22 WRIGHT AND MENKE ON NAXGANESE DIOXIDE. IV.-ATotes on Naizganese Dioxide. By C. R. ALDER WRIGHT D.Sc. (Lond.) Lecturer on Chemistry in St. illIary’s Hospital Medical School; and A. E. MEXKE Daniell’s Scholar King’s College. § 1. Introductoyg. THE experiments described in this paper are essezltiallly a continuation of some observations detailed in the “ Second Report on some Points in Chemical Dynamics,’’ presented to the Society by one of us and Mr. A. P. Luff (this Journal 1878 1 504) in which it was shown that pure hydrated maxiganese dioxide is not produced by two of the processes nsnally described as giving rise to that substance viz., acting on potassium permanganate with nitric acid and treatment of manganese chloride with sodium hypobromite ; the products con-tained considerably less “ available oxygen ” than corresponds with the formula Mn02.These results have since been extended and con-firmed by Gorgeu (Cow@. re72d. 88 796) who has observed that the products obtained by oxidising protoxide or carbonate of man-ganese either heated or in the cold by treating manganate or per-manganate of potassium with nitric acid by exposing permanganic acid to spontaneous decomposition and by electrolysing dilute solu-tions of manganese salts uniformly contain less oxygen than corre-ponds to the dioxide. Various specimens of these products showed on titration amounts of total oxygen of from 35.2 to 36.5 per 100 parts of anhydrous substance MnO containing 36.8 parts hence the deficiency in the “ available oxygen ” amounted to from 0.3 to 1% out of 18.4 or from 2% to ik of the quantity of available oxygen in Mn02.These products were stable in the air or in contact with distilled * This was shown by a large number of experiments made by Tliudichuxn in con-junction with the author but unfortunately the manuscript was mislaid and so thc experiments hare not been published JJ-RIGHT AND MENlGC ON MANGANESE DIOXIDE. 28 water suffering no change even after lengthened periods of time ; on treating them with potash they neutralised and combined with amounw varying from 1 to 14 per cent. i e . they acted like feeble acids as Gorgeu had previously (in 1862) found manganese dioxide to be capable of doing (Aim. Chim. Plzys. [S] 66 153) forming salts of the general formula 5Mn02.X20 where X is a monad.On the other hand Gorgeu has also found that the manganese dioxide produced by heating manganese nitrate to about 160° shows little or no deficieney in oxygen and that it does not combine with potash exhibiting in these respects and in its physical properties a close resemblance to the natural minerals polinnite and pyrolusite. S. U. Pickering also has recently found that by dissolving manp-nese superoxides in large bulks of strong hydrochloric acid and diluting with water substances are precipitated which exhibit a con-siderable deficiency in available oxygen as compared with MnO (this Journal 1879 !€'ro.~~s. 654). During the last twelve months having had occasion to prepare a quantity of manganese dioxide for the purpose of examining the character of the curvd surfaces rcpresenting the mutual relations of time temperature and amount of deoxidation by various reducing agents we have examined afresh the product of the action of nitric acid 011 potassium permwanate and have been surprised to find that even when the quantity of nitrie acid present is very large relatively to the manganese the substance precipitated invariably contains a not inconsiderable amount of potassium combined so firmly as not to be in the slightest degree washed out by continued boiling with water.This circumstance bas led us to examine the substances regarded as more or less pure manganese dioxide formed artificially in various ways, with a view to seeing whether potassium is similarly retained by these substances when prepared in presence of potassium compounds.Our experiments indicate that whenever potassium is present in a solu-tion from which a manganese superoxide is precipitated a larger or smaller quantity is invariably retained in Combination in the precipi-tate. 'The same remarks appear as far as our experiments have gone, to be equally true as regards calcium and probably many other metals; indeed in the case of calcium the tendency of manganese dioxide to carry down foreign metals in combination appears to be superior to its power of uniting similarly with potassium for man-ganese dioxide precipitated from a solution conta,ining a little calcium, and several times as much potassium will frequently carry d,own more calcium than potassium. The action of nitric acid on pernianganate of potassium may be regarded from several points of view thus the action may be supposed t o consist in the setting free of permanganic acid which graduall 24 WRIGHT AND MENKE ON MANGANESE DIOXIDE.decomposes evolving oxygen and depositing manganese dioxide or manganese nitrate may be supposed to be formed and to react on the undecomposed permanganate in accordance with the well-known reac-tions (as applied to the sulphate or chloride) on which Gujard founded his volumetric method of manganese determinatioii :-3MnX2 + 2KMn04 + 2Hz0 = 5Mn0 + 2KX + 4HX. I n either case the retention of potassium in the precipitate seems to indicate that manganese dioxide (the acide manganeux of Gorgeu) is sufficiently acid in its character to displace nitric acid from nitrates.It is however difficult to see why the precipitate thrown down should exhibit a deficiency in oxygen for being formed in presence of excess of permanganate it should contain all tlhe manganese as dioxide, Gorgeu having stated in 1862 that when a manganous salt is added to excess of permanganate the precipitate has the coniposition of hydrated MnO, although a " manganite of manganese," 5Mn02Mn0 (or Mn6011, exhibiting a deficiency of one-sixth of the available oxygen in MnO?) is obtained when the permanganate is added to excess of the manganese salt (AWL Chirn. Pliys. [3] 66,153). Guyard subsequently stated whilst describing his volumetric method (Bzcll. SOC. ClLirn. 1864 1 SS) that the temperature of the solution influences the nature of tthe precipitate.At SO" a precipitate of hydrated Mn02 is thrown down ; at lower tem-peratures oxides exhibiting a deficiency of oxygen are obtained corre-sponding with the formulae 4Mn0.Mn207 and 5MnO.MnzO7 (or Mn6011. and Mn7Ol2) manganese dioxide prepared in this way beiug viewed by Guyard as a basic permanganate of manganese 3Mn0.Mnz07 and these compounds as yet more basic analogous substances. Guyard represents the precipitate as containing the elements of the hydrate MnO2.HZO ; Rammelsberg however (Ber. 1875 233) represents the substance formed by acting on potassium permanganate solution with strong sulphuric acid and then adding water as 3MnO?.2H2O,* and this formula is also applied by Morawski and Sting1 t,o the substance examined by them some months ago obtained by adding manganous chloride to potassium permangsnnte solution and drying over sulphuric acid ( J .pr. Chem [Z] 18 78). No one of these observerat appears to have noticed the presence of * Rammelsberg gives the percentages Mn = 55.56 0 = 16'16 caIculated for the iormula 3Mn02 2H10 and Mn = 55.48 0 = 15.63 as those found thus exhibiting a slight deficiency in oxygen to the amount of - 32 p r t doubtless, however the manganese was over-estimated a5 potash is carried down tlie preci-pitate. Vide s 4. j- Since the majority of our experimenis were mode a paper has appeared by J. Volhard (Annaleiz September 1879 198 318) in which tlie author states that the manganese dioxide precipitate obtained by adding poi assinm permanganate to 16.16 -15'63 - 1 - 16.1 WRIGHT AND MENKE ON JIAT\'GAI?\'ESE DIOXIDE.25 considerable amounts of potassium in these products (several per cents. of K,O). Morawski and Sting1 indicate in one part of their paper that the product obtained by the action of potassium permanganate on manganese chloride is free from potassium for they give the analytical numbers 56.0 per cent. of Mn and 1.33 of H (calculated for 3Mn0.2H20 Mn = 55.56 H = 1.34). Subsequently however they state that traces of potassium are apparently carried down with the precipitate as the filtrate contains ratlier more hydrochloric acid and rather less potassium than corresponds to the above equation; they indicate the amount however as being a t most only a few tenths per cent. inasmuch as they state that on treating this precipitate with potas-sium carbonate solution an amount of pota,ssiurn was withdrawn from ?he solution t o the extent of 9-17 and 9.23 per cent.the compound hjln,KH,O, (or 8Mn02.Kz0.3H20) being produced ; the calculated xmuunt for the tmnsformation of 3Mu02.2H20 into this compound is 9-87 per cent. This ultimate compound Mn4KH3010 they state is formed whenever potassium permanganate acts in a neutral solution (originally) upon various organic substances siich as potassium thio-cyanate alcohol glycerin oxalic acid &c. On repeating their experi-ments as described below we have obtained entirely different results, the alleged definite substance Mn4KH,010 not having been produced in any one instance examined. § 2. 2CZccngnnese Dioxide prepared from Potassium Perrriaiigannte by Nitric Acid A concentrated solution of potassium permanganate (filtered warm through glass wool) was acidulated with about one-fifth of its bulk of strong nitric acid so that the resulting liquid contained a t least 25 per cent.by weight of HNO, and kept on the water-bath for some time until most but by no means all of the permanganate was destroyed ; the heavy black precipitate was washed several times by decantation and tinally on a glass wool pnmp-filter until every trace of acid was absent from the filtrate. The product was then dried over sulphuric acid for several days; when dry to the touch the clots were pulverised by light pressure and the whole left over sulphuric acid for some months. Portions taken out after 1 3 and 5 months' standing over sulphuric acid were analysed with the following results.The available oxjgen was determined by boiling with hydrochloric acid receiving the evolved chlorine in potassium iodide solution and titrating with an excess of sodium thiosulphate going back with a decinormal iodine solution, manganese sulphate contains combined potassium unless the solution is strongly acidu-lated with nitric acid in which case not more than traces are present in the precipi-tate. Our result,s do not agree with his (vide infra) in this latter respect (wide $7) 2 t i WRIGHT AND MENKE ON MAXGANESE DIOXIDE. against which the thiosulphate was checked. In some cases the substance was boiled with acid ferrous sulphate in excess and the excess determined by ;t standard potassiam diuhromate solution, against which the ferrous sulphate was checked.Numerous experi-ments showed perfect identity between the average results of the two processes when perfectly pure dichromate and eiLrefully standardised solutions are employed (the iodine being standardised with specially prepared pure arsenic trioxide) ; only a trace of iodine was generally liberated on distilling the hydrochloric acid used into potassium iodide in a blank experiment; this amount was always subtracted (with some samples of acid and iodide this correction is very appre-ciable). The water expelled oa ignition was determined in two ways firstly by heating in a current of dry air and collecting the ex-pelled water in a CxC1 ttuhe; secondly by igniting weighed amounts and determining the loss of weight and the available oxygen in the residue.Subtracting this latter from the original available oxygen the oxygen expelled was ktiown ; and subtracting this from the loss on igniting, the water expelled was known. The average results by the two pro-cesses coincided perfectly. It was found that practically the whole of the water present was expelled on ignition the residue left on igniting several grams in a current of dry air in a large platinum boat never giving more than a very few milligrams of additional moisture on withdrawing the boat whilst still hot adding to its contents several times their weight of recently fusSd not completely cooled potassium dichrornate and heating again to fusion of the whole mass. Minute quantities of water were however thus obtained,* apparently indi-cating that on ignition a portion of the potash present became con-verted into KOH.This was corroborated by the circumstance that on treating with water the ignited substance (not fused with potassium dichromate) sensible quantities of potash were dissolved out forming a highly alkaline solution ; more than half of the potmsium present, however was usually still retained in a form of combination incapable of being dissolved out by boiling water. After 1 Mmth. Mean. Available oxygen. . 15.78 15.89 15.84 Water - - 5.60 Manganese monoxide and potash . . - - 78.67 100.11 * Morawski and Sting1 state (Zoc. cit. supra) that the same amount of water is expelled from a hydrated manganese dioxide containing potash by simple ignition as by fusion with potassium dichromate.Our experiments shorn that this result is only approximately true ; the residue left on ignition in a current of dry air unti %*RIGHT Ah'D MENKE ON MAKCASESE DIOXIDE. 27 After 3 Months. Mean. Available oxygen 15.80 15.86 15.96 16.03 - 15-91 Water . . . . . . . . . . . . 5.31 5.14 5.01 4.93 4.88 5.05 Manganese monoxide and potash 79-24 79.04 78.85 78.72 - 78-96; -99.92 After 5 Months. Available oxygen 15.93 16.02 16.05 16.16 16.04 Manganese monoxide and Water (by difference) 4.52 100.00 potash 79.54 79.34 - - 79.44 From these numbers it is evident that a very slight loss of water but no loss of oxygen attended the prolonged drying over sulphuric acid ; the experiments with other samples of hydrated manganese dioxide described below confirm these results indicating that no loss of oxygen whatever takes place either during the first drying of a moist precipi-tate over sulphuric acid or subsequently but that a continual pro-gressive loss of water takes place on long standing over sulphuric acid ; when a certain amount of water is thus lost (varying with the mode of preparation) the rate of loss becomes very small barely appreciable amounts being lost in several weeks.The amounts of manganese monoxide and potash severally present i n the sample dried f o r three months were carefully determined in several ways viz. heating with hydrochloric acid (or pure sulphuric acid) evaporation to expel the greatsr part of the excess of acid treat-ing with pure yellow ammonium sulphide (specially prepared and free from alkalis) and convert'ing the manganese sulphide into MnS04, by dissolving in pure hydrochloric acid evaporating to dryness with pure sulphuric acid and gently igniting a t a dull red heat ; the filtrate was evaporated to dryness in a platinum vessel and the residue ignited with sulphuric acid and the potash weighed as K,SO,.In some cases the weight thus obtained was checked by conversion into potas-siuni platinochloride; it was found that if a glass or porcelain evaporating vessel were used the potassium sulphate obtained was contaminated with lime silica alumina and alkalis derived from the ressel ; the same vessels hardly parted with a trace of corroded matter 110 further traces of moisture were yielded to a CaCla tube invariably yielded a little inoisture on adding to the still hot substance fused not quite cooled potassium di-chromate and heating again to fusion of the mass i.e.of the potassium dichromate. The amount of adhtional moisture thus obtained never exceeded 0.3 per cent. how-erer and averaged only about 0.2 per cent. with the substances examined 28 WRIGHT AND MEXE ON MANGANESE DIOXIDE. on evaporating down in them even strong hydrochloric acid solution. Another method tried was solution in hydrochloric acid evaporation to dryness heating finally to fusion in a crucible with a perforated lid tllrough which a stream of hydrochloric acid gas was passed in, weighing the residual mixed chlorides and then separating them by ammonium sulphide as before.It was found very difficult to avoid loss of manganese by volatilisation of the cliloride in t,his way ; direct experiments showed that MnClz can be readily sublimed id a current of hydrochioric acid gas on ignition for some short time and that the escaping gases when passed into water give an acid solution from which a perceptible residue of manganese chloride can be obtained on evaporation to dryness on the water-bath. A third method consisted of prolonged ignition in a boat in a current of hydrogen. At first potash sublimed in the fore part of the tube and for some hours the substance gradually lost weight even after the manganese was wholly reduced t o green oxide; but after some 12 or 14 hours it constant weight was attained and the residual MnO although usually just alkaline to moist test-paper contained only just discernible traces of potassium.* I n this way the following numbers were obtained :-MnO.K20. 7551 sulphates) { 75.51 as chlorides) 75.18 3-42 { ;:;; By sulphuric acid method (weighsd as By hydrochloric acid method (weighed By ignition in hrdrogen 75.37 -75-24 -75.20 -L_ Average 75-33 3.46 The sum of the MnO and K,O thus found is 78.79 whilst the amount of “manganese monoxide and potash” found as above described as being left on ignition (after subtracting the “ avai!able oxygen” also left) was 78.96 whence it would seem that 0.17 per cent. of water was retained by the ignited substance in the form of KOH. This quantity sensibly accords with the amounts of moisture obtained as above described on reheating the ignited substance with * It was found that the green manganese monoxide thus obtained when free from potash did not spontaneously oxidise in the air ; but if a minute quantity of potash were present the substance usually took up oxygen on standing in the air, becoming covered with a brown or black film the spontaneous absorption of oxygcn noticed by Wright and Luff (this Journal 1878 1 526) was doubtless due to the 13resence of small quantities of potash in the specimens observed to undergo this change which were at the time noticed to behave differently from pure maugauese nioiioxide prciared by long-continued ignition in hydrogen FRIGHT AND MESKE ON AlhKGhXESE DIOXIDE.29 a large excess of potassium dichromate; in three experiments the amounts of moisture thus olitnined were 0.19 0.17 and 0.30 p e ~ cent.; average 0.22 ; so that the total quantity of water present was 3-05. + 0.22 = 5.27 per cent. The percentages of MnO K,O 0 and H20 thus finally found correspond prett’y closely with those required for the formula-29Mn0.02,.K,0.8H,0. Calculated. Found. MnO 75.45 75.33 0 15.83 15.91 K,O 3.45 3.46 H,O 5.27 5.2 7 100~00 99.97 Prom this it is evident firstly that the water in this specimen of hydrated manganese dioxide corresponded neither with Rammels-berg’s formula 3MnO2.2H,O nor with Gnyard’s MnO2.N,0 but represented a much smaller amount of hydration which moreover, appeared to be not constant becoming slightly but sensibly rediiced on further long standing over sulphuric acid ; and secondly that the “ available oxygen ” present showed a deficiency as compared with that in Mn02 of about 2 parts in 29 or between 6 and 7 per cent.22.53 - 21-19 22-53 = 6-26 per cent. the available oxygen (more exactly present per 100 of MnO being x 100 in the sample examined, 7.533 16 71 and - x 100 in MnO, or respectively 21.12 and 22.53). Another specimen of manganene dioxide was prepared in the same way. Either from a difference of temperature during the precipita-tion or from some other unexplained cause however a consider-ably larger quantity of water was retained after drying over sulphuric acid for two months. By analysis as before the following average percentages were obtained indicating a composition pretty close to that of the preceding sample saving as regards the combined water agreeing fairly with the formula 34Mn0.032.K20.22H20 :-Calculated.Found (average). MnO 70.67 i0.68 0 14.99 14.91 2.80 KZO u (-3 H,O (expelled on ignition) . . 11*.59 11-56 100~00 99.95 9.C” - -30 WRIGHT AND MENKE ON MANGANESE DIOXIDE. The deficiency of oxygen in this specimen (as compared with that in MnO,) is almost identical with that in the previous one; for the oxygen per 100 of &In0 = - 70.68 = 6-39 per cent. is the deficiency in oxygen in this specimen 6.26 being that found in the formep one. The amount of water retained after two months is however more khan double that found in the former specimen. As in that case this amount was not constant for on further standing over sulphuric acid more water was lost; thns, after six weeks more (making fifteen weeks in all) the second speci-men contained only 9.54 per cent.of water. In order to see whether the deficiency in oxygen in these samples was possibly caused by spontaneous decomposition during drying a third specimen was prepared by adding to a hot nearly boiling solu-tion of permanganate twice its volume of concentrated nitric acid so that the total liquid contained upwards of 70 per cent. of HNO ; in a few minutes a large portion of the permanganate was decomposed but by no means all. The whole was then largely diluted with water the precipitate washed by decantation several times finally drained on a pump-filter and examined without drying in order to avoid the possi-bility of any loss of oxygen during the drying.An unknown quan-tity of the moist substance mas heated with hydrochloric acid and the evolved chlorine titratecl; the residual chlorides were evaporated down with sul'phuric acid to convert them into sulphates and the potash separated from the manqanese by ammonium sulphide as above described. In this way numbers were finally obtained for the weights of MnO K20 and 0 present yielding the following percentages relatively to their sum corresponding with the formula 43Mn0. ~,,,K,O. MnO 80.62 80.46 0 16.90 17.04 KzO 2-48 2.50 100~00 100~00 14'91 x 100 = 21.09 whence 22e.53 - 21.09 22.53 Caleulated. Found. -The deficiency in oxygen in this specimen was therefore almost identical with that found with the previous two specimens for the oxygen per 100 MnO was x 100 = 21.18 whence the defi-22.53 - 21'18 = 5.99 per cent.the ciency as compared with Mn02 was other two specimens giving respectively 6.26 and 6.39 per cent. deficiency. The amount of potassium retained in combination in this specimen however is perceptibly smaller thaii the quantity found in 17.04 80 4b 22.5 WRIGHT AND JIEXKE ON MASGANESE DIOXIDE. 31 Time in hours Oxygen lost (per 100 of original substance) . . Water lost at 210'. . Water expelled from re-sidue on ignition Total water --either of the other two samples doubtless owing to the effect of the larger proportion of nitric acid used. Some observations mere made on the loss of moisture and oxygen expel-ienced by the first two samples of snbstance on heating in n slow current of dry purified air for various periods to loo" and also to 210" (in a bath of naphthalene vapour).The loss of oxygen was determined by carefully titrating the substance before and after the exposure the Ioss of weight being also determined; by subtracting from the loss of weight the loss of oxygen found by the difference between the titrations (reckoned in each case per 100 parts of the sub-stance originally employed) the amoumt of water expelled TTW known. In some instances this amount was checked by igniting the dried sub-stance in a stream of dry air and collecting the expelled vater in a, CaC12 tube. The following numbers weFe obtained at 210" as the averages of several determinations in each instance :-3 0 -25 4 '33 0 -8'7 5 '20 Sample 11 I Sample I (dried 3 months omr sulphuric acid.) 8 0 '29 4 -03 -.- -47 0.03 9 15 - Nil (a gain of 0.02 was actually de-termined).0.23 I 0 25 *43 9 -9 -92 9.96 I I 1.77 30 0 -10 I ~~ __________~ ~ At 100" the following numbers were obtained as averages :-Sample 11. I Sample I. Time in hours Oxygeii lost (per 100 of original substanee) . -.--Water lo& a t 100". . Water expelled from re-sidue on ignit,ion . --Total water The total water capable of expulsion by heat deduced from the From these numbers it is evident that whilst the loss of oxyger previous analyses was 5.05 for Sample I and 11.56 for Sample 11 32 WRIGHT AND 31ENKE ON MAKGANESE DIOXIDE.experienced a t 100" is no greater than the experirnental errors of analysis at 210" a slight but perceptible evolution of oxygen appears to take place. The amounts of water retained at the ordinary tem-perature a t 100" and at 200° also appear to be very variable the substance retaining the most a t any one temperature also retaining the most a t any other temperature. Some specimens (such as those described in the 2nd Report) appear to become practically anhydrous at 200" in a few hours whilst the above specimens retained frcm 0.57 to 1.77 per cent. S. U. Pickering states (Zoc. cit. s y r a ) that from 3 to 6 per cent. of water was retained by the samples examined by him after drjing a t ZOO". 8 3. Mawganese Dioxide from Manganese Superchloride by precipitation with Water.I n order tlo see if potassium is carried down by manganese when precipitated from a solution of superchloride by copious addition of water a quantity of the substance above described prepared from potassium permanganate by the action of nitric acid (con-taining MnO = 70.68 K,O = 3-80 0 = 14.91 HEO = 11.56) was dissolved in about 50 parts of concentrated hydrochloric acici and the solution filtered through glass wool. To. one half of the so-lution a quantity of concentrated solution of potassium nitrate was added (the amount of salt added being about treble the weight of the dioxide used) and the whole then thrown into water; after skand-ing 24 hours the precipitate was washed by decantation and finally on the pump-filter. The other half was precipitated by addit,ion of water only.The substances obtained were examined whilst still wet by boilirg with hydrochloric acid to determine the oxygen and separating the manganese and potassium from the resulting chlorides as above describcd. The following percentages were obtained, calculated on the sums of the K20 MnO and 0 found corresponding respectively with the formula 49Mn0.04s.2K20 and 113&h0.01m.K20. Ma 0. 0. E20. Sample prepared with Found . . . . . . 78.38 17-32 4.29 potassium nitrate { Calculated . . 78-45 17.31 4-24! Sample prepared with- Found. . . . . . 81-.55 17-50 0.95 out {Calculated . . 81.49 17.55 0-96 As indicated by the experiments of Pickering each of these specimens contained less oxygen than corresponds t o 1\9nO2 the oxygen per 100 of MnO being respectively 22.11 and 21.46 corresponding to de-ficiencies in oxpgen of 1.86 and 4.75 per cent.respectively; thes WRIGHT AXD MENKE ON MANGANESE DIOXIDE. 33 numbers moreover are in harmony with the experiments subsequently described ($ 7) the deficiency in oxygen being least in the sample containing the most potash. The potassium present' per 100 of MnO is greater in the first samplc than in the original snbstance but less in the second example :-2-80 Original substance K,O per 100 MnO = 7m x 100 -= 2.96 Sample prepared with KNO ,, , without ,, 4.29 x 100 = 5.47 78.38 Oeg5 x 100 = 1.16 81.54 whence it results that decomposition of the added potassium nitrate (or of the potassium chloride formed from it by the action of the strong hydrochloric acid) must have been produced by the manganese dioxide a t the moment of its formation from the superchloride and the potassium carried down in combination with the manganese and oxygen.I n the second sample the effect of the large quantity of acid has diminished the amount of potassiiim retained by the manganese, just as was observed with nitric acid previously (9 2). It would thus seem that the distribution of the potassium in solution between the mineral acid and the precipitated manganese dioxide is regulated, amongst other things by the relative masses of acid and mariganese present (possibly also it depends on the state of dilution tem-perature &c.) , § 4. Manganese Dioxide pyepared by the Action of Xulphzcric Acid on Potassium Permaizgannte.A warm concentrated solution of potassium permanganate was treated with its own bulk of pure snlphuric acid cautiously dropped in and the boiling hot fluid largely diluted with water. The precipi-tate which subsided gave the following numbers after drying for some days over sulphuric acid until a,pparently perfectly dry approximately bearing out Guyard's statement that the hjdrnted manganese dioxide formed by precipitation contains MnO,.H,O ; a notable amount of potash was however also present the numbers agreeing with the formula 23MnOz.KZ0.22H2O :-Calculated. Found. MnO 65.57 65.51 0 14-77 14-89 K 2 0 . . 3.77 3.69 H2O 15.89 15.91 (by difference) 100'00 100~00 VOL. XXXVII. 34 WRIGHT AND JIENKE ON MASGANESE DIOXIDE. No deficiency of oxygen a t all was here perceptible the oxygen per 100 MnO found rather exceeding that due to MnO (through experi-14-89 niental errors doubtless); for - x 100 = 22.73 whilst MnO, 65.51 requires 22.53.On standing over sulphuric acid a t the ordinary temperature a loss of water was noticed without loss of oxygen ; after another fortnight the sample contained MnO = 67-74 0 = 15.25 K,O = 390 H,O = 13.11 corresponding with the formula 23MnOL.K20.17H,0 and in-dicating therefore a loss of nearly one-fourth of the water. The oxygen per 100 MnO was as before tho same as that due to Mn02, within the limits of experimental error; for ~ x 100 = 22.51 (MnO requires 22~~53). After yet another fortnight the percentage of water was 12.77 indieating that the rate of loss of water had become greatly reduced.From these numbers and those obtained with the specimens above described prepared from potassium perinanganate by means of nitric acid (9 2) it would seem that the hydrated manganese dioxide thrown down by precipitation a t first approximates to MnO,.H,O and that the water is gradually lost over sulphuric acid but not completely a cci*tain amount (depending probably on the physical state and ap-parently on the quantity of K,O present vide §§ G and 7 ) being retained with considerable firmness even a t temperatures up to 210'. 15.25 67.74 § 5. Manganese Dioxide prepared by the Action of Sulp7LzLr Dioxide on Potassium Perma? ganicte. A stream of washed sulphur dioxide was led into a cold solution of potassium permanganate which was kept in large cxoess throughout: the brown precipitate was washed thoroughly by decantation and on tile pump-filter and then yielded the following numbers (analysed as above described whilst still wet) agreeing with the formula-1 4~MnO.O,,.K2O :-Calculated.Found. MnO 77.66 77.74 0 . . . . . . . . . . 15.00 14.9 7 KzO 5.34 7.29 100~00 €00-00 A very large deficiency in oxygen is here noticeable the oxygen per 100 of B h O being 2 x 100 = 19.26 whence the deficiency rela- 14-97 77.7 IT RIGHT AND MESKE ON MANGANESE DIOXIDE. 35 9 6. Manganese DioaXe preyared by the Action of Alcohol or Glyceriw on Yotuss L'um Permanganate. According to Morawski and Sting1 (loc. cit. supra) the brown pre-cipitate formed when glycerin or alcohol is added to permanganate solution and the whole gently warmed contains the elements of the compound 8MnO2.K20.3H20 after drying at 100".Our experiments do not confirm this. A nearly saturated cold solution of permanga-nate was added to glycerin dissolved in 6 or 8 parts of water and the whole gently warmed (temperature ultimately about SO-35'7. After a few minutes the whole of the permanganate was reduced the brownish-black muddy precipitate was thoroughly washed and ana-lysed as above described whilst still wet ; two different samples A and B gave the following numbers the numbers in the column headed C being obtained with a third specimen in the preparation of which alcohol was substituted for glycerin :-A. B. C* Available oxygen 12.99 11.41 14.37 MnO '78.56 82-36 70.78 K,O 8.45 6.23 14.85 100~00 100.00 100~00 These numbers correspond respectively with the approximate formula? 12MnO.O,.KZO ; 35Mn0.02,.2K20 ; and 20Mr~O.0~~.3K2.0, differing widely from one another and from Morawski and Stingl's formula (which becomes 8M11O2.KzO when reckoned on the anhydrous substance) not only in the presence of different quantities of potassium relatively to the manganese but also in the manganese being asso-ciated with very much smaller quantities of oxygen than correspond to MnO,. After drying over sulphuric acid and finally at 100" for six hours these three substances contained respectively 9.77 10.21 and 9.57 per cent. of water expelled on ignition (collecbed in a CaC12 tube), thus indicating the retention at 100" of much larger quantities of water than were observed with the substances prepared by heating permanganate solution with nitric acid (9 2).Morawski and Stingl's formula requires 6-44 per cent. of water. According to Morawski and Stingl,. the same compound, 8Mn0,.K,0.3H20 is produced when hydrated manganese dioxide is heated with potassium hydrate or carbonate solution well washed and dried a t 100". We treated with a large excess of dilute caustic potash solution the subst ince described in the next section prepared by actkg with hot dilute manganese suiphate solution on excess of hot potas-sium permangaziate solution the whole being kept in boiling water €or D 36 WRIGHT AND 'MENKE ON MANGANESE DIOXIDE. 12 hours after thorough washing and drying over sulphuric acid for a few days till apparently quite dry the following numbers were ob-tained agreeing with the formula 21 Mn02.4K20.19H20 (approxi-mating to Gorgeu's formuh SMn02X20), Calculated.Found. MnO 58.59 58.51 0 13.20 13.24 K20 14.77 14.87 H20 13.44 13-33 (by differeuce). 100.00 100-09 After drying a t 100" for several hours this substance retained 9.73 per cent. of water capable of expulsion on ignition ; whence it would seem a s indicated also by the numbers obtained with the substances prepared by acting on permangannte wit5 alcohol and glycerin that the presence of much potash diminishes the ease with which water is expelled ; experiments corroborative of this are also described in the next section. S 7. LWanganese Dioxide prepared by the Action of Potassium Perrnnnga-nnate on Manganese Xulphate.In order to test the correctness of Giirgeu's and Guyard's statements (supra) as to the amount of oxygen relatively to the manganese preci-pitated under different conditions four experiments were made with the same solutions of pure manganese sulphate and potassium perman-ganate each solution containing about 5 per cent. of the dissolved salt. In the first and second experiments the manganese sulphate solution was slowly poured into a considerable excess of permanganate the solu-tions being both a t 130-85" in the first case and cooled down (after dissolving the salts with the aid of heat) to the ordinary temperature in the second case. The third and fourth experiments were analogous respectively to t h e first and second as regards temperature but dif-fered in that the permanganate solution was poured into a considerable excess of manganese sulphate.The precipitates were well washed by decantation and finally on the pump-filter and examined whilst still wet an unknown weight being boiled with hydrochloric acid to deter-mine the oxygen and the manganese and potassium determined in the resulting mixed chloride solution. The following percentages were deduced from the sums of the weights of MnO 0 and K,O thus found corresponding respectively with the approximate formulae :-No. I . . 15Mn02.K?0. , 2 . . . . . . '72A1n0.0,,.3K20. , 3 . . G5Mn0.062.2K,0. , 4 . . . . 66Mn0.06,.K,0 KRIGHT AXD MENKIE OX NBNGASESE DIOXIDE. 37 3 h O . 0. &!O. {Found 76-32 17.M 6-62 Calculated 76.12 17-16 6.72 i8-24 li.39 4.37 , 2{F:und Calculated 78.28 17.40 4.32 Fourid 79-62 17-14 3-24 Calculated 79-64 lie12 3.24 81.21 17.17 1.62 , 4 {Found Calculated 81.19 17.18 1-63 I n the case of sample No.1 the deficiency in oxygen is so small as to be almost within the limits of experimental error; the other samples especially the two last show perceptibly larger amounts of deficiency :-Oxygen per 100 Deficiency compared with of Mn.0. Mn&. 17.06 0-1 8 0.3 I 22.22 - - 1'7.39 78.24 1 *(30 rn 22.53 -1-38 81-19 t L 35 No. 1 i6.32 x 100 = 22.35 'md = 0.81 per cent. . . . . x 100 = 22.53 - 1-38 9, 17.14 x 100 = 21.53 ~ - 4.44 ,, , 2 ) 3 ) ) 4 l7*I7 x 100 = 21.15 - = G.17 ,, It would thus seem that whilst the formation of such substances as the Mn5011 and other oxides yet more deficient in oxygen described by Guyard and Gorgeu did not take place in these experiments yet the statement of Guyard that precipitation in the cold yields a substance more deficient in oxygen than one similarly prepared a t about 80" is perfectly correct specimens Nos.'L and 4 (prepared cold) containing re~pect~ively less oxjgen relatively to the MnO present than Nos. 1 and 3 (prepared a t 8 0 - 4 3 " ) . It is also noteworthy that the amount of combined potassium in these four specimens varies inversely with the deficiency in oxygen in other words the more potassium oxide is pre-sent combined with MnO, the less MnO is carried down similarly combined. As might be anticipated too more MnO is thus carried down when the MnS04 is in excess than when the permanga-nate is.By using more dilute solutions of manganese sulphate and pelaman-gauate keeping the latter in excess and precipitating hot (at about 80-90-)) it is possible to obtain a precipitate containing every trace of the manganese present as MnO (associated with potash). Thus experiment No. 1 was repeated employing solutions of one-tenth the strength (0 5 per cent. of each salt present). The precipitate obtaine 38 WRIGHT AND MENKE ON MANGANESE DIOXIDE. after drying over sulphuric acid for a few clays till apparently quite dry gave numbers agreeing with the formula 1 1MnO?.Kz0.7H20, and exhibited no deficiency in oxygen :-Calculated. Found (average). MnO 66.35 65-85 0 14-95 14.94 K,O 8.00 8.26 HzO 10.70 10.95 (by difference).100~00 100-00 Oxygen per lOC MnO = 14'94 - x 100 = 22.69 MnO requiring 65.85 22-53. It is noteworthy that in this case the amount of potash present relatively to the manganese is greater than was the case with speci-men No. 1 which exhibited a small deficiency in oxygen ; the water present in this specimen was considerably below that required for the formula MnOz.HZO but was close t o that required for 3&In0.2Hz0 : 2 H O - 36 3Mn0 213 t,he latter gives the ratio - - - = 16.90 per cent. whilst 10-95 - there was found - - 16-63 per cent. So far as this particular 65.89 specimen is concerned therefore the view of Rammelsberg that hydrated manganese dioxide is 3Mn02.2H20 would appear to be con-firmed ; but the previously described experiments indicate that the composition is actually variable between the limits Mn02.H20 and something roughly approaching the anhydrous state according to the length of time that the specimen is allowed to stay over sulphuric acid which is further confirmed by the following numbers represent-ing the percentages of water expelled on ignition and collected in a CaClz tube from the specimens Nos.1 2 3 and 4 just described each dried over sulphuric acid for oue week and three weeks Nos. 1 and 2 mere coppery cdoured when first examined Nos. 3 and 4 nearly black. Percentage of Water collectecl. Dried over H,SOA 1 week. Dried 3 weeks. No. 1 13.39 13.22 . 3 . . . . . . . . 8-28 7.50 4 9.41 9.08 , 2 16-53 12-90 As previously indicated 9 6 t'he specimens containing most potash parted with water least rapidly WRIGHT AXD JIENKE ON NANGANESE DIOXIDE 39 It is possible to obtain complete precipitation of manganese as MnOz in the cold by adding zinc sulphate t o the permangannte solu-tion and then gradually pouring in the manganese salt SO that the permanganate is always in excess.Determinations made thus with known quantities of manganese furnished amounts of precipitate con-taining available oxygen equal to 37.5 to 37.65 per 100 MnO in the mangar.ese salt used. Since the precipitate is formed in virtue of the reaction-3MnX + 2KMn04 + 2H20 = 5MnOZ + KzX + 2H2X, three-fifths of the manganese in the precipitate comes from the man-ganese salt and two-fifths from the permanganate wherefore the available oxygen due to the manganese was equal to.0.6 x 37.5 to 0.6 x 37-65 or 22.50 to 22.59 per 100 MnO MnO requiring 22.53 (vide 9 9). Since these experiments were made a paper by Volhard has ap-peared (Annulen 198 318) in which the author states that pm manganese dioxide containing a t most traces of potash is obtainable by dissolving 10 grams of manganese sulphate in half a litre of water, adding 100 C.C. of nitric acid sp. gr. 1.2 heating on the water-bath, adding excess of permanganate keeping on the water-bath for an hour and washing the precipitate at first with water acidulated with nitric acid and by decantation and finally on the filter and drying on bibulous paper &c, The foregoing experiments however mould indicate that a greater amount of potassium is carried down in combination with the mangz-nese dioxide than would appear from Volhard’s statements.On pre-paring some of the prcjduct in exact accordance with his directiom, thoroughly washing and drying for a few days over sulphuric acid till apparently quite dry to the touch the following numbers were ob-tained indicated by the formula 30Mn02.K,0.1 7H20 :-Calculated. Found (average). MnO 70.76 $0.65 0 15.95 i 6 m K20 3.12 307 H20 10-17 10.28 100*00 100-00 -Ratio of MnO to available oxygen 100 to 22-62. Calculated for MnO 100 to 22.53. The amount of potash in this sample relatively t o the manganesc was however notably less than was the case with either the last-described substance (prepared from 0.5 per cent.solutions of mangn 40 WRIGHT AND MEXKE OX IIAR’GAJSESE DIOXIDE. nese sulphate and potassium permanganate) or the previously described substance No. 1 (prepared from 5 per cent. solutions), doubtless owing to the influence of the added nitric acid; so that Volhard’s observation that the amount of potsash carried down is lessened by adding nitric acid is (as also indicated by the previously described experiments §$ 2 and 3) perfectly correct the only error being in the actual amount of potash carried down which is evidently much more than mere traces. 9 8. Nanganese Superoxide prepured by the Action of Air a n d Cuustic Potash on Manganese Chloride. Manganese chloride (prepared by boiling permanganate of potas-sium with h”ydroch1oric acid and evaporation nearly to dryness to expel the excess of acid) was dissolved in some 20 parts of water and excess of caustic potash added the whole was placed in a flask with a wash-bottle cork and tube attached so that by attaching an aspi-rator t o the shorter tube a continuous current of air could be sucked through the whole and the manganese oxidised in accordance with Weldon’s well known method.After some 30 hours’ treatment a large portion of the manganese was peroxidised ; the brown precipi-tate after thorough washing contained (reckoned as anhydrous) :-Available oxygen 10.24 Manganese oxide MnO 87.53 K20 2 2 5 100~00 A little lime derived from impurity in the caustic potash was also present. These numbers are represented by the formula 58BiIn0.0,,.K20.The great deficiency in oxygen is doubtless due to the action of the air not having been prolonged sufficiently and being allowed t o take place at the ordinary temperature. A considerable quantity of potash was permanently combined with the manganese notwithstanding. 8 9. Manganese Dioxide precipitated by Byomiize iiz presence of Potassium Acetake. It has long been known that manganese dioxide precipitated from an acetate solution by bromine or chlorine is apt to carry down alkalis with it increasing its weight so much so that in various analytical text-books (e.g. Fresenius’s) it is stated that the precipitate must be dissolved in acid and reprecipitated as carbonate before ignition t o convert it into Mn,04. In order to see how much potassium could be carried down in presence of a very large amount of potassium salts TRIGHT AND MESI(E O S 31A4?\'GBN;ESE DIOXIDE.41 some potassium permanganate was boiled with hydrochloric acid and the solution treated with a quantity of potassium acetate in quantity representing some 15-20 times as much potassium as there was pre-sent manganese (to avoid presence of lime the potassium acetate was made from redistilled acetic acid and calcined cream of tartar precipi-tated from pure nitre by tartaric acid). The whole was heated on the water-bath and a considerable excess of bromine dissolved in strong potassium bromide solution added so that altogether the potassium present was probably about 25 times the weight of manganese in solu-tion. After standing on the water-bath for about' an hour the pre-cipitate was washed by decantation and on the pump-filter and annlysed wet as above described with the following results in per-centages of the sum of the K20 MnO and 0 found corresponding nearly with the formula 501\hO2.7KZO.Calculated. Found. MnO 70.89 71.03 0 15.97 1594 K,O 13-14 13.03 100*00 200-00 15.94 Oxygen per 100 MnO = 7,,,03 ~ x 100 = 22.44. Calculated for MnO = 22.53. After standing over sulphuric acid for a week this substance con-tained 14.18 per cent. of water corresponding with 50Mn02.7K,0.4GH20. After three weeks the quantity was diminished to 8.90 per cent. num-bers being obtained agreeing with the formula 50Mn02.7K,0.27H20. Calculated. Found. MnO 64-61 64.73 0 14.56 14.50 K,O 11.99 11.87 H,O 8.84 8.90 100*00 1@0*00 14.50 Oxygen per 100MnO = ___ 64.73 x 100 = 22.40.NnO2 requires = 22-53. It is hence manifest that the sample lost water on drying over sul-phuric acid to considerably below the amount due to t,he formula 3Mn02.2K,0 like most of the other samples examined ; further tha 42 WRIGHT AND MENKE ON ;MANGANESE DIOXIDE. loss of oxygen accompanied the desiccation ; and thirdly that the de-ficiency in oxygen compared with MnO was but; small viz. a t most = 0.58 per cent. 22-53 Other samples prepared in a similar way but in presence of much smrlller quantities of potassium salts exhibited much larger de-ficiencies in available oxygen the deficiency being apparently increased if the precipitation took place a t temperatures considerably below 90-100".The largest deiiciencynoticed was in a specimen which gave (after standing over scllphuric acid for a few days till dry to the touch) numbers agreeing with the formula 64Mn0.O,,.K20.63H20, exhibiting a deficiency of upwards of 14 per cent. conjoined with but a small percentage of potash. § 10 Volumetric Deternzim$ion of Xangmese. It has been shown by Kessler (Zeits. Anal. Chem. 1879 18 Part I) that by slowly adding manganese solution to hot bromine-water con-taining zinc cbloride and sodium acetate and finally boiling the whole of the manganese can be thrown down a s MnO (associated with zinc) wliilst Pat'tinson has simultaneously found (this Journal 1879, 1 365) that ferric chloride or zinc chloride will produce the same result when added to the manganese solution along with bromine-water calcium carbonate being finally added to the hoti liquid.We have repeated the experiments of these observers both in their original forms and with modibaltions and can corroborate their accuracy, with certain reservations in the latter case. Substances contsiriing known a,mounts of manganese were dissolved to known volumes and eqnal aliquot parts taken and examined in vaiious ways-(a) by exactly following Kessler's directions ; (6) using Pattinson's originnl method ernployiiig bromine-water and ferric chloride ; (c) employing Pattinson's modified method (Zoc. cit. 371) employing zinc sulphate in lieu of ferric chloride ; ( d ) using a simple modificatioiz of this last process viz. adding to the somewhat acid hob solution a considerable excess of bromine-water and then freshly precipitated zinc carbonate.In all four cases results were obtained (by washing and titrating the precipitates with €errous sulphate and dichromate or permanganate) agreeing closely with each other and with the amount of manganese actually present the differences between the results of the four pro-cesses not being greater than the differences between the results of repetitions by the same process. To obtiin the best results we found it desirable to boil the liquid and precipitate after digesting on the water-bath for a few minutes (the precipitat'ion being effected at a temperature as near 100" as possible) so as to expel all free bromine WRIGHT AND JIEX'KE ON MANGANESE DIOXIDE 43 as directed by Kessler.The precipitates obtained thus by methods a G and d contained the whole of the manganese present as Mn02 (of course associated with zinc oxide &c.). When the ferric chloride method was used however the filtrate almost invariably contained permanganate in solution whereas this never occurred with any of the processes in which zinc was employed. We found that the best method of estimating the manganese thus contained was the comparison of its tint with an equal bulk of water coloured with measured quantities of deuinormal permanganate solution ; this compa ison is not readily made unless the whole o r almost the whole of the free bromine has been boiled off owing to the alteration in colour produced by the bromine. Reduction by nlcohol &c.invariably gave a precipitate containing less available oxygen than corresponded to tbc manganese contained therein (vide $ 6) and hence led to an under estimation of the total manganese present. We obtained good results when the solutions were so diluted that about 150 to 200 C.C. of total fluid (in-cluding bromine-water) were present for every 0.1 gram of MnOz precipitated using a quantity of zinc sulphate or ferric chloride con-taining from 1.5 to 2 parts of metal for 1 part of Mn02 and sufficient bromine-water to make the supernatant fluid after precipitation moderately dark amber or sherry colour in short an excess of two or three times the amount of bromine actually requisite for oxidation of the manganese. All these processes however are open to the objection that they require the use of bromine (or bleaching powder) and are apt to im-pregnate the air of the laboratory disagreeably with the vapoars thereof unless worked in a fume chamber the following modification of Guy ard's permanganate process we found to give good results and to be less troublesome as regards manipulation than any of the others.The solution which should not contain much free acid especially if hydrochloric acid is present is diluted with water until it contains no more than equivalent to 0.1 gram MnO in 150 or 200 C.C. ; zinc sul-phate to the extent of some 10 parts of crystallised salt per 1 of MnO, to be precipitated is then added to weak (about 0.5 per cent.) solution of permanganate the quantity of which is somewhat more than that required to precipitate the manganese salt ; this latter is then slowly poured into the permanganate (not vice uersd) without heating and with shaking or stirring.In a few minutes most of the supernatant pink fluid can be poured off through a glass-wool filter on to which the precipitate is brought and washed finally the precipitate is titrated with ferrous sulphate and dichromde or permanganate ; three-fifths of the manganese dioxide thus found is due to the manga-nese in the solution examined. To minimise sources of error the dichromate or permanganate solution should be standardised in th 44 WRIGHT AND RIESRli ON I\IhNGANESE DIOXIDE. same way with a manganese solution of known strength ; if the per-manganate solution be hot too high results are apt to be obtained through partial decomposition of the excess of permanganabe either by heating alone or more probably by the action of traces of volatile organic matter in the water used for washing dust &c.; whilst if the zinc sulphate be omitted and the precipitation effected in the cold, too low results are obtained owing to the formation of a precipi-tate containing a deficiency of oxygen (§ 7). The following numbers obtained with equal bulks (50 c.c.) of one and the same manganese solution illustrate the nature of the results obtainable similar values being obtained in numerous other analogous experiments ; the numbers are given in cubic centimeters of quintinormal ferrous solu-tion (+ x 28 gram Fe in the ferrous state per litre) oxidised by the manganese dioxide precipitabed.1. Precipitated by adding to boiting solution of permanganate 32.8 C.C. 2. Precipitated by adding to coZd solution of permanganate without ZnS04 32.25 ,, 3. Precipitated by adding to coZd solution of perrnanganate with ZnS04 3‘2.65 ,, 4. Precipitated hot by Pattinson’s original pro-cess (ferric chloride and calcium car-bonate) after correction for a small quan-tity of permanganate formed. . 32.55 ,, 5. Precipitated hot by Pattinson’s modified process (zinc sulphate and calcium car-bonate) 32.6 ,, 6. Precipitated hot by adding bromine-water and zinc carbonate 32.S5 ,, 7. Precipitated hot b3 adding bromine- water and 20 parts sodium acetate to 1 of MiiO, formed 32.1 ,, 8. Precipitated by exactly following Kessler’s directions (bromine-water sodium acetate, and zinc chloride used).. 32.6 ,, Evidently the boiling permanganate method (1) gives slightly too high a value through decomposition of the excess of permanganate, whilst the cold permanganate without ZnS04 (a) and the sodium acetate without ZnSOa (7) methods precipitate substances deficient ir, oxygen as shown above ($8 7 and 9). The other methods give practi-cally identical results ; of t>hese No. 3 involves the least trouble and inconvenience WRIGHT AXD MENKE OX JSAKGASESE DIOXIDE. 45 tj 11. Manganese Dioxide prepared f r o m Hanganese Nitrate by Heat. Pure manganese carbonate was dissolved in just sufficient dilute nitric acid and the solution evaporated to a syrup which was then heated to 160-165" in an air-bath for some hours.Precisely as described by Gorgeu a pyrolusite-like substance was thus obtained after treatment of the product with boiling water and thorough wash-ing when dried in the air or over sulphuric acid for a few days a little moisture was retained a portion only of which was expelled on heating to 210" for several hours. The following numbers were ob-tained the manganese being determined ( a ) by weighing as MnSOJ, ( b ) by igniting and determining the " available oxygen" left in the residue and (c) by reduction in hydrogen at a red heat. (a) (6) (c) Mean. MnO . . 80.74 80.45 80.63 - 80.61 0 (by iodine process). . . . 18.19 18-23 18.39 - 18.23 H,O by ignition and col-lection in a CaC1 tube. . 1.32 1.25 1-02 0.96 1.14 The oxygen On heating 5t vapour-bath) in of 0.34 per cent.-99-98 x 100 = 22.61. 18.23 par 100 of MnO found is 8~,.6~ MnO requires 22.53. portion of this Substance to 210" (in a naphthalene a current of dry air for f'our hours a loss of weight only was observed which did not increase even after nine hours. The residue thus left when ignited gave off visible quan-tities of water the amount collected in a CaCI tube being 0.62 per cent. No loss of oxygen whatever occurred even in nine hours not oily was the loss of weighl a trifle uiader that due to the average water found (0.34 + 0.62 = 0.96 against 1-14 per cent.) instead of being above it a s would be the case were oxygen expelled as well as water, but further the residue left gave on titration 18.25 of oxygen per 100 of original substance or precisely the same amount as that found before drying.According to Gorgeu pure manganese dioxide is produced even if other metallic nitrates (e.g. potassium calcism &c. nitrates) are present in the manganese nitrate employed. I n order to see whether this substance is wholly free from potassium, a mixture of about equal weights of manganese nitrate and potassium nitrate was dissolved in water evaporated to a thick syrup on the water-bath and heated to 160" for several hours. The pyrolusite-lik 46 WRIGHT AND MENKE OX NAXGASESE DIOSIDE. substance obtained was crushed and well washed with hot water and then contained (after drying in the air)-MnO. KZO. 0. H20 (by difference). 79.57 1-64 17-67 1.32 = 100 Oxygen per 100 MnO - 22-27 The potash present however was apparently due to the difficulty of thoroughly washing out all soluble potassium compounds for another specimen similarly prepared but ground up fine in a mortar gave, after well washing and drying in the air the following numbers :-MnO.K,O. 0. H20 (by diaerence). 79-88 0.37 17.97 1.78 = 100 Oxygen per 100 MnO = 22.50 Whilst on grinding up in an qgate mortar and boiling with water for sonic time perceptible amounts of potash salts were dissolved out and the residue left contained only traces of potash. Hence Giirgeu’s statements as t o the non-formation of a manganese dioxide contain-ing potash by heating the nitrate of manganese in presence OE potassium nitrate are evidently quite correct notwithstanding their 4 priori im-probability in view of the decomposition of potassium nitrate and other salts by hydrated manganese dioxide; and as stated by him the substance obtained exhibits but little if any deficiency in oxygen.A notable distinction between this substance and the other bodies examined also was the following on shaking up with concentrated coZd sulphuric acid and allowirg to stand for twenty-four hours the substance subsided leaving a colouriess supernatant fluid (manganic sulphat,e was however formed if the liquid were strongly heated). Every other specimen described in this paper gave a pink violet-pink, or violet supernatant fluid (manganic sulphate presumably) on treat-ment with cold acid and clearing by subsidence. 0 12. ConclusWns. From the preceding experiments which are partially repetitions of those of Pickering Kessler Pattinson Gorgeu Guyard and others, the following conclusions may be drawn :-(1.) 1S;Ianganese dioxide prepared by precipitation processes and freed from extraneous water is (leaving out of sight metallic oxides carried down with it) a hydrate &InO2.H,O ; but it is impossible to keep this hydrate in dry air as it loses water readily at the ordinary temperature.The rate a t which the water is lost appears to be very variable being the more rapid cceteris paribus the less combined potash is present; no definite hydrate of any kind sfable in dry air appears to exist ‘as every specimen examined continually lost water over sulphuric acid VRIGHT AND MENKE ON MANGANESE DIOXIDE.47 even after several months when the amount of water present was ieduced to about 5 per cent. ; although one or two specimens mere obtained which lost water only slowly when they attained a composit:on approximating to 3MnOp.2H20 the great majority lost much more water before the rate of further loss became small. (2.) Neither at the ordinary temperature a t IOO" nor a t 210" does the hydrated substance become anhydrous even after the lapee of many months in the first case and hours in the two subsequent cases ; the amount of water thus quasi-permanently retained is very variable. (3.) Neither at the ordinary temperature nor at loo" is the expul-sion of water accompanied by any material loss of oxygen if indeed any a t all is lost at 210" however a slow regular loss of oxygen takes place on continued heating (the substance prepared by heating the nitrate does not lose oxygen thus).(4.) Hydrated manganese dioxide if prepared in presence of potas-sium salts invariably carries down with it in combination more or less potash the amount thus fixed varies with the circumstances; in presence of much free acid (nitric hydrochloric) the amount is les-sened whilst on boiling with caustic potash or digesting a t loo" it appears to become a maximum corresponding nearly with the ratio described by Gorgeu viz 5Mn02.Ki0. In presence of certain potassium salts e.g. acetate nitrate &c. the precipitate appears to decompose a portion of the salt setting free the associated acid to a greater or a less extent. (5.) When tbe precipitation takes place under such conditions that not much potash (or other equivalent metallic oxide) can be carried down by the manganese dioxide a greater or lees deficiency in oxygen (compared with Mn02) is noticeable in the precipitate ; i.e.manganese itself is carried down a s MnO in the precipitate. This is especially noticeable when the substance is formed by adding potassium permanga-iiate to excess of manganese sulphate or when the precipitate is produced by the action of a large quantity of nitric acid on potassium permanganate or by diluting with water a very acid solution of man-ganese superchloride (Piekering). Heating the solution appears to diminish the deficiency of oxygen in the precipitate (Guyard). (6.) By operating in particular ways the deficiency of oxygen in this precipitate may be reduced to very small limits or nil; for example adding manganese sulphate t o excess of potassium perman-ganate solution the liquids being not too concentrated and a t a tern-perature near 100" (Guyard) ; adding bromine to a hot solution of a manganese salt in presence of potassium acetate and other potassiirm salts jointly containing a very large quantity of potassium relatively to the manganese present or iu presence of an acetate and a zinc sal 43 WRIGHT ASD MEXKE ON MANGANESE DIOXIDE.(Kessler) or of ferric chloride and calcium carbonate (Pattinson) or of zinc carbonate. (7.) Acting on potassium permanganate solution with reducing agents such as sulphur dioxide alcohol or glycerin gives rise to a precipitate containing much less available oxygen than corresponds to the manganese present ; potash is carried down in combinatioii with the precipitate but the composition of the latter is very variable.In no case has any substance been obtained of the composition (after drying at 100') Mn4KH,01 (or 81\iIn0,K20.3H,0) said by Morawski and Stingl to be always produced under such circumstances ; nor is this substance formed by heating precipitated manganese dioxide (containing a little potash) with caustic potash solution for some hours, as stated by them; the product thus obtained approximated to the composition ascribed years ago by Gorgeu viz. 5M302.Kz0 (reckoned on the anhydrous substance). (8.) The statements of Gorgeu as to the formation of sensibly pure MnO by heating manganese nitrate to 160° and the freedom of the pyrolusite-like product from combined potassium even though potas-sium nitrate is present in large quantity are perfectly correct.(9.) The statements of Volhard as to the formation of pure hydrated manganese dioxide by precipitating manganese sulphate with excess of permangarlate in presence of nitric acid in the way described by him, are only partially correct inasmuch as the product contains several per cents. of combined potash instead of traces only at most as stated by him ; but the manganese and available oxygen in the product are sensibly in the ratio required for Mn02. (10.) The statements of Morawski and Stingl. as to the complete expulsion of combined water in hydrated manganese dioxide containing potash by direct ignition are only partially correct ; almost the whole is thus expelled but a little is retained apparently through the formation of KOH which can be dissolved out of the ignited product by water.(11.) Long continued ignition in hydrogen removes all or nearly all, of t,he potash present in a hydrated manganese dioxide containing potash leaving behind sensibly pure MnO of a much brighter green colour than that formed by the similar reduction of manganese dioxide free from potash. (12.) Manganese monoxide retaining a little potash (prepared by reducing dioxide containing potash in hydrogen but not completely expelling all the potash present) frequently oxidises spontaneously in tbe ordinary moist air whereas when free from potash the monoxide does not appear so t o oxidise. (13.) Manganese chloride is sensibly volatile in a stream of HC1 gas at a red heat FRED. D. 1 3 ~ 0 ~ 1 7 ~ OX FRACTIOSAL DISTILLATION. 4 9 (14.) Several different processes for estimating manganese volu-metrically have been compared and the work of Pattinson and Kessler confirmed ; sundry new modifications OF conihinztions of previouslj-known processes have been examined and found to give satisfactory results the one suggested as most convenient and exact being precipi-tation by addition i ~ the coZd of the manganese solution to be deter-mined to excess of permanganate solution containing zinc sulphate, collection on a glass wool filter and titration with acid ferrous sulphate and permanganate or dichromate solution preferabl~ stnndardised in the same way with a manganese solntion of known strength