of basic salt ; the liquid was acid and contained both mercuric and mercurous phosphates dissolved in phosphoric acid, or as acid phosphates. Rose got very similar results, and Gerhardt observed thah mercurous1674 HADA: HOW MERCUROUS AND MERCURIC SALTS phosphate when heated dry is converted into mercuric phosphate and mercury. Oxidation of Mercurous Phosp7zate.-When heated at 150" in oxygen, mercurous phosphate was oxidised to much the same extent as the sulphate. Mercury Acetates. Conversion of Mercuyic into Mercuyous Acetate.-A cold dilute solution of mercuric acetate shaken violently with much mercury is readily and rapidly converted into mercurous acetate ; Lefort (Annalen, 1845, 56) states that it requires long boiling to effect the change, which is incorrect, as mercurous acetate dissociates easily.Dissociation of Mercurous Acetate by Heat and by Light.--It has long been known that mercurolis acetate yields a little mercury when its solution is boiled. Berthemot (1848) definitely states that mercurous acetate is partly decomposed by boiling water into mercury which separates and mercuric acetate which dissolves. I find that mercurous acetate dissociates so freely when boiled with water, that the mercury not only volatilises with the steam,but collects in globules under the solution.Both the portion of the salt which remains undissolved and also that which ci-ystallises out on cooling are mixtures of normal and basic mercurous acetates, the mother- liquor containing much mercuric acetate. The addition of acetic acid before boiling does not sensibly affect the dissociation, though it prevents the formation of basic salt. Vogel has stated that sugar boiled with mercurous acetate yields mercury, but I find that the presence or absence of cane sugar makes no difference. Comparative experiments made with 1 gram of mercurous acetate in 10 C.C. of water and in 10 C.C. of B strong sola- tion of sugar, raised to the boiling point and then cooled, gave 0.0627 gram and 0.0612 gram of mercuric sulphide respectively. It is known that mercurous acetate is very sensitive to light.Some exposed under water t o sunlight for four days, was strongly blackened, and the solution contained mercuric acetate. In a com- parative experiment where light was excluded, the mercurous acetate was scarcely changed in colour. Oxidatiow, of Mercurous Acetate.-When mercurous acetate is heated a t 150" with water and oxygen in a sealed tube for some hours, mnch of the oxygen is absorbed and mercuric acetate formed. Only a little of the metal separates. Mercury Perchlorates, Oxalu tes, and Caybonate. With regard to the perchlorates (see Chikashigk, Trans., 1895, 67, It is known that mercurous oxalate when heated at 100' 1013). changes partly into mercury and mercuric oxalate.CHANQE INTO EL4CH OTHER. 1675 The decomposition of mercurous carbonate is so intimately con- nected with that of the oxide, tihat it will be noticed in that con- nec tion.Mercury Chlorides. Conversion of Merczcric into Jferctwozcs ChloYide.-A solution of mercuric chloride, when shaken with a large excess of mercury, is quickly converted into mercurous chloride ; the conversion, how- ever, cannot be completed in the presence of much alkali chloride. This process is not, indeed, well adapted to the preparation of mercurous chloride, but' as a mode of its formation, is only second in scientific importance to the union of chlorine with mercury. Dissociation of Mercurous Chloride by Heat.-The experiments on the dissociation o f mercurous chloride were carried out in a manner closely resembling those made on the nitrate. 1 gram o f freshly precipitated mercurous chloride in 10 C.C.water was heated in a flask immersed in boiling water ; it gave a sublimate of mercury in the coudensei* tube, and mercuric chloride was found in the solution. The results are given in the table. I n Experiment I, a current of sir was passed during the time of heating which was 7 hours. In 11, a current of carbon dioxide was used insbead of one of air, whilst in Experiment 111, a little hydrochloric acid was added to the water, and a current of air was used, the time of heating being 8 hours. I n Experiments IV and V, n dilute solution of potassium chloride was used instead of water. In IV, air was passed, and in V, carbon dioxide, the heating being 6 hours in both cases. The effect of the potassium cb loride on the dissociation was marked.I. 11. 111. IV. v. sublimed .. .. . . . . 0.08 0.08 0.1305 0.1763 0.16 salt . . . . . , . . . . . . . 0.0983 0*1008 0.1307 0.1923 0.1823 Metallic mercury Mercury as mercuric In all these experiments minute globules of mercury were visibly mixed with the mercurous chloride, accounting for the deficiency in weight of the sublimed mercury. The results of the carbon dioxide experiments show that little? if any, oxidation could have occurred in the air experiments. Xerczcrous Chloride not changed by Boililzg Water except that it slowly disappears as Mercury and Hercuric Chloride.--If shaded from day- light and contained in a porcelain or hard glass vessel, mercurous chloride may be boiled with distilled water, as long as any of it remains, without suffering any change in appearance or composition.Simon and Ginboch both noticed that when mercurous chloride is1676 HADA: HOW MERCUROUS AND MERCUHIO SALTS boiled with water in an open vessel, it disappears very slowly, the undissolved portion consisting of unaltered mercurous chloride. Notwithstanding statements to t'he contrary, there is no evidence whatever that in the decomposition of mercurous chloride into mer- curic chloride which takes place when it is boiled with dilute hydro- chloric acid, any oxidation takes place, dissociation fully accounting for all the facts observed. i\iIialhB found that mercurous chloride gave more mercuric chloride in an open vessel than in one which was closed; this was, no doubt, due t o the fact that dissociation could proceed in the former case, whereas the retention of the mercury vapour in the closed vessel stopped it, as is shown by what follows.Mercurous Chloride not seiasibly Oxidised at Lower Temperatures.- MialhB's experiments were repeated with the crucial modification of using a current of carbon dioxide instead of air, the method being precisely like that employed in the case of mercurous nitrate (p. 1670). The two flasks were heated at about 50' for 45 hours. The result was less marked than in the case of the nitrate, the mercuric chloride produced being exceedingly small in quantity. The water from the flask through which carbon dioxide had been passed gave a marked hlackening with hydrogen sulphide, whilst that which contained air and had been kept closed, gave only a moderate browning.This confirms MialhB's results, in so far as i t shows that much more mer- curic salt is produced in a current of gas than in a closed space. Oxidation of Jlercurous Chloride at 150°.-Although mercurous chloride is not sensibly oxidised by air at temperatures as high as 100' at least, it is readily oxidised at 150"; when heated with water for six hours in an atmosphere of carbon dioxide, in a sealed tube, there was scarcely any change, dissociation being hindered by the retention of the niercury vapour. Using a 3.7 per cent. solution of hydrochloric acid and a 6.5 per cent. solution of potassium chlor- ide instead of water, there wits a small amount of dissociation into mercury aud mercuric salt.Very different were the results when the air of the tube had been displaced by oxygen before sealing ; the amount of metallic mercury under these circumstances W R S very small, but much mercuric salt was formed. When water alone was used, and the heating lasted six hcurs, the mercuric chloride was found partly in solu- tion, and partly as brown, brilliant, micaceous scales of oxychloride. When the water contained hydrochloric acid in one case and potas- sium chloride in another, in the proportions given abow, all the mer- curic salt was found in the solution. In all cases there had been a large absorption of the oxygen. In presence of hydrochloric acid, using 1 gram of mercurous chloride, as much as 47.5 per cent. became mercuric chloride, whilst in the potassium chloride solutionCHASGE INTO EACH OTHER.1677 it was 19 per cent. ; in the latter experiment the solution was strongly alkaline. I n another experiment, where it was heated with 50 C.C. of the 3.7 per cent. of hydrochloric acid during 10 hours, 60 per cent. of the mercurous chloride was changed into mercuric chloride. I n the potassium chloride experiment, there was more dissociation than when hjdrochloric acid was used, as shown by the greater sepa- ration of mercurg . Memury Bromides a d Iodides. No new experiments upon the bromides and iodides seemed called for, it having becn proved that mercurous bromide dissociates in h o t solutions of alkali bromides, and mercurous iodide decomposes in solution of potassium iodide, also that the latter may be formed by rubbing mercury and mercuric iodidc together.i3Ierciwous Oxide and Carbonate. It has long been known that mercurous oxide decomposes nwre or less a t t,he common temperature into mercuric oxide and mercury, and i n 2883 Barfoed proved that the black substance produced by the action of alkalis on mercurous salts is, a t first, real mercurous oxide for the most part, although almost a t the moment of its production, it contains metallic mercury and, therefore, mercuric oxide. When freely exposed to the air, metallic mercury volntilises, the mercurous oxide also gradually disappears, and, finally, nothing but mercuric oxide remains, the mezwmous oxide, no doubt, continuing to decom- pose into mercury and mercuric oxide. I made two experiments by exposing mercurous oxide in cold, dry weather to the air, i n open vessels.The average increase in weight per diem was (1)-0*025 per cent., and (2) 0.023 per cent. ; this rate of increase, which represented the joint, effect of gain of oxygen and loss of mercury, though not very regular, did not become less towards the end of the exposure than it was on the first days. In a third experiment the oxide was spread orer it glass dish, after it was thoroughly dry. I n a desiccator it decreased in weight, but only 0.001 per cent. in 13 days, which seenis to prove that dry mei-curous oxide does not oxidise in dry air. The same portion was then exposed freely to cold, dry air for 14 days, during which time it lost in weight a t the rate of 0.004 per cent. per diem, as t'he combined result of loss of mercury and gain of oxygen.The oxidation of mercurous oxide is, therefore, a very slow proccss. So far as can be ascertained, this oxide is the only mercury compound t'hat does oxiclise a t the common temperature, or even a t 100'. Aferczcrozu carbonate is formed when moist mercurous oxide is1678 MERCUROUS AXD JIERCURIC SALTS. exposed to carbon dioxide gas (Barfoed). I n the air it slowly decom- poses into carbon dioxide, mercury, and mercuric oxide. Noit-existence of ikIerczcrous S!( Zphide. English authorities agree in stating that when mercurous nitrate is added to excess of hydrogen sulphide, it yields mercurous snlphide, which begins at once to decompose, yielding a mixture of mercurous and mercuric sulphides, with metallic mercury. Continental writers generally have accepted Barfoed's experiments, showing that hydro- gen sulphide at once converts a mercurous salh into mercury and mercuric sulphide, and therefore that mercurous sulphide has no existence.* I find that if the black precipitate produced by hydrogen sulphide in mercurous nitrate solution is digested with cold, nitric acid, itl quickly begins to whiten, being converted into mercuric-sulphide- nitrate. Moi-eover, if the moist precipitake is washed on a filter several times successively with small quantities of nitric acid of sp. gr. 1.2, the mercury cannot be completely separated from the mercuric sulphide. The freshly prepared black precipitate is quickly acted on by a solution of mercuric nitrate, the products being mercurous nitrate and mercuric-sulpliide-nitrate. But although the two cornponenh of the mixture cannot be quantitatively separated, the fact remains that mercury and mercuric sulphide together behave just as does the supposed mercurous snlphide. Thus, cold nitric acid, sp. gr. 1.2, does uot, by it8self, convert precipitated mercuric salphide into the white sulphide nitrate; but does so if some mercury is present, It is known, too, that mercuric sulphide i s whitened by digestion with a solution of mercuric nitrate. For particularsof early work on the subject of this paper, Gmelin's Handbook may be consulted. In conclusion, 31 wish to record gratefully my indebtedness to Dr. Edward Divers for his guidance in carrying out this research. Iwpwial University, !116kyii, JapaN. * The author appears to have overlooked the paper by Antony and Sestini (Gnzaettn, 24, i, 193), an abstract of which is to be found i n the 8ociefy'a Journttl (Abstr., 1894, ij, 318). - [EDITOR.]