118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. THE CATALYTIC DECOMPOSITION OF HYDROGEN PEROXIDE SOLUTION BY BLOOD CHARCOAL. BY J. B. FIRTH, D.Sc., F.I.C., AND F. S. WATSON, M.Sc. ( A Paper read before THE FARADAY SOCIETY, Monday, November 12fh, 1923, SIR ROBERT ROBERTSON, K.B.E., F.R.S., PRESIDENT, in the Chair.) Received October 3 rd, I 9 2 3. I t has been shown already by many investigators that hydrogen peroxide is readily decomposed by a great variety of substances with the liberation of oxygen. Fillipi showed that all powders decompose hydrogen peroxide, the velocity of decomposition being proportional to the exposed surface of the added powder and independent of the concentration of the hydrogen peroxide.Lemoine found that charcoals obtained in the de- composition of wood, coconut and sugar are efficient catalysts of hydrogen peroxide ; the catalytic effect being apparently correlative with their sorptive power for gases. Clayton showed that hydrogen peroxide does not vola- tilise appreciably from its aqueous solutions at 50" to 60" C., and the rate of decomposition is not affected by stirring. Rideal and Thomas showed that hydrogen peroxide is decomposed by Fuller's earth. The catalytic activity in the decomposition of the hydrogen peroxide is not dependent on the adsorptive power ; it would appear that the iron content of the Fuller's earth may be the governing factor.On applying the equation for a uni- molecular surface reaction the velocity coefficient is constant for a given sample of Fuller's earth. The authors5 have shown that ordinary pure sugar carbon gives rise to only very slight decomposition of hydrogen peroxide in aqueous solution but the rate and extent of the decomposition increases considerably as the activity of the carbon is increased, and also with rise of temperature. The activity of the carbon gradually decays during the reaction. the authors describe experiments with carbons from other carbohydrates in which it is shown that the rate of de- composition varies considerably with the different carbons, but the funda- mental difference is in the initial activity. The activity falls rapidly after the first few minutes, becoming ultimately very slight, even though the solution contains a fair proportion of undecomposed hydrogen peroxide. The object of the present investigation was to study the decomposition of hydrogen peroxide solution by blood charcoal, before and after activation treatment. Whereas in previous experiments relatively pure carbons were used, in the present case the charcoal contains appreciable quantities of impurity, mair,ly iron.Experiments were therefore carried out in order to determine as far as possible the influence of this impurity on the rate of decomposition of the hydrogen peroxide. Arch. Farm. sperim., 1907, 6, 363. 3 Trans. Faraday SOC., 1916, 11, 164. 5 Trans. Clacm. SOC., 1923, 123, 1750. In a further paper Comfit. rend., 1916, 162, 725.your. SOC. Chem. Ind., 1g23,W, 37IT. 4 Trans. Chem. SOC., 1922,121,2119. 601602 THE CATALY'TIC DECOMPOSlTION OF HYDROGEN Exferimenta 1. The blood charcoal as supplied gave on ignition 8-82 per cent. of ash which consisted almost entirely of iron oxide. The charcoal was digested for several days with hot aqua regia, after which treatment the ash content was 7-30 per cent. It was then subjected to a prolonged treatment with aqua regia, for about a month, the ash content becoming 6-32 per cent. A quantity of this charcoal was then further treated with bromine for several days, after which the ash content was 5.79 per cent. I n each case all soluble material was extracted by washing with boiling dis- tilled water until the filtrate showed no indication of iron with potassium sulphocyanide, nor of halogen with silver nitrate solution.A sample of the purified charcoal was taken after each of the four purification processes given above. The charcoal was thoroughly dried by heating in an air oven at 1 2 0 O C. and the catalytic activity determined in each case. The experimental details are exactly as described in our first paper (Zooc. cit.). The hydrogen peroxide solution used contained 240-5 C.C. of available oxygen per 25 C.C. of solution. 0.~5 grams of the charcoal and 25 C.C. of the hydrogen peroxide solution were used in each experi- ment, and the temperature of experiment was 18" C. The reaction velocity coefficients are calculated from the equation for a unimolecular surface reaction dx/dt = K(a - x) to the Naperian base and the minute as unit of time.The volumes are, in all cases, corrected to N.T.P. and are ex- pressed in C.C. The volumes of oxygen liberated were determined at intervals ranging from 30 seconds to half an hour according to the rate and stage of the reaction. The results obtained are given in Table I. TABLE r. Time in Minutes. 0'5 3 6 24 51 66 10.5 I I2 I22 (1) Charcoal as Received. Volume of Oxygen in C.C. K X 103. 12'80 I I 'go 8-93 7.16 4'49 10'10 2-12 - - - (2) Charcoal Purified by Digestion with Aqua Regia for Several Days. Volume of Oxygen in C.C. 3'2 6.1 14'8 24.0 39'5 60.7 100.g 111.8 110'2 112'2 ____ K X I$. I 1.60 9-16 7-60 6.49 5-26 4'63 4'03 2-60 2-23 11'20 (3) Charcoal Purified by Digestion with Aqua Regia for a Month.Volume of Oxygen in C.C. 2.8 5'2 12'0 21'0 35'4 98.2 IL 5.1 127.7 58'5 122'2 __ __ K x 103. - . 10'20 9'40 7-40 6.62 5 '04 4'47 2 '93 2.6 I 5-76 3'78 (4) Charcoal Purified by Bromine Treatment. Volume of Oxygen in C.C. _ _ _ ~ 1 '9 4'8 10'0 16% 30.0 52'5 92 -1 102'6 126.8 132'3 K x I@?. 6.80 8-70 6-16 5 '23 4-82 4'45 4-11 3'66 3-10 2-84 From the above table it would appear that the initial rate of decomposi- tion is decreased by continued treatment with aqua regia and subsequent bromine treatment ; whilst on the other hand the total decomposition with- in the period of observation is appreciably increased by this treatment. The decomposition by all three purified charcoals is approximately double that of the original charcoal, after the reaction has proceeded sixty-six minutes.In the case of the charcoal treated with bromine, the maximum rate is not developed in the first half minute as in the other cases. I t seems possible that the decrease in the initial velocity with the purifiedPEROXIDE SOLUTION BY BLOOD CHARCOAL 603 Charcoal Activated by Method 111. charcoals might be due to the retention of a trace of the purifying agent, either free or combined with the iron, for although no halogen could be detected in the final washings during the purification of the charcoal, a slight trace of halogen was detected in the resulting ash and this was most pronounced after the bromine treatment. I n all subsequent experiments the charcoal was purified by digesting the original charcoal for about a month with aqua regia, as previously de- scribed.The resulting purified charcoal was then activated by one of the following methods :- I. The finely divided charcoal was introduced into a quartz flask and heated in a vacuum for two hours at 600' C., allowed to cool in a vacuum and then 0.25 gram of the charcoal rapidly weighed out. 11. As in I. except that the temperature of activation was gooo C. 111. A quantity of charcoal activated as in I., was treated with K/IO iodine solution in chloroform, in the proportion of 25 C.C. of the solution per gram of charcoal, for twenty-four hours. The charcoal was then filtered off, transferred to a silica dish and gently heated until practically the whole of the iodine had been volatilised. The charcoal was then shaken several times with an alcoholic solution of potassium hydroxide and boiled with distilled water until, on filtering, the filtrate showed no opalescence with silver nitrate solution.The resulting charcoal was finally heated in a vacuum in a quartz flask at about 600' C. for two hours and 0-25 gram of the charcoal rapidly weighed out on cooling to room temperature. IV. Finely divided charcoal was first treated as in I1 then as described in III., except that the final heating in a vacuum was carried out at gooo C. The results obtained for the four charcoals activated as described above are given in Table 11. 2 5 C.C. of the hydrogen peroxide solution contained 242'5 C.C. of available oxygen and 0.25 gram of charcoal was used in each case. Charcoal Activated by Method IV.TABLE 11. Vo!ume of Oxygen in C.C. Charcoal Activated 1 bv Method I. K X I d Time I - Volume of Oxygen in C.C. in K X 103. 0'5 3 6 24 30 60 I I2 I 22'6 39'5 87'4 129.2 157'7 173'3 175.0 175'7 25'5 42'3 100.6 149'3 165'1 173'5 176.1 177'8 85 '00 77-20 64-70 5 5'05 37'94 22'70 18-50 9'33 96'40 83'30 77'60 69'21 41-33 22-75 18-66 9'56 Charcoal Activated by Method 11. l- I Volume of Oxygen in C.C. K x IS. 162'60 147.20 102'80 70.15 41'51 22-77 18-81 9'60 81'0 126.8 148.2 I 66% 174.8 177'4 180.8 258.80 176.60 107'13 68'36 42.13 23.09 19.04 9-91 The object of the next series of experiments was to determine the in- fluence of the presence of the iron in the blood charcoal on the catalytic activity. I n order to do this an '' artificial blood charcoal " was prepared from cane sugar as follows : To a solution of cane sugar, containing a weighed amount of sugar, a definite amount of ferric chloride was added.The iron was then precipitated by the addition of excess of ammonium hydroxide. The resulting liquid was then evaporated to dryness, the liquid604 THE CATALYTIC DECOMPOSITION OF HYDROGEN Time in Minutes. 0.5 3 6 24 30 60 I I2 being repeatedly stirred and the product carbonised at as low a temperature as possible. The resulting charcoal was then digested with hot aqua regia for several days, then filtered off and boiled with distilled water until, on filtering, the filtrate gave no test for iron with potassium sulphocyanide and no opalescence with silver nitrate. Two samples of such charcoals were prepared. No. I containing 1-46 per cent.of ash and No. 2 yielding 9.10 per cent. ash. The catalytic activity of these charcoals was then determined as de- scribed in previous experiments ; first after drying at 1 2 0 ~ C. and then activated by methods I. or 11. as given above. The strength of the hydro- gen peroxide solution was equivalent to 243.4 C.C. of available oxygen. The results obtained are given in Table 111. TABLE 111. No. I Artificial Blood Charcoal. - Dried at I?OO C. Activatedat 6oo°C Oxygen in C.C. Oxygen in C.C. Volume of Volume of 3'7 7'9 7'0 11.3 13-1 18-1 19.2 24-6 26-5 33'7 36'7 44'7 39'7 49'5 4 9'2 66.4 3'8 7'7 16.2 24'4 36% 57'5 65 '4 90.1 No. z Artificial Blood Charcoal. - 8'7 18.1 27'9 43 'I 683 77'1 100.3 Dried at 120° C. Activated at 6ooo C. Activated at gooo C.Volume of 1 Volumeof 1 Volume of Oxygen in C.C. Oxygen in C.C. Oxygen in C.C. I I i 5 mins. 1 0 9 9 20 9 9 40 7 9 60 97 12 hours 2'0 3'6 5'7 8 2 9'7 20'6 49'0 79'0 188.0 203.1 204.3 206.4 213'6 148.5 Thc Acfivity of fhe Solid Impurities in fhe Active ChrcoaZ. In order to obtain some information as to the extent of the activity which might be attributable to the presence of the solid impurities, as such, present in the charcoals, the catalytic decomposition produced by the following sub- stances was determined :- I. The ash obtained by calcining a quantity of activated blood charcoal. 2. The ash from No. z artificial blood charcoal. 3. The ash from I after reduction by heating in a current of coal gas. 4. A sample of pu e reduced iron. 19 each case 0.25 gram of the substance was treated with 25 cc.of the The results are given in Table IV. hydrogen peroxide solution (= 245 C.C. oxygen). TABLE IV. Volume of Oxygen in C.C. Time. I I- 2'3 4'1 6.0 8.8 20'4 10'2 2 *I 3'6 5'8 8.3 9'6 21'2 1'4 2 '4 4'4 6-8 8'2 IS'SPEROXIDE SOLUTION BY BLOOD CHARCOAL 605 3 M 6 . Mins. 69.3 123.3 34.3 75.6 17'0 40'7 5.2 17-5 I t will be observed from the above results that the activity of thesesub- stances is relatively very slight. In Experiments 3 and 4 some of the iron is simultaneously converted to oxide. I t must not be overlooked, however, that the action of the isolated substance may be somewhat moddied when distributed throughout the mass of the charcoal. In Experiment I the bulk of the ash was 0.4 c.c., whereas the bulk of the charcoal containing this amount of ash was approximately 4 C.C.Decay in Aciivify of t h Charcoal. I t has been shown in previous papers (Zococ. cit.) and also in the present paper that the activity of charcoal in contact with hydrogen peroxide solu- tion rapidly falls off and finally disappears, even though a fair proportion of the hydrogen peroxide in solution remains undecomposed. The object of the following series of experiments was to determine whether the decay in activity was permanent or temporary. A quantity of finely divided charcoal was activated at 600' C., by Method III., previously de- scribed. The activity of the charcoal was then determined as in previous experiments. When the velocity of the reaction had become relatively slow ( i d . after about thirty minutes) the charcoal was filtered off and dried at 120' C.A quantity of the charcoal thus recovered was weighed out and the experiment repeated. The process was again repeated until the charcoal had been successively treated four times with hydrogen peroxide solution. The weights of charcoal used were 0.5, 0.4, 0.3 and 0.2 gram, and the volumes of hydrogen peroxide solution 5 0 c.c., 40 c.c., 30 c.c., and 2 0 C.C. respectively. The strength of the hydrogen peroxide solution was equivalent to 240% C.C. of available oxygen per 25 C.C. of solution. The results are given in Table V. and for the purpose of comparison the volumes are calculated for 0.25 gram of charcoal and 25 C.C. of the solution, in each case. TABLE V. 6 I2 24 Mins. Mins. Mins. M%. ------ 146'6 164'8 173'2 174'6 C.C.oxygen 118.9 142-7 161.3 1728 ,, ,, 60.8 96.0 153'0 167.5 ,, ,, 33'4 62-3 99.8 121-2 ,, ,, Time in Minutes. ! (I 0.5 I 6 IZ 24 Min. Mia. Mfns. Mins. Mins. Mins. ------- (I) 25 C.C. of solution 42.4 68.5 121.9 143.2 165.1 171.6 (2) Further 25 C.C. of solution added . 20'2 27.4 60'5 95.1 132'7 158'5 (3) Further 25 C.C. of solution added . - 4.9 16.1 30.2 61.4 92.3 First treatment Second ,, Third ,, Fourth ,, 30 Mins. 175.2 C.C. oxygen 160'2 ,, ,, 101.6 ,, ,, 0.5 Min. 41'2 2 1.6 The same problem was examined by a further series of experiments, in a different manner. When the velocity of reaction had become very slow, as in the previous experiments, instead of filtering off the charcoal, the con- centration of the solution was increased by the addition, from time to time, of further quantities of the original solution.TABLE VI.606 THE CATALYTIC DECOMPOSITION OF HYDROGEN (1) 443'6 (2) 221'8 (3) 110.9 (4) 55'5 ( 5 ) 27'8 (6) 13'9 0 - 2 5 gram of charcoal activated as before by Method 111. was treated with 25 C.C. of the hydrogen peroxide solution. 28'7 47'0 - 20.7 - 113 - 9'4 - 3'9 24'4 37'2 fizjuence of the Concentration of the SoZufion on the Activity of the Chrcoa 1. Charcoal activated by heating to 600' C. (Method I.), was treated with In all cases 0.25 gram of The results are given hydrogen peroxide solution of varying strengths. the charcoal was used, with 25 C.C. of the solution. in Table VII. Purified Charcoal ~ Dried at :zoo C. I TABLE VII. C.C. of Available of solution used. 1-1- 3 Mins.- 99'4 74'7 47'0 23.0 17'1 7'7 - 6 Mins. 154.8 1'4'7 68'4 33'7 21.9 11.4 12 Mins. $0 Mins. 339'7 170.4 101'4 51'6 - - C.C. oxygen evolved 9 9 9 9 9 9 ? I $ 9 9 9 9 ) 9 9 9 9 9 1 9 7 9 9 Temperature E'ecfs. The decomposition of hydrogen peroxide into water and oxygen is as- sociated with the liberation of approximately 23,000 calories per gram- molecule undergoing decomposition. Under the conditions of the experiments herein described, the influence of this heat liberated will be determined by the rate of decomposition of the hydrogen peroxide. When the velocity of the reaction is slow, the heat will be sufficiently rapidly dis- persed through the walls of the containing vessel to have very little influence on the temperature of the reaction. On the other hand, where the decom- position is very rapid, the temperature will rise appreciably.I t has already been shown in a previous paper (Cot. cit.) that the rate of decomposition of the hydrogen peroxide by charcoal rapidly increases with rise of tempera- ture, thus if the initial activity were sufficient to effect an appreciable rise in the temperature of the solution, then such a change would favour more rapid decomposition. The temperature effects were therefore approxi- mately determined for the various charcoals used. A simple glass calori- meter, consisting of a wide boiling tube fitted into a wide-necked flask, was TABLE VIII. Time in Minutes. I 3 6 24 30 60 I2 I 8.2 18-25 18.6 18-7 18.7 18.6 18-45 Temperature Readings. Activated by Method 1. I- - 21'2 24'3 26.2 25'5 23-6 22.7 18.4 Activated by Method 11.22'0 25.8 27.2 26.4 24'3 23 '35 18.5 Activated by Method 111. 22.9 27.1 28.7 27'4 25.0 23-85 18.6 Activated by Method IV. -I 24% 29'5 29'1 27-8 25 '3 24.2 I 8.8PEROXIDE SOLUTION BY BLOOD CHARCOAL 607 used. 25 C.C. of hydrogen peroxide containing 242.0 C.C. of available oxygen, were introduced into the boiling tube and 0.2 5 gram of the charcoal added. The initial temperature was 18” C. in each case and temperature readings were taken at intervals ranging from thirty seconds to ten minutes, according to the stage of the reaction. A summary of the results is given in Table VIII. Discussion of Resu Zts. The results given in Table I. show that blood charcoal, which has been dried at I 20’ C. is capable of bringing about the decomposition of hydrogen peroxide solution.In the case of charcoal not subjected to further purifica- tion, the rate of decomposition gradually diminishes until, after about fifty minutes, the rate becomes practically zero, whilst only about 25 per cent. of the hydrogen peroxide has undergone decomposition. In the case of the purified charcoals (Table I., 2, 3 and 4) although the initial activity is somewhat retarded, the rate of decomposition diminishes more gradually, the action being considerably prolonged. The reaction becomes very slow after two hours, whilst about 50 per cent. of the hydrogen peroxide has been decomposed. The effect therefore of the purification treatment ap- pears to have been to prolong the activity of the catalyst. From the typical results given in Table II., obtained after the charcoal has been activated, it is apparent that the activity of the charcoal is con- siderably increased by heating in a vacuum to 600’ C.and gooo C., and the activity is still further increased by previous sorption and removal of iodine. I t is important to notice that the effect of the various methods of activation is confined to the initial reaction. During the first thirty seconds, the percentage of hydrogen peroxide decomposed by the charcoals, activated by Methods I., II., 111. and IV. respectively, was 9-32, 9.68, 17.1 and 25-13, whilst after twelve minutes, the values are very similar in all cases. This is more clearly shown by a comparison of the velocity coefficients ; the values are widely different for the respective charcoals during the first six minutes, after which period they become very similar.In all four cases 74.5 per cent. of the hydrogen peroxide has been decom- posed in sixty minutes, after which period, the rate of decomposition has become relatively, very slow. The velocity coefficient has fallen after sixty minutes, to a value similar to the initial value for the unactivated charcoals. I t has already been pointed out (Rideal and Thomas Zoc. 02.) that the presence of iron in Fuller’s earth gives rise to a decomposition of hydrogen peroxide, in which the decomposition is ultimately almost complete and the velocity coefficient constant. In the present case, the decomposition is not complete within a reasonable period and the velocity coefficient con- tinuously diminishes over a very wide range.The fact that the iron con- tent of the purified charcoal and of No. 2 “Artificial Blood Charcoal ” is approximately the same as that of the Fuller’s earth, is interesting. I t should be noticed, however, that whilst in the case of Fuller’s earth the iron is present as oxide, in the case of blood charcoal the iron will, initially, be mainly metallic iron. The results given in Table III. show that the introduction of iron into pure sugar charcoal considerably increases the catalytic activity. In a previous paper (Zoc. a?.) it is shown that one gram of pure sugar carbon, activated by Method I., when treated with 25 C.C. of hydrogen peroxide solution, containing 336-8 C.C. of available oxygen, liberates 3-38 C.C. of oxygen in six minutes and 10.06 C.C.in thirty-three minutes, whereas similar charcoals containing added iron, to the extent of 1-46 and 9-10608 THE CATALYTIC DECOMPOSITION OF HYDROGEN per cent. ash, liberate 24.6 C.C. and 27.9 C.C. after six minutes, and 49.5 C.C. and 77.1 C.C. after thirty minutes using only 0-25 gram of the charcoal and hydrogen peroxide solution, containing 243-4 C.C. of available oxygen per 25 C.C. The results of experiment 3 (Table I.) and of charcoals activated by Methods I. and IV. are shown graphically in Fig. I by continuous lines 240 220 200 180 I 60 2 *: 140 c( 5 % P > 120 3 Io0 0 80 60 40 20 Fio. I. and are numbered I., 11. and 111. respectively, whilst the results for “artificial blood charcoal ” No. 2 activated by Methods I.and 11. are shown by broken lines and numbered IV. and V. respectively. The results given in Table V. show that the activity of the charcoal is considerably diminished by contact with hydrogen peroxide solution ; the activity is however partially recovered by drying at 120’ C. ; after four ex- periments it has become very small. Combining these results with those given in Table VI., it would appear that the extent of the decompositionPEROXIDE SOLUTION BY BLOOD CHARCOAL 609 is determined not only by the activity of the charcoal but by the concentra- tion of the solution. A concentration is ultimately reached at which the charcoal ceases to have any effect. From the experiments herein described, it does not appear that the extent of the decomposition is determined by the initiul activity, because from the results given in Table II., charcoals of widely different initial activities approach similar values after about thirty minutes.I t would ap- pear from the results, that the catalytic activity of the charcoal is of two types, one, a very rapid activity which decays after a few minutes, and a much slower activity which persists for a much longer period; both forms are capable of being increased. For convenience these two types of activity will be referred to as a and p activity respectively. Thus in the case of carbons not activated (Table I.) this a activity is absent. The slower /3 activity may persist for a comparatively short time or for a long period (Table I., I and 4). Hence from the data available, it is the /3 activity which determines the limit of decomposition for a given strength of solution: .provided the a activity is insufficient to bring about complete de- composition.The rate of decomposition is greatly influenced by the strength of the hydrogen peroxide solution as shown in Table VIL The extent of the decomposition will be determined by the rate of decay of the fl activity. With the weaker solutions the percentage decomposition is much greater than in the stronger solutions. Time of contact with the solution seems to be an important factor and if the rate of the decomposition is sufficiently rapid, the whole of the hydrogen peroxide may be decomposed before the charcoal becomes passive. In Table VL it is shown that in a solution in which the rate of de- composition has become very slow, if the concentration be increased by the addition of a further quantity of the original solution, the activity is increased.I t would appear therefore that the activity is determined by both the charcoal and the strength of the solution. A weakly active charcoal requires a strong solution of the peroxide for decomposition to take place whilst a more highly active charcoal is capable of decomposing weaker solutions. From Table VIII. it will be observed that during the initial stages of the reaction in which highly active charcoals are used, the temperature rapidly rises and since the rate of decomposition of the hydrogen peroxide increases with rise of temperature, this thermal effect tends to maintain a higher re- action velocity in the later stages than would occur if the temperature had remained constant throughout.The initial rate of the reaction is deter- mined by the u activity and this in turn, therefore, determines the thermal effects, so that the rate of reaction after the first few minutes is determined not only by the p activity of the charcoal but also by the thermal changes produced by the a activity. As the velocity of reaction diminishes the temperature gradually approaches the original temperature owing to loss of heat through the walls of the containing vessel. I t is important to note that if it were not for the initial rapid thermal changes, the demarcation between the a and /3 activity would be even more pronounced than is actually indicated by the results, i.c.the rise in temperature tends to counter- balance the decrease in activity of the charcoal. In considering the influence of the iron impurity present in the charcoal, it does not seem possible to explain the difference in the activity between sugar charcoal and blood charcoal on the iron content alone; a similar quantity of iron dispersed through Fuller’s earth has a very much lower activity and, also, the activity of the ash of the charcoal itself is very low.610 DECOMPOSITION OF HYDROGEN PEROXIDE SOLUTION It would appear, therefore, that the iron present in addition to increasing slightly the activity of the charcoal by virtue of its presence, greatly increases the activity of the carbon itself. It has previously been shown by one of us that the introduction of substances, either of a permanent or temporary character, into a carbohydrate prior to carbonisation, greatly increases the sorption activity of the resulting charcoal.I t is suggested that in the present case the original iron acts in a similar manner, that is, as a spacing agent whereby a less complex carbon molecule is produced than is the case when no such material is present. The results obtained for artificial blood charcoals, No. I and No. 2, show a wide difference in activity which cannot be solely accounted for by the difference of iron content alone and an ex- planation such as is given above seems reasonable. SUMMARY. I . Ordinary blood charcoal previously heated to 120' C., shows moderate catalytic activity in the decomposition of hydrogen peroxide soh tion. 2 . The catalytic activity of blood charcoal is considerably increased by previous heating in a vacuum at 600' C. and gooo C. and is still further increased by previous sorption of iodine from solution from which the iodine has been subsequently completely removed. 3. The activity of an activated charcoal consists of two types, one which is termed a activity which is very rapid, but ceases after a few minutes, and a second termed p activity which may persist for several hours. Both types may be increased by activation methods. I n ordinary blood charcoal a activity is absent. 4. The introduction of iron into sugar solution prior to carbonisation considerably increases the activity of the charcoal, by an amount greater than can be accounted for by the iron alone and it is suggested that the iron acts as a spacing agent thereby increasing the activity of the carbon itself. 5. The velocity of decomposition varies with the concentration of the hydrogen peroxide solution. 6. The proportion of hydrogen peroxide decomposed is determined by both the activity of the charcoal and the concentration of the hydrogen per- oxide solution. 7. In the case of the highly active carbons, the heat generated by the rapid decomposition of the hydrogen peroxide raises the temperature of the reaction, temporarily, by several degrees which further facilitates the de- composition of the hydrogen peroxide and thereby maintains the velocity of reaction at a higher level, until this heat has been dissipated. Firth, your. Sot. Chenz. I t ~ d . , 1923, G, 242T-244T. Chemistry Dejt., University CoZZege, Notti?Zghm.