,dissertation presented for the degree of ,doctor of ,philosophy to the ,board of ,university ,studies of the ,johns ,hopkins ,university by ,arthur ,john ,hopkins4 #ahic4 ,acknowledgment---- ,the work recorded in this paper is the result of a suggestion given by ,professor ,h4 ,n4 ,morse4 ,it has received his careful attention throughout its course4 ,for his instruction and exact criticism1 ,i wish to offer my acknowledgment and thanks4 ,i wish also to express to ,professor ,ira ,remson my appreciation of his interest and instruction and to offer to ,dr4 ,j4 ,s4 ,ames my thanks for his instruction in ,physics---- ,table of ,contents4 ,page4 ,i ,introduction #a ,,ii ,description of ,apparatus #c ,,iii ,action of ,manganese ,dioxide on ,potassium ,permanganate in acid solution #i ,,iv ,action of a ,black ,oxide of ,manganese on ,potassium ,permanganate #bd ,v ,the ,amount of ,nitric ,acid ,neutralized #ca ,,vi ,the ,stability of ,manganese ,dioxide #cd ,,vii ,the ,effect of ,varying ,quantities of ,manganese ,oxide and ,potassium ,permanganate #ci ,,viii ,the ,reduction of ,neutral ,potassium ,permanganate by ,manganese ,oxide at ,ordinary ,temperature #de ,,ix ,action of ,potassium ,permanganate upon a ,manganese ,oxide ,obtained from ,manganese ,dioxide by ,spontaneous ,decomposition #ej ,conclusion ,introduction4 ,the usual laboratory solution of potassium permanganate must be frequently restandardized4 ,a slight loss in strength may be detected after standing even a few days and this change becomes more rapid as the decomposition proceeds4 ,when one looks for the cause of this increase in the rate of the decomposition of the permanganate1 the attention is naturally directed to the brown manganese oxide which separates from the solution4 ,a desire to ascertain whether the presence of this oxide influences the rate of the decomposition suggested the experiments here described4 ,the fact that potassium permanganate may react with certain so-called peroxides with evolution of oxygen1 has long been known and it appeared possible that a similar reaction may take place between manganese dioxide and potassium permanganate4 ,morse and ,allen investigated the reaction between lead dioxide and potassium permanganate and there is embodied in ,allen's dissertation#a a statement of the earlier work in this line with references to the literature on the subject4 #a ,johns ,hopkins ,university #ahib ,they have shown that in the presence of a quantity of dilute nitric acid which is equivalent to the potassium in the potassium permanganate used1 lead dioxide reduces the permanganate to manganese dioxide without itself suffering reduction1 while in the presence of an excess of stronger nitric acid1 e4g4 normal to eight normal1 the lead dioxide is also reduced4 ,the following equations represent the reactions referred to3 ,i1 when the nitric acid is equivalent to the potassium in the potassium permanganate1 #b ,k,mn,o #c ,pb,o ,k,o #c ,pb,o #b ,mn,o #a ,o4 ,,ii1 when the nitric acid is in excess1 #b ,k,mn,o #c ,pb,o ,k,o #c ,pb,o #b ,mn,o #c ,o4 ,the reducing action of manganese dioxide upon potassium permanganate was suspected from the observed increase in the rapidity of the decomposition of potassium permanganate solutions4 ,but only a suggestion of such a reaction could be found in the literature4 ,thnard1#b in #ahef states that manganese dioxide may act upon potassium permanganate either as a reducing agent1 in which act the manganese dioxide is changed to a manganate1 or its influence may be catalytic1 causing the evolution of oxygen4 ,again ,mulder#c in #aheh1 ascribed the decomposition of potassium permanganate solutions to the presence of some potassium manganate4 #b ,comptes ,rendues #db1 #chb #c ,jahresbericht #aheh p4 #eha ,it could not be ascertained that any investigation of this matter had ever been undertaken4 ,it was therefore decided to study the question and it appeared that the most satisfactory evidence could be obtained by measuring the quantity of oxygen which is evolved when potassium permanganate and manganese dioxide are brought together4 ,description of ,apparatus4 ,the apparatus#d employed in this work consists of four parts3 8#a7 a flask1 ,a1 in which the reactions were conducted4 ,a melting point bulb of about #dj cc4 capacity1 the diameter of its neck being #bj mm41 was used for this purpose4 #d ,this apparatus was used by ,allen and described by him4 ,i wish to acknowledge my indebtedness to him for the illustration and description given here which is taken by permission word for word from his dissertation4 ,illustration ,this was closed with a two-hole rubber stopper1 through one hole of which passed3 #b7 ,a small glass tube1 ,,bb1 running up from the flask about #dj cm41 and then bent twice at right angles4 ,one limb of this tube was surrounded by a small ,liebig's condenser1 while the shorter turned down to meet-- #c7 a ,schiff's azotometer filled with mercury and connected at its top with the tube above mentioned4 ,in practice it was found desirable to have a little water on the top of the mercury column4 #d7 ,through the second hole of the rubber stopper closing the flask was passed a short piece of glass tubing bent obliquely just above the stopper and tightly connected with a rubber tube about #ej cm4 long1 ,,dd4 ,this tube was clamped near its lower end with a ,mohr's pinch-cock1 while the upper was connected with the stem of a small funnel1 ,f4 ,when an experiment was to be conducted1 the azotometer ,c1 was connected to the tube1 ,b1 and tied tightly1 a piece of good rubber tubing being used for the connection4 ,the reservoir of the azotometer1 ,m1 was then raised until the mercury had driven out all the air in ,c1 and the stop-cock closed4 ,next the funnel ,f was filled with water1 the pinch-cock closing ,d opened and the water allowed to flow down and drive out all the air in the tube4 ,the latter was then clamped and thus kept full of water4 ,the apparatus being now ready1 the flask ,a1 containing the substances in the desired quantity1 was made fast to ,b and ,d by means of its stopper4 ,the stop-cock of ,c opened4 ,the flask ,a was heated in a water-bath for any desired time1 the oxygen being collected in ,c as fast as it was given off4 ,at the end of the experiment1 all the gases which remained in ,a and ,b were driven over into ,c by lowering the reservoir ,m and opening the pinch-cock at ,d4 ,when this was accomplished the stop-cock of ,c was closed and the gases brought under atmospheric pressure by bringing the mercury in ,c and ,m to the same level4 ,it will be seen that in this gas volume was included the air which ,a and ,b contained at the beginning of the experiment4 ,the oxygen evolved from the contents of the flask was determined thus3 ,after reading off the total volume of air and oxygen and reducing to normal conditions1 the total volume of oxygen was obtained by absorption with phosphorus or pyrogallol1 and from the residual nitrogen could be calculated from the volume of air to be deducted the total volume of gases4 ,the remainder is the volume of oxygen sought40 ,action of manganese dioxide on potassium permanganate in acid solution4 ,three sets of apparatus like the one described were used4 ,the flask of apparatus ,no4 ,i contained manganese dioxide and dilute nitric acid4 ,the flask of apparatus ,no4 ,,ii contained potassium permanganate and dilute nitric acid4 ,the flask of apparatus ,no4 ,,iii contained potassium permanganate and dilute nitric acid and manganese dioxide4 ,the manganese dioxide used in these experiments was precipitated from a solution of potassium permanganate by a dilute solution of manganous sulfate in the manner described on page #cd and then washed and dried at #ajj;,c4 ,an illustration of the proportions in which the different substances were brought together in each of the three flasks is to be found in the following statement of the quantities used in the first experiment4 ,the variations from these proportions occurring in subsequent experiments are noted in the table giving the summary of the results4 ,usually about #aej m4g4 of manganese dioxide were used and the solutions in the three flasks were brought to the same volume by addition of distilled water4 ,experiment ,no4 ,i ,flask ,no4 ,i ,manganese dioxide #aej m4g4 ,n_/#aj nitric acid #ad4bh c4c4 ,mn4 in ,k,mn,o in ,no4 ,,ii or ,no4 ,,iii ,water1 #bg4ab c4c4 ,total solution #da4dj c4c4 ,flask ,no4 ,,ii ,potassium permanganate1 #bj c4c4 #aab4dh m4g4 ,k,mn,o4 ,n_/#aj nitric acid #g4ad c4c4 ,k in ,k,mn,o ,water1 #ad4bf c4c4 ,total solution #da4dj c4c4 ,flask ,no4 ,,iii ,potassium permanganate1 #bj c4c4 #aab4dh m4g4 ,k,mn,o4 ,n_/#aj nitric acid #ba4dj c4c4 ,k ,mn in ,k,mn,o ,manganese dioxide #aej m4g4 ,the nitric acid in ,no4 ,i is calculated to be the same as that remaining free after the potassium of the permanganate in ,no4 ,,iii has been neutralized4 ,it will be clear that the quantities of free nitric acid are the same in flask ,no4 ,i and in flask ,no4 ,,iii provided the potassium of the permanganate is appropriated by the nitric acid4 ,moreover each flask contains the same quantity of manganese dioxide and the volume of the liquid is the same in both4 ,on the other hand flask ,no4 ,,iii contains permanganic acid4 ,this arrangement was selected in order to determine how far the evolution of oxygen was influenced by the action of nitric acid on the manganese dioxide or by the spontaneous decomposition of permanganic acid4 ,it was thought that if more oxygen should be obtained from flask ,no4 ,,iii containing a mixture of permanganate1 manganese dioxide and nitric acid1 than from mixtures ,no4 ,i and ,no4 ,,ii1 the larger volume must be due to the reduction of the permanganate by the manganese oxide4 ,the three flasks after having been filled as described were attached to the apparatus and then all submerged to the same depth in the boiling water of a single glass water-bath4 ,the stop-cocks of the azotometers were then opened and the mercury allowed to fall to within about fifty millimetres of its level in the reservoirs4 ,this difference in level was maintained as nearly as practicable by lowering the reservoirs commenserably with the increase in gas volume4 ,no action could be observed in flasks ,no4 ,i and ,no4 ,,ii during the whole course of the experiment4 ,the contents of flask ,no4 ,,iii however gave off bubbles of oxygen immediately1 the mercury fell in the azotometer and the dark purple of the permanganate solution in flask ,no4 ,,iii became rapidly lighter4 ,within about five minutes it was reduced to a delicate pink but this tint persisted for about ten minutes when it also disappeared4 ,immediately after the disappearance of the permanganate color the solution was filled with a brown oxide which remained for about thirty five minutes when it subsided leaving the supernatant liquid clear4 ,notwithstanding the fact that the color of the permanganate had entirely disappeared and the suspended oxide had subsided within an hour after beginning the experiment1 the flasks in the earlier experiments were allowed to remain for two hours longer4 ,by admitting distilled water through the tube ,d see figure the gas was then forced over into the azotometer4 ,finally1 the oxygen was determined in the manner previously described4 ,the following illustration from the first experiment may serve to show the method of calculating the results4 ,i ,,ii ,,iii ,total air and oxygen #db4fj c4c4 #eb4dj c4c4 #fj4fj c4c4 ,nitrogen after absorption of oxygen #cd4jj c4c4 #dj4ij c4c4 #cg4hj c4c4 ,oxygen #h4fj c4c4 #aa4ej c4c4 #bb4hj c4c4 ,air #gi4h nitrogen #bj4b oxygen ,oxygen of air #bj4b -------------- ---- #h4fj c4c4 #aj4cec c4c4 #i4eg c4c4 ,nitrogen found #gi4h ,oxygen obtained #j4j #a4adg c4c4 #ac4bc c4c4 ,temperature #ba;,c4 ,barometer #gcg mm4 ,oxygen obtained at ,normal #j #a4jcc c4c4 #aa4iac c4c4 ,the #bj c4c4 ,k,mn,o #aab4dh m4g4 #a atom of oxygen #g4ifg c4c4 ,atoms oxygen found ,i ,,ii ,,iii from the molecule ,k,mn,o #j #j4abi #a4dif ,as at the end of the preceding calculation the results are expressed in the table following in terms of oxygen atoms obtained from each molecule of potassium permanganate ,k,mn,o reduced4 ,thus an equivalent of one atom of oxygen from one molecule of potassium permanganate would equal #ae4if_/aeg4fg of the weight of potassium permanganate used in the experiment4 ,this weight divided by the weight of one cubic centimetre of oxygen gives the number of cubic centimetres of oxygen at normal1 equivalent to one atom of oxygen from one molecule of potassium permanganate4 ,the results obtained are tabulated as follows3 ,three-hour determinations4 ---------------------------------------- -------------------------- ,flask ,i ,flask ,,ii ,flask ,,iii ---------------------------------------- -------------------------- ,mn,o ,n_/#aj ,,hno ,k,mn,o ,n_/#aj ,,hno ,k,mn,o ,n_/#aj ,,hno #aej m4g4 ,no4 of #bj c4c4 ,no4 of #bj c4c4 ,no4 of molecules #aab4dh m4g4 molecules #aab4dh m4g4 molecules ---------------------------------------- -------------------------- #a #j4jj #b #j4ac #a #a4die #c #b #j4jj 0 8 #a #a4dic 0 #c 0 #j4ac #c #a4ecb99 0 #d #j4jj 0 #j4ba 0 #a4dff 0 #e #j4jc 0 #j4aj 0 #a4dfg 0 #f #j4jb 0 #j4be 0 0 #g #j4jf 0 #j4jh 0 #a4ebf99 0 #h #j4jd 0 #j4ae 0 #a4ebg 0 #i #j4jd 0 #j4aa 0 #a4ejd 0 #aj 0 #j4bj 0 #a4ejd 0 #aa #j4jc 0 #j4ad 0 #a4eaf 0 #ab #j4jj 0 #j4ah 0 #a4ebd 0 #ac #j4jc 0 #j4be 0 #a4eei99 0 #ad #j4je 0 #j4bf 0 #a4egd 0 #ae #j4jb #a #j4cb #b #a4eeb #b #af #j4jc 0 #j4ca 0 #a4ehc8 0 #ag #j4jd 0 #j4ca 0 #a4eab 0 #ah #j4ja 0 #j4cb 0 #a4dff 0 #ai #j4jj 0 #j4ah 0 #a4dab 0 #bj #j4ja 0 #j4cf 0 #a4daa 0 #ba #j4jf 0 #j4bb 0 #a4djb 0 #bb #j4jj 0 #j4cj 0 #a4die99 0 #bc #b #j4jh #c #a4dfi #c #e;,fifty minute determinations #bd #j4jd #a #j4jf #b #a4efd #b #be #j4jd 0 #j4aa 0 #a4dia 0 #bf #j4je 0 8 0 #a4eab 0 #bg #j4jc 0 #j4je 0 #a4ecb 0 #f;,fifteen minute determinations #bh #j4je #a #j4jh #b #a4cdj #b #bi #j4jd 0 #j4je 0 #a4cbe 0 #cj #j4jf 0 #j4je 0 #a4cce 0 #ca #j4jj 0 #j4jj 0 #a4cdg 0 #cb #j4jc 0 #j4jc 0 #a4dab 0 #cc #j4jb #b #j4jb #c #a4cfc #c #cd #j4jb 0 #j4jf 0 #a4cgg 0 #ce #j4jj 0 #j4jb 0 #a4cfc 0 #e ,this marked the time when the oxides first settled1 leaving a colorless supernatant liquid4 #f ,this marked the time when the solution was first decolorized4 ,inspection of the table will show that whether the oxygen were determined immediately after the subsidence of the oxides 7i4e4 after fifty minutes7 or after three hours the results obtained are practically the same4 ,the tendency of the potassium permanganate to lose strength made the frequent preparation of new samples advisable4 ,wherever a new sample has been used in the course of the experiments1 the fact has been noted in the table by an asterisk4 ,it will be noticed that where a new solution is used the figures for flask no4 ,,iii are immediately larger and nearer to one and one half atoms of oxygen from each molecule of potassium permanganate4 ,a phosphorus gas-pipette was used for the absorption of the oxygen in all the experiments the results of which are embodied in the foregoing table4 ,in subsequent experiments an alkaline solution of pyrogallol was employed4 ,it is now known that the variation in the composition of the manganese oxide in use had some influence upon the results4 ,it has also been found that the manganese dioxide prepared by the reduction of permanganate by manganese sulphate is much less stable than was supposed at the time this work was begun4 ,the dioxide prepared in this way begins immediately to lose oxygen spontaneously but recovers the same in the presence of an excess of potassium permanganate4 ,in the light of these facts it is easy to understand why lower results were obtained when the oxygen was determined immediately after the disappearance of the color of the permanganate and before the suspended oxide had subsided4 ,it appears that the manganese oxide employed in these experiments was not1 as was supposed at the time1 the dioxide but one containing a smaller proportion of oxygen4 ,if such is the case the first action of the permanganate upon it would be to replace the oxygen which had been lost4 ,the reduction of the remaining permanganate would then probably be in accordance with the equation1 #b ,k,mn,o #c ,mn,o #b ,k,o #e ,mn,o #a ,o ,at the time when the permanganate color disappears1 all of the manganese is in the dioxide condition and the further evolution of oxygen1 which is shown by the preceding experiments to take place during the subsidence of the suspended oxides1 is due to a partial reduction of this manganese4 ,therefore the relation of the reduction of the manganese oxide below the ,mn,o condition before the treatment with permanganate to the reduction which follows the disappearance of the permanganate color will determine whether the oxygen evolved shall be more or less than one and one half atoms to each molecule of permanganate4 ,neither variations in the quantities of nitric acid used 7from two to three molecules in ,no4 ,,iii7 nor the very slight variations in the amount of manganese dioxide used1 seem to affect appreciably the amount of oxygen obtained4 ,it appears that the action of manganese dioxide on potassium permanganate is the same as that of lead superoxide#g in the presence of very dilute nitric acid4 ,both reduce it to manganese dioxide with the evolution of one and one half atoms of oxygen to each molecule of the permanganate4 #g ,allen's thesis4 ,the evolution of oxygen from flask ,no4 ,i containing manganese dioxide and nitric acid is very slight4 ,from flask ,no4 ,,ii containing potassium permanganate and one equivalent nitric acid1 it is also slight but usually greater than from flask ,no4 ,i4 ,the differences are much greater in the case of those determinations in which the heating of the flask was continued for three hours and in this fact is to be found further evidence of the reducing action of manganese dioxide on potassium permanganate4 ,the possibility of a reaction analogous to that between potassium permanganate and lead dioxide in the presence of strong nitric acid seems to be excluded by the fact that the higher oxides of manganese may be prepared in the presence of concentrated nitric acid4 ,action of a ,black ,oxide of ,manganese on ,potassium ,permanganate4---- ,as an analysis of the manganese dioxide showed the probable presence of some manganese in the manganous condition1 a sample was treated on the water-bath for some days with dilute nitric acid while distilled water was added from time to time to keep the dilution nearly constant4 ,this was done for the purpose of determining whether the manganous manganese might not be extracted in the form of manganese nitrate4 ,the light brown oxide which was used in the previous experiments had been prepared by adding a dilute solution of manganous sulphate to a hot solution containing potassium permanganate in excess and dilute nitric acid4 ,no analysis of the oxide thus prepared was made at the time of its preparation1 but it has been shown by the work of others that the oxide must have had at that time a composition as regards the relation of manganese to oxygen1 very nearly equivalent to that of ,mn,o4 ,during the course of the experiments previously recorded1 a determination of the ratio of the manganese to the available oxygen in the compound was made and found to be as #a4jc 3 #a4jj ,the substance gave #ed4fi percent manganese and #ae4dd percent available oxygen4 ,a second analysis made some weeks later gave a ratio of manganese to available oxygen of #a4jf3 #a4jj4-- ,the substance gave #ed4gf percent manganese #ae4jb 0 available oxygen4 ,the manganese was determined by the method of ,gibbs#h and the available oxygen by oxalic acid and potassium permanganate4 #h ,silliman's ,am4 ,j4 ,science 7#b7 #dd4baf ,it was this oxide which was treated with nitric acid in the manner described4 ,in the course of this treatment the light brown color changed to black and the oxide became heavier4 ,the dilute nitric acid in which the oxide had been digested was found to contain manganous manganese1 but analysis of the black product showed that the oxide had suffered a still further reduction4 ,the ratio of manganese to available oxygen was found to have risen from #a4jf3 #a4jj to #a4aeg3 #a4jjj4 ,the analytical data are given below3-- ,the substance gave #fj4di percent manganese #fj4df 0 0 and #ae4bc percent oxygen #ae4ai 0 0 ,this ratio would correspond very nearly to a compound having the composition ,mn,o#f,mn,o but it is by no means certain that the reducing action of nitric acid was finished4 ,the action of this oxide on potassium permanganate was determined under the same conditions as in the case of the brown oxide as described on page #ad4 ,the following illustration of the proportions used is taken from the first experiment4 ,experiment ,no4 ,i ,flask ,no4 ,i ,manganese oxide1 black1 #aej m4g4 ,n_/#aj nitric acid #ad4ic c4c4 ,mn in ,k,mn,o in ,no4 ,,ii or ,no4 ,,iii ,water #bg4df c4c4 ,total solution #db4ci c4c4 ,flask ,no4 ,,ii ,potassium permanganate #bj c4c4 #aag4ga m4g4 ,n_/#aj nitric acid #bb4ci c4c4 ,k and ,mn in ,k,mn,o ,total solution #db4ci c4c4 ,flask ,no4 ,,iii ,potassium permanganate #bj c4c4 #aag4ga m4g4 ,n_/#aj nitric acid #bb4ci c4c4 ,k and ,mn in ,k,mn,o ,manganese oxide1 black #aej m4g4 ,total solution #db4ci c4c4 ,the first two results are from experiments in which the action was stopped at the first loss of the color of potassium permanganate4 ,the last two are the results from experiments in which the action was stopped after the oxide had settled leaving a clear colorless supernatant liquid4 ,the amount of oxygen given off in any one case is expressed in the table as the number of atoms of oxygen derived from each molecule of potassium permanganate1 as follows3 ,a ,n_/#aj nitric acid4 ,no4 of molecules4 ---------------------------------------- ----------------------- ,flask ,i ,flask ,,ii ,flask ,,iii ---------------------------------------- ----------------------- ,black ,potassium ,potassium oxide ,a permanganate ,a permanganate ,a #aej m4g4 #bj c4c4 #bj c4c4 #aag4ga m4g4 #aag4ga m4g4 ---------------------------------------- ----------------------- #a #b hours4 #j4jj #b #j4ah #c #a4ccg #c #b #b hours #j4jb 0 #j4bd 0 #a4cce 0 #c #b hours #j4jb 0 #j4dd 0 #a4djb 0 #d #d hours #j4jj 0 #j4ee 0 #a4cfb 0 ,the volume of the oxygen evolved is considerably smaller than that obtained when the brown oxide was used4 ,it is nevertheless larger than could have been evolved if all of the manganese had been left in the dioxide condition at the close of the experiment4 ,this fact indicates that there was a slight reduction of the manganese dioxide after the disappearance of the color of the permanganate4 ,that such a reduction of manganese dioxide does take place will be made apparent by a comparison of the results of the first two experiments in which the oxygen was measured soon after the color of permanganate had disappeared1 with the results of the last two experiments in which the oxygen was determined after a longer interval4 ,it will be noticed in this as in the series of experiments with the brown oxide that the rate of the evolution of oxygen liberated in flask ,no4 ,,ii increases with the time of heating4 ,the ,amount of ,nitric ,acid neutralized4 ,a few experiments were made to determine how much nitric acid is neutralized under the conditions which prevailed in the foregoing experiments4 ,i4 ,the flask contained brown oxide #aej m4g4 ,n_/#aj nitric acid #f4ih c4c4 and was heated for three hours in the water-bath4 ,acid neutralized #d4ea c4c4 #fd4fj percent4 ,,ii4 ,the flask contained brown oxide #aej m4g4 ,n_/#aj nitric acid #f4ih c4c4 and was heated for #ej minutes in the water-bath4 ,acid neutralized #c4ji c4c4 #dd4bj percent4 ,,iii4 ,the flask contained brown oxide #aej m4g4 ,n_/#aj nitric acid #g4df c4c4 and was heated for fifty minutes in the water-bath4 ,acid neutralized #c4af c4c4 #db4cj percent4 ,,iv4 ,the flask contained brown oxide #aej m4g4 ,n_/#aj nitric acid #g4df c4c4 and was heated for #ae minutes in the water-bath4 ,acid neutralized #b4gf c4c4 #cg4j percent ,v4 ,the flask contained brown oxide #aej m4g4 potassium permanganate #bj c4c4 #aab4dh m4g4 ,n_/#aj nitric acid #f4ih c4c4 7 #b molecules for each molecule of ,k,mn,o7 and was heated for three hours in the water-bath4 ,acid neutralized #j4ce c4c4 #e4j percent4 ,,vi4 ,repetition of ,no4 ,v4 ,acid neutralized #j4dd c4c4 #f4c percent4 ,,vii4 ,the flask contained brown oxide #aej m4g4 potassium permanganate the same as in numbers ,v and ,,vi and was heated for #ae minutes in the water-bath4 ,acid neutralized #e4b percent4 ,,viii4 ,repetition of ,no4 ,,vii ,acid neutralized #d4j percent ,,ix4 ,the flask contained black oxide #aej m4g4 ,n_/#aj nitric acid #ad4ic c4c4 and was heated for two and one fourth hours in the water-bath4 ,acid neutralized #d4hg c4c4 #cb4df percent4 ,x4 ,repetition of ,no4 ,,ix4 ,acid neutralized #ch4aj percent4 ,,xi4 ,the flask contained black oxide #aej m4g4 potassium permanganate #bj c4c4 #agg4ga m4g41 ,n_/#aj nitric acid #bb4ci c4c4 7 #b molecules for each molecule of ,k,mn,o7 and was heated four and one half hours in the water bath4 ,acid neutralized #ajj4jj percent4 ,no definite conclusions can be drawn from these neutralization experiments since it is well known that manganese oxides prepared as were those used in these experiments always contain some1 though probably not a constant quantity of alkali4 ,it is stated by ,bemmelen#i that manganese dioxide decomposed the salts of the alkalies with liberation of acid4 #i ,j4 fr ,prak4 ,ch4 7#b7 #bc1 #cbd-cgi4 ,the ,stability of ,manganese ,dioxide4 ,having found in the course of the work already described that manganese dioxide prepared in the wet way is much less stable than was supposed1 it was decided to make some experiments upon the spontaneous decomposition which it undergoes4 ,to this end a fresh sample was prepared in the following manner4 #aj grams of potassium permanganate were dissolved in #ejj c4c4 of distilled water and the solution allowed to settle for one day4 ,the liquid was then filtered through glass wool1 heated to #fe;,c4 and treated with #cbj c4c4 ,n_/#aj nitric acid1 having also a temperature of #fe;,c4 #bj4e grams of manganous sulphate dissolved in #b4e litres of water heated to #fe;,c1 were now added1 with stirring1 to the acidified solution of potassium permanganate4 ,the precipitate was allowed to settle and the supernatant liquid which still retained the permanganate color1 decanted4 ,the residue was then treated with water1 stirred and allowed to settle4 ,the water was decanted and the oxide filtered4 ,the filter used consisted of two platinum cones between which was placed a small paper filter which did not quite reach to the edge of the outer cone4 ,this filter was placed in the bottom of a glass funnel and the oxide poured upon it4 ,the oxide was repeatedly washed with distilled water and then transferred to a porous plate4 ,it was afterwards heated for several hours to a temperature of #fe;,c4 ,at this temperature it was found impracticable to bring the oxide to a constant weight1 but this fact was no serious obstacle in the way of the subsequent work since it was only desired to ascertain what changes take place in the ratio of the manganese to the available oxygen4 ,the manganese was determined by the method of ,gibbs and the available oxygen by oxalic acid and potassium permanganate4 ,an analysis of the oxide made shortly after its preparation in the manner described1 gave #ea4ih percent ,manganese #ea4hf pr4 ct4 #ea4gd 0 #ad4hcf percent ,oxygen #ad4hcg 0 #ad4hci 0 showing a ratio of manganese to available oxygen of #a4jah 3 #a4jjj4 ,the above analysis was made ,may #a1 #ahib4 ,the oxide was then placed in a glass-stoppered weighing bottle and allowed to stand until ,november4 ,an analysis made on the tenth day of the latter month gave a ratio of manganese to available oxygen of #a4aih 3 #a4jjj corresponding very closely to a composition ,mn,o#e,mn,o1 in which the calculated ratio is #a4bjj 3 #a4jjj ,six month later 7,april #bj1 #ahic7 an analysis of the same material showed a ratio of manganese to available oxygen of #a4cjj 3 #a4jjj ,this result was confirmed ,m ,walker who made repeated analyses of the substance at the same time4 ,another sample of manganese oxide was prepared in the same manner as that used in the previous experiments and placed under water4 ,an analysis made after ,eight days gave a ratio of ,mn 3 available ,o #a4jac 3 #a4jjj ,twenty 0 0 0 0 0 0 0 0 #a4jcg 3 #a4jjj ,forty three 0 0 0 0 0 0 0 0 #a4jdj 3 #a4jjj ,the results here recorded clearly indicate that the brown oxide of manganese which is prepared by the reduction of potassium permanganate by manganese sulphate undergoes a spontaneous decomposition involving a loss of oxygen4 ,this loss of oxygen or the effect of varying conditions upon this decomposition of manganese dioxide is now being investigated by ,m ,walker of this laboratory4 ,the ,effect of ,varying ,quantities of ,manganese ,oxide on ,potassium ,permanganate4 ,the following experiments were made for the purpose of determining the effect of varying quantities of manganese oxide on the time required for the reduction of potassium permanganate4 ,a4 ,in the presence of nitric acid4 ,the ratio of manganese to available oxygen in the material used for these experiments was determined and found to be #a4jah 3 #a4jjj ,the experiments were conducted after the same manner as those previously described4 ,different portions of the manganese oxide were weighed out and treated in the flasks used in the previous experiments with the quantities of permanganate which were found by calculation to have the desired molecular ratios to the oxide4 ,a quantity of ,n_/#aj nitric acid equivalent to the potassium of the potassium permanganate was added4 ,the flasks were then immersed in the bath of boiling water and the time required for the disappearance of the permanganate color noted4 ,the ratios of the oxide to the permanganate and the times required for the reduction of the latter are embodied in the following table4 ,molecular ,ratio ,oxide to ,k,mn,o #a3a #b3a #c3a #d3a #e3a #f3a #g3a ,time of decolorization in minutes #a 0 #abj #fh #b 0 #aaj #fe #c 0 #aej #fe #d 0 #aej #hj #e 0 #abj #ge #f 0 #abj #ge #g 0 #age787 #gh #ec #h 0 #afj #gi #ed #i 0 #ade #da #cj #aj 0 #abj #ej #cf #aa 0 8 #dg #cb #ab 0 #aaj #cg #cj #ac 0 #fd #ajbj787 #bj787 #ad 0 #gb #e787 #e787 #ae 0 #he #e787 #e787 #aj ,decolorized before time was taken4 ,the results appearing in the table on the same horizontal lines are those of experiments made simultaneously1 that is1 the flasks in these experiments were immersed at the same time and in the same water-bath4 ,these1 that is the results appearing on the same horizontal line1 and these only are comparable1 since it was found that very slight differences in the temperature of the bath were of great influence on the length of time required for the reduction of the permanganate4 ,it is clear that the rate of the reduction of the permanganate is greatly increased by increasing the quantity of the manganese oxide4 ,after reduction of the permanganate1 the contents of the flasks were in every case filtered and the filtrate tested by ,crum's reaction for the presence of manganese4 ,no manganese was found4 ,the absence of manganese in the filtrate shows that the reduction of the permanganate was not due to the formation of manganese nitrate1 though it will be clear from the results of subsequent experiments that the presence of nitric acid exerts an influence on the rate of the reduction4 ,b4 ,in neutral solution4 ,the condition were the same as under ,a1 except that the nitric acid was omitted4 ,those flasks containing potassium permanganate and one1 two and seven molecular equivalents respectively of the manganese oxide were immersed in the water-bath as before4 ,no4 ,i containing one molecule of oxide and one molecule ,k,mn,o was reduced in #eg hours ,no4 ,,ii containing two molecules of oxide and one molecule ,k,mn,o was reduced in #ce hours ,no4 ,,iii containing seven molecules of oxide and one molecule ,k,mn,o was reduced in #b hours ,c4 ,in alkaline solution4 ,the conditions were the same as under ,b1 except that five molecules of potassium hydroxide were added for each molecule of the permanganate4 ,no4 ,i containing one molecules of oxide for each molecule ,k,mn,o was reduced in #ia hours4 ,no4 ,,ii containing two molecules of oxide for each molecule ,k,mn,o was reduced in #ee787 hours4 ,no4 ,,iii containing seven molecules of oxide for each molecule ,k,mn,o was reduced in #aj hours4 ,it appears that potassium permanganate is less easily reduced by manganese oxide in neutral than in acid solutions and in alkaline that in neutral solutions4 ,the ,reduction of ,neutral ,potassium ,permanganate by ,manganese ,oxide at ,ordinary ,temperature4 ,in these experiments1 the manganese oxide used was prepared in the same manner as that in which the proportion of manganese to available oxygen was found immediately after its preparation to be #a4jah 3 #a4jjj ,it was dried for several days at #fe;,c41 but for almost a month after its preparation was not used4 ,hence1 what the ratio of the manganese to the oxygen at the time when the permanganate was treated with it1 is quite uncertain4 ,it however appears probable from the subsequent experiments on the instability of manganese dioxide at #fe;,c4 that the ratio of manganese to available oxygen must have been at about #a4je3 #a4jj corresponding to a formula ,mn,o#bj,mn,o4 ,two solutions of permanganate were made1 filtered through glass wool and standardized4 ,solution ,a4 ,a cubic centimetre of this was found to be equivalent to #e4bgh m4g4 iron in the ferrous condition4 ,solution ,b4 ,a cubic centimetre of this was found to be equivalent to #ad4cgi m4g4 iron in the ferrous condition4 ,three #bej c4c4 portions of each of the solutions ,a and ,b were placed in clean glass-stoppered bottles4 ,these bottles were labelled 8a01 8a0 and 8a0 8b01 8b0 and 8b04 8a0 contained #bej c4c4 potassium permanganate each cubic centimetre of which was equivalent to #e4bgh m4g4 ,fe4 ,it was closed and put away in the dark and allowed to stand from ,june fourteenth until the fourteenth of the following ,october4 ,its strength was then determined and found to have declined #j4gb percent4 8a0 contained the same quantity of the same permanganate solution as 8a0 and it was closed on the same date and placed in mildly diffused light until ,october fourteenth4 ,an analysis on the latter date showed that its strength had also declined #j4gb percent4 8a0 contained the same quantity of the same permanganate solution as 8a0 and 8a0 and to this was added #j4e gram of the manganese oxide previously referred to4 ,the bottle was then closed and placed in diffused light beside 8a04 ,an analysis1 ,october fourteenth showed that its strength had declined #cd4fb percent4 8b0 contained potassium permanganate each cubic centimetre of which was equivalent to #ad4cgi m4g4 ,fe4 ,it was closed and put away in the dark beside 8a04 ,an analysis ,october fourteenth showed that its strength had declined #a4ga percent4 8b0 contained the same quantity of the same permanganate as 8b04 ,it was closed and placed in mildly diffused light beside 8a04 ,an analysis ,october fourteenth showed a decline in strength of #b4da percent4 8b0 contained the same quantity of the same permanganate as 8b0 and 8b04 ,to it was added #j4e grams of the manganese oxide4 ,the bottle was closed and placed in diffused light beside 8a01 8a01 and 8b04 ,an analysis1 ,october fourteenth showed a decline in strength of #gh4hf percent4 ,the conclusions to be drawn from the foregoing results are 7#a7 that dilute solutions of potassium permanganate are more stable both in diffused light and in darkness than the more concentrated ones1 and 7#b7 that the presence of manganese oxides hasten to an enormous degree the reduction of potassium permanganate even at summer temperatures4 ,it will also be observed that this reducing action of the manganese oxide is greater in the stronger than in the more dilute solutions4 ,it should be remarked that the summer of #ahib in which these experiments were made1 was one of unusual heat4 ,action of ,potassium ,permanganate upon a ,manganese ,oxide ,derived from ,manganese ,dioxide by ,spontaneous ,decomposition4 ,the oxide used in these experiments was one which had been prepared in the manner heretofore described by adding manganese sulphate to an excess of potassium permanganate4 ,soon after its preparation the ratio of manganese to available oxygen in it was found to be #a4jah 3 #a4jjj ,at the time when it was used in these experiments1 the ratio of manganese to available oxygen was found to be #a4aih 3 #a4jjj ,corresponding very nearly to the ratio of manganese to available oxygen in ,mn,o#e,mn,o4 ,experiment ,i4 #bcj m4g4 of the oxide was treated with the quantity of permanganate calculated to be necessary for its oxidation to manganese dioxide4 ,the mixture was kept at a temperature of #bb;,c4 until the color of the permanganate disappeared4 ,this required about ten hours4 ,an analysis of the oxide then gave a ratio of manganese to available oxygen #a4jbg 3 #a4jjj ,experiment ,,ii ,a repetition of experiment ,i4 ,an analysis of the oxide after decolorization of the permanganate gave a ratio of manganese to available oxygen of #a4jbb 3 #a4jjj ,experiment ,,iii ,the conditions are the same as in the preceding experiments except that twice the amount of permanganate calculated for the conversion of the oxide into manganese dioxide was added4 ,an analysis of the residue after decolorization gave a ratio of manganese to available oxygen of #j4iid 3 #a4jjj ,experiment ,,iv ,a repetition of experiment ,,iii4 ,an analysis of the residue gave a ratio of manganese to available oxygen of #j4iie 3 #a4jjj ,experiment ,v ,a repetition of experiments ,,iii and ,,iv4 ,the ratio of manganese to available oxygen in the residue was #j4iie 3 #a4jjj4 ,the foregoing results indicate 7experiments ,,iii1 ,,iv1 and ,v7 that the oxygen lost spontaneously by manganese dioxide prepared in the wet way1 is fully recovered when the reduced oxide is treated with excess of potassium permanganate4 ,the ratio of the manganese to the available oxygen was determined in the following manner4 ,the contents of the flask were filtered through asbestos and the flask and the precipitate washed with cold water4 ,the contents of the filter were then returned to the flask and treated with an excess of a standard solution of oxalic acid and dilute sulphuric acid4 ,after reduction the excess of the oxalic acid was determined by a standard solution of potassium permanganate4 ,the solution was then filtered1 well washed and the manganese in the filtrate precipitated by the method of ,gibbs4 ,from the total amount of manganese found1 there was deducted the quantity which was introduced in determining the excess of oxalic acid by potassium permanganate4 ,summary of ,conclusions-- ,i ,potassium permanganate in weakly acid1 in neutral1 and in alkaline solutions1 is reduced by manganese dioxide which has been prepared in the wet way1 with evolution of one and one half atoms of oxygen for each molecule of the permanganate4 ,in other words1 the permanganate is reduced to manganese dioxide4 ,,ii ,this reduction is most rapid in acid and slowest in alkaline solutions4 ,,iii ,the rate of reduction is greatly increased by increasing the proportion of manganese dioxide4 ,,iv ,in concentrated solutions of potassium permanganate1 the reduction by manganese dioxide is relatively more rapid than in dilute4 ,v ,manganese oxide1 prepared in the wet way i4e4 by the addition of manganese sulphate to a hot solution containing an excess of permanganate1 has the composition ,mn,o as regards the ratio of manganese to available oxygen4 ,,vi ,this oxide is unstable4 ,it loses oxygen spontaneously even at ordinary temperatures4 ,,vii ,the oxygen which is thus lost is recovered when the oxide is again treated with an excess of potassium permanganate4 ,,viii ,it is suggested that a partial explanation of the reduction of potassium permanganate by manganese oxide may be found in the instability of the latter2 in other words that the reduction may consist in alternate reduction and reoxidation processes4 ,but when the rapidity of the reduction is taken into account1 it seems probable that a reaction analogous to that between permanganic acid and hydrogen superoxide must also take place4 ,arthur ,john ,hopkins was born ,september #bj1 #ahfd in ,bridgewater1 ,massachusetts4 ,receiving his preparation for college in the public schools of that town1 he entered ,amherst ,college in #ahha and graduated with the degree of ,a4 ,b4 in #ahhe4 ,the five years following were spent in teaching in the ,states of ,massachusetts and ,new ,york4 ,he entered the ,johns ,hopkins ,university in #ahij1 was assistant in the quantitative laboratory of that university during the academic year of #ahia-ib1 and the following year was appointed ,fellow in ,chemistry4