HE OXIDATION OF PYRITES AS A FACTOR IN ‘THE SPONTANEOUS COMBUSTION OF COAL BY SHEO-HEN LI B.S., University of Illinois, 1922 M.S., University of Illinois, 1923 ABSTRACT OF A THESIS SUBMITTED IN PARTIAL FULLFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN CHEMISTRY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS, 1925 Reprinted from Industrial and Engineering Chemistry, Vol. 18, No. 12, page 1299. December, 1926. ACKNOWLEDGMENT This investigation was carried out under the direction of Professor S. W. Parr during the years 1923-1925 in the chemical laboratory of the Univer- sity of Illinois. The writer takes this opportunity to express his most sincere appreciation and thanks to Professor Parr for the valuable help and direction which he has given. The writer also wishes to thank Mr. F. B. Hobart for his suggestions and help in carrying out this investigation. REPRINTED FROM Published by the Ameriean Chemical Society Vol. 18, No. 12 Page 1299 December, 1926 The Oxidation of Pyrites as a Factor in the Spon- taneous Combus- tion of Coal’ By S. H. Li with S. W. Parr UNIVERSITY OF ILLINOIS, URBANA, ILL. Recent studies on the oxidation of coal seem to prove conclusively that oxidation proceeds very rapidly after a. temperature of 70° or 80° C. has been attained, and quickly reaches the autogenous stage, while at normal temperatures the oxidation is not ordinarily of suffi- cient magnitude to generate heat. The question there- fore arises as to the source and causes for an initial rise in temperature which is responsible for advancing the mass to the danger point. It is well known that coals that are very low in sulfur content are subject to this initial heating, and it is altogether probable that sulfur is not always the source of difficulty. Under certain conditions sulfur in the pyritic form may set up oxidation processes which may account for this initial heating. The present studies pro- ceed along the line of pyritic sulfur activity from the standpoint of fineness of division, form of crystallization, whether pyrite or marcasite, and the effect of bacterial and catalytic agents which might possibly be present in the original substance. The most pronounced indica- tion of oxidation was secured in the case of coals which started out with a high percentage of textural moisture which was allowed to be replaced by oxygen, and the most active condition at normal temperatures was secured with mixtures of certain types of clay. 1 Presented before the Division of Gas and Fuel Chemistry at the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, 1926. : (1) HE subject of spontaneous combustion of coal has been a topic of much discussion and experimentation. Owing to the complicated nature of the coal substance and the many factors that enter into the heat-producing reactions, no definite conclusion has been reached, especially with respect to the source of initial heating. Ample evidence is available to show that coal does heat in the presence of oxygen at elevated temperatures, say 80° C. or higher; yet this does not cover the fundamentals of the problem. It is unquestionable that coal piles will occasionally take fire in the absence of extraneous sources of heat and the question arises as to the initial causes for starting the heat increments. Presumably, the initial heat must be associated with the oxidation of either the carbonaceous materials or with the sulfur content of coal. Some coals with very low sulfur content may ignite, yet this does not mean that the pyrites is not a factor in other cases. Previous investigations?*? have shown that any form of pyrites, when finely ground, will absorb oxygen and enter into heat-producing reactions. Furthermore, owing to its low specific heat, pyrites will heat up faster than coal and it may act as booster for further oxidation activities. It is the primary purpose of this investigation to determine the role of pyrites in the initial heating of coal. Chief attention is given to the conditions which promote its oxidation at ordinary temperatures. Experimental Procedure The oxidation of mineral pyrites or the sulfur in. coal was determined by measuring the amount of increase of sulfate content before and after the oxidation. It was found from preliminary experiments that when a coal and pyrite mixture was oxidized in a stream of oxygen saturated with moisture the products of oxidation were retained in the mixture as sulfates regardless of the intermediate steps. There was no loss of sulfur due to volatile gases, although when the mineral pyrites was oxidized alone at 100° C. in the same way a small proportion of sulfur dioxide gas passed over. Thus the increase of sulfate content in coal-pyrite mixture is an accu- rate measure of the degree of oxidation of the pyrites. The oxidation of pyrite-coal mixture was carried out in an apparatus devised by Prof. J. White,* of Rose Polytechnic Institute. The principle and operation are self-explanatory from the sketch as shown in Figure 1. Its essential feature is a double-walled tube with ends closed with corks. The space between the two tubes is filled with water vapor gener- ated from a flask on a hot plate. The upper part of the ap- paratus is provided with a return condenser. The con- densed water returns to the flask through a by-pass. 2 Winmill, Trans. Inst. Min. Eng. (London), 51, 500 (1916). 3 Graham, Jbid., 6%, Pt. 2, 100 (1924). 4 J, Franklin Inst., 178, 201 (1911). (2) In this apparatus the substance to be oxidized can be kept at any desired temperature for a long period of time by using different liquid heating media. Oxidation was carried out at two different temperatures, one at 100° C., using water as a heating medium, and the other at room tempera- ture, which varied from 23° to 27° C., designated as 25° C. At room temperature a single glass tube was used instead of the double-walled heating apparatus, other arrangements being the same. 3 | oxygen —_—> Figure 1 Samples of 5 grams each of coal or coal-pyrite mixture, accurately weighed out, were put in small aluminum boats and placed in the inner tube. Oxygen, saturated with mois- ture by bubbling through a wash bottle containing distilled water, was passed over the coal and discharged into the atmosphere, since the oxidation of the coal substance is dis- regarded. The wash bottle containing distilled water, in the case at 100 ° C., was placed near the hot plate to keep it fairly warm and thus enable the oxygen to carry plenty of moisture when it enters the apparatus. After a certain time of oxidation duplicate samples of 5 grams each were transferred to large beakers and their sulfate content de- termined. The percentage was calculated on the basis of total sulfur, deducting the sulfate originally present. (3) The method used for the determination of sulfate was that worked out by Powell and Parr.® The method consists of extracting the coal with 3 per cent hydrochloric acid at 60° C. for 40 hours. After filtration the sulfate is deter- mined as usual. Duplicate samples were run in all the cases and a good check, variable within 0.01 per cent, was fre- quently obtained. Oxidation of Sulfur Originally Present in Coal Four samples of Illinois coal from four counties in Illinois— (1) Jackson, (2) Randolph, (3) Franklin, and (4) Vermilion— were examined with regard to their sulfur content and rate of oxidation. The coals were in each case ground to pass through an 80-mesh sieve and oxidized in a stream of satu- rated oxygen as described in the experimental procedure. The first two—from Jackson and Randolph counties—were air-dried while the other two retained their textural moisture. Oxidized a Per Cent of Su/ohur Stim e ve peers Figure 2—Oxidation of Sulfur in Illinois Coals at 25° C. in Oxygen Saturated with Moisture The results as represented in Figures 2 and 3 show that (1) the rate of oxidation of sulfur in air-dry coal varies with the temperature; (2) coals with high initial moisture may have a high rate of oxidation of sulfur at normal temperatures. From these results it seems desirable to study the factors which influence the rate of oxidation. The difference in the rate of oxidation of the sulfur in coal may be due to several causes, as (1) the presence of certain readily oxidizable forms of pyrite in some of the samples (to be discussed in a later paragraph); (2) the initial textural moisture content in the samples; and (3) some samples con- tain more of the very finely divided pyrites. To prove the | last point a sizing test was made by sieving the samples 5 University of Illinois, Eng. Exp. Sta., Bull. 111 (1919). (4) 4 = through screens of different sizes with sulfur content de- termined on each portion. The results of this test, together with related factors, are given in Tables I and II. Table I—Distribution of Total Sulfur with Reference to Fineness of Division Through 80 Through 140 ‘Through 200 325 mesh to on 140 mesh on 200 mesh on 325 mesh dust size Per cent Per cent Per cent Per cent Vermilion 5.09 24.20 26.86 43.85 Franklin 12.59 25.09 32.85 29.47 Jackson 9.49 19.55 21.80 49.16 Randolph 8.44 20k 26.10 36.15 Table II—Proximate Analysis of Samples of Illinois Coal, with Special Reference to Their Sulfur Content and Its Distribution in Various Forms (Organic sulfur equals the total sulfur minus sulfate sulfur plus pyritic sulfur) Vermilion Franklin Jackson Randolph Per cent “Per cent Per cent Per cent Moisture 10.54 6.95 1.67 3.87 Ash 12.26 5.05 8.66 13.43 Total sulfur 3.748 1.384 Seivs 2.590 Sulfate sulfur 0.071 0.022 0.132 0.012 Pyritic sulfur 1.914 0.412 3.165 0.596 Organic sulfur 1.763 0.950 1.876 1.982 Total oxidizable sulfur 3.677 1.362 5.041 wpagay ts r Oxidized v pedi ere bale aly Fane aa fepeme lm ale ala] | Per Cent of Sulphy yay oa SV aaa eee ws cod a ci VAS ic oa aed etd Ds i ER ae in Weeks Figure 3—Oxidation of Sulfur in Illinois Coals at 100° C. in Oxygen Saturated with Moisture The fineness factor enables us to explain the behavior of sulfur only ina general way. Vermilion and Jackson County coals have a high percentage of sulfur in the fine sizes, yet the latter did not show nearly so high a rate of oxidation as the former. The difference may be explained by the fact that Jackson County coal contains a considerable amount of sulfate sulfur which probably is very finely divided, leaving the actual oxidizable sulfur in the coarser portions. (5) The sulfur in Jackson and Vermilion County coals have about equal rates of oxidation at 100° C.; yet the latter is considered much more in danger of combustion in storage than the former. The Vermilion coal contains a high per- centage of sulfur, which, most important of all, has a high rate of oxidation at ordinary temperatures. Vermilion coal also seems to-be more fragile than the other samples examined. This would increase its danger of firing in storage. Pyrite — Marcasite Figure 4—Pyrite and Marcasite Used in This Investigation Oxidation of Pyrite and Marcasite It is often suggested in the literature that the marcasitic form of iron sulfide is much more readily oxidized than the pyritic, yet there is no experimental evidence as to what extent this is true. Graham,' in his study on the absorption of oxygen by different forms of pyrite, found that marcasite did not have nearly so high a rate as one sample of massive pyrites. He interprets his result as due to size. He said that ‘‘the difference observed between marcasite and the Cornwell pyrite may possibly be due to size, since micro- scopic examination of the two powders rather indicated that the latter, when crushed to pass through a 200-mesh sieve, formed finer particles than the former.” (6) In view of this uncertainty it seemed advisable to carry out more work along this line. One sample of cubic pyrite and one of marcasite were examined for this purpose (Figure 4). The sample of pyrite, obtained from Leadville, Colo., came in as perfect cubes with bright, brassy surfaces evi- dently untouched by oxidation. The marcasite was ob- tained from the geology department of the University of Illinois, its source being unknown. The marcasite had a needle-like crystalline structure with dull grayish tin color, and showed slight oxidation on the surface. The minerals were identified by Penfield’s method® of distinction and shown to be correctly designated. The minerals were pulver- ized to the same degree of fineness and mixed in the propor- tion of 3 per cent of minerals with Randolph County coal and oxidized with saturated oxygen at two different tempera- tures—100° and 25° C. The difference between the sulfate content of the coal-pyrites mixture and that of the Randolph County coal when oxidized alone gives the rate of oxidation of the minerals. The results are graphically represented in Figures 5 and 6. Marcasite has a slightly higher rate of oxidation at 25° C., while at 100° C. the reverse is true for the sample ground to pass 325 mesh. This may be due to the fact that the in- crease of temperature has a slightly greater effect on the oxidation of pyrite than of marcasite. For the samples ground to pass through 140- and caught on 200-mesh sieve, the two curves are in general agreement when they were oxidized at 100° C., the pyrite having slightly higher rate for the first part of the experiment, while later the condition is reversed. This slightly higher rate of oxidation of marcasite at 25° C. does not necessarily indicate that it is more readily oxidized than pyrite. It is believed to be due more to its highly fragile nature, and to more fine material being produced during grinding. In samples of pyrite and marcasite ground to pass through a.200-mesh sieve, it was found that the iatter contains a higher proportion of the finer particles; 92 per cent of marcasite passed through a 325-mesh sieve com- pared with 71 per cent of the pyrite. This ratio is probably also true in that proportion which passes through the 325- mesh sieve. Factor of Fineness of Division The effect of fineness of division was studied by separating the same sample of pyrite used in the previous experiment into four portions, mixing with Randolph County coal, and oxidizing each in saturated oxygen. From an examination of the results (Figure 7) several features are noticeable. The rate of oxidation seems to be a function of the size of particles, the oxidation of pyrite being nearly a linear function of its surface area. 6 Brush and Penfield, ‘‘Descriptive Mineralogy,” 15th ed., 1898, p. 252. (7) We may assume that the surface areas of two powders of certain unit volume are in inverse ratio to the average diam- eter of their grains, as suggested by Purdy,’ if we assume first that the distribution of each portion is graded uniformly. It will be noted that the ratio of the reciprocal of the average diameters of the different portion and that of the percentage oxidation of the pyrite for 6 weeks are quite close. The relationship between the rate of oxidation, temperature, and the size of the particle can be expressed mathematically as follows: te R D K where R = rate of oxidation of pyrites T = temperature in ° C. D = diameter of the particles K =a constant; depends upon form of pyrite considered — This equation indicates in a general way that the rate of oxi- dation is directly proportional to the temperature and in- versely proportional to the diameter of the particles. Probable Catalytic Oxidation We have learned from the above experiments the nature or behavior of the pyrites alone when present in coal. How- ever, the presence of certain substances or. catalytic agents might affect the rate of oxidation of pyrite to a great extent. The following substances have been studied for their possible . catalytic action on the oxidation of pyrites by mixing them with Jackson County coal and oxidizing the mixture in saturated oxygen at room temperature: (1) Indiana clay, found underneath the kaolin deposit in Lawrence County, Indiana; (2) Tennessee ball clay; (3) coal highly saturated with oxygen; (4) sulfur oxidizing bacteria; (5) carbonated calcite water and common salt; and (6) mother of coal. The first three substances showed considerable catalytic action while the last three gave negative results. A word might be said about the Indiana clay. Logan® has described some experiments with black clay which was found underneath the kaolin deposit in Lawrence County, Indiana. This clay was shown to contain sulfur bacteria of some species closely related to that of the genus Beggiatoa. ‘To this type of organism was ascribed the mineral alteration from feldspar to pure kaolin. Some of this clay was obtained from the Gardner mine in order to test its possible action toward pyrites. The clay as received was yellowish rather than black, had fine texture, some plasticity, and granular structure. ; The so-called sulfur-oxidizing bacteria were a pure culture, Thiobacillis thio-oxidans, obtained from Dr. Waksman of the New Jersey Agricultural Experiment Station. The bacteria culture was kept in a liquid mixture® containing some sulfates 1 Trans. Am. Ceram. Soc., 7, Pt. III, 441 (1905). See also Cushman and Hubbard, J. Am. Chem. Soc., 29, 589 (1907). 8 Dept. of Conservation, State of Indiana, Publication 6, (1919). ® Waksman and Joffe, Soil Sci., 12, 475 (1922). (8) and elementary sulfur. This culture was supposed to oxi- dize mainly elementary sulfur. Thus so long as the mixture contains any elementary sulfur, it would have no effect upon the oxidation of pyrite. The curves in Figure 8 show the result of this series of tests. Indiana clay has the greatest effect among the substances studied. In the presence of this clay the rate of oxidation of the sulfur in coal was about doubled. The catalytic action of Indiana clay was also tried on Vermilion County coal. The part of the total sulfur in this coal oxidized in 1 week was 4.19 per cent and 8.15 per cent in 2 weeks, while in the presence of the clay they were increased to 8.06 and 12.53 per cent, respectively. The latter rate is practically equal to that at 100° C. i een a arcusife al\/00% Per Cent of Sulphur Oxidized | pars Bes ree isto: -sipid in nie BEE Figure 5—Comparison of Rate of Oxidation of Pyrite and Marcasite at 100° and 25° C. in Oxygen Saturated with Moisture, Both Minerals Passed through 325-Mesh Sieve Effect of Moisture and Oxygen Concentration In the previous experiments pure oxygen was used for oxidation for the purpose of hastening the reaction and thus reducing the time of the laboratory processes. Some experi- ments seem to be necessary to show the significance of con- centration of oxygen and its mode of action, as well as that of moisture in the coal. Six series of experiments were carried out in this direction on Vermilion County coal. The main features of the work may be outlined as follows: (9) (a) Coal containing high textural moisture was oxidized with oxygen saturated with moisture. (6) Coal containing high textural moisture was oxidized with air saturated with moisture. (c) Coal containing high textural moisture was oxidized with laboratory air unsaturated with moisture. (d) Coal was dried in the laboratory air until its moisture equilibrium was established and then oxidized with oxygen saturated with moisture. (e) Coal was dried as in (d) but was again sprinkled with water on the surface by means of an atomizer and then oxidized with oxygen saturated with moisture. (f) Coal containing its original textural moisture was sub- jected to slight pressure (about 15 inches of water) under oxygen for one week with the idea of letting the coal absorb as much oxygen as possible. Then the samples were stoppered in bottles and set aside. After each week determination of sulfate content was made on duplicate samples. The results of this series of tests are represented in Figure 9. It will be noted that when air is used instead of oxygen 3 a | o > fs Per Cent of Sulohur Oxidized o Time in Weeks Figure 6—Comparison of Rate of Oxidation of Pyrite and “Marcasite at 100° and 25° C. in Oxygen Saturated with Moisture, Both Minerals Passed through 140-Mesh and Caught on 80-Mesh Sieve the rate of oxidation is reduced to about half of that for corresponding values with oxygen. In series (c), where the air was not saturated with moisture, the.amount of which depends on the relative humidity being fairly low in the laboratory atmosphere, the oxidation of pyrite was slow or practically negligible after the first week. The sulfate formed during the first week was derived from the moisture originally present in the coal. Series (d), (e), and (a) demonstrate clearly the effect of the moisture content of the coal on its textural condition. The removal of initial moisture from the coal decreases the rate of oxidation of sulfur, especially at the first stage. As the oxidation goes on, when enough moisture is absorbed into the coal the normal rate gradually recovers. Rewetting after drying does not restore the original speed quickly, the difference being probably due to uneven distribution of the moisture. After several weeks the moisture is more uniformly (10) distributed, and the oxidation goes on with its original rapidity or the rate may even be higher. In series (f) we provide another set of conditions for the oxidation of the sulfur. All the initial moisture is retained, plenty of oxygen is absorbed into the coal mass, and in addi- tion there are a few cubic centimeters of oxygen above the surface of the coal in the bottle. Everything that is neces- sary for the oxidation is present in a confined space; yet the oxidation goes on with extreme slowness. During the week when the samples were under oxygen pressure, there was only 2.39 per cent of sulfur oxidized as compared with 4.19 per cent when it was oxidized in a moving stream of saturated oxygen at the same temperature. Therefore, the best con- dition for the pyrites to oxidize is in a moving stream of oxygen saturated with moisture. High moisture in coal seems always to be accompanied by rapid oxidation of the pyrites in the coal. As the moisture in the coal evaporates oxygen moves in to fill its place. The oxygen in this stage behaves in a way similar to oxygen in the nascent state, and appears to be much more active than the ordinary form of the gas. Discussion of Results As indicated at the beginning of this paper, the present study aims primarily to determine the ,oxidation behavior of pyrites at normal temperatures. There is ample evidence to show that at higher temperatures—say 75° C.—oxidation becomes so active as to proceed rapidly to the autogenous stage. The real question involved, therefore, is—how does coal reach those temperatures above the normal in coal piles aside from external sources such as hot walls, hot pipes, ete., which may bring the mass up to the danger point? The studies here given are directly concerned with the role that pyritic sulfur may play in this direction. It has been demonstrated that pyrites will oxidize when oxygen and moisture are present. The oxidation is quite rapid under suitable conditions and enough heat may be liberated to raise the coal to the danger point. The heat production of the oxidation of pyrites has been studied by Parr and Kressman,!° Winmill,? and Graham.’ The reaction may generally be represented by the following equation: 2FeS, + 702 + 2H2O0 = 2FeSO, + 2H2SO. + heat The further formation of ferric sulfate is generally believed improbable due to the reducing action of the carbonaceous materials present in the coal. Parr and Kressman calcu- lated the heat produced indirectly from the heat of com- bustion of pyrites into ferric oxide and sulfur dioxide as. determined by Sommermeier. They found that for every two molecules of pyrites oxidized there are 624 large calories of heat liberated, not taking into account the heat of solution 10 University of Illinois, Eng. Exp. Sta., Bull. 46 (1910). (11) of sulfuric acid or of the hydration of ferrous sulfate. This when figured to volume of oxygen absorbed is equivalent to 4.1 calories for every cubic centimeter of oxygen absrobed. This calculation was confirmed by Winmill, who found by actual determination, 4.3 calories evolved for every cubic centimeter of oxygen absorbed. Let us now take one instance from this investigation and figure out its thermal effect, approximately as nearly as pos- sible the actual conditions on the coal piles. Vermilion County coal contains 3.75 per cent of sulfur and we may assume an oxidized condition of about 20 per cent. Suppose Per Cent of Sulphur Oxidized AY | mi ae D [ a a a ey: ae ui ge TU on |_| 325) cab hog == 80) on 4 Figure 7—Oxidation of Pyrite at 100° and 25° C. in Oxygen Saturated with Moisture that the coal pile contains a layer of fines which in turn contains about 50 per cent of finer stuff of the same degree of fineness as the samples used for the experiments. ‘The dilution would probably decrease the heat effect on the temperature of the coal also about 50 per cent. Take 1 kg. of the coal into consideration; this amount of coal contains 37.5 grams of sulfur. At the end of 6 weeks 20 per cent, or .75 grams, of it is oxidized. This amount of oxidation will evolve 37.6 large calories of heat. The specific heat of coal was first roughly determined by Trefall and more recently (12) by Coles. It was found to vary with the moisture content and theC: Hratio. In general it lies between 0.2 to 0.4, and the average value of 0.3 may be taken for illustration here. The amount of heat as obtained above will raise 1 kg. of coal 37.6 (Sn x 0. 5) 125.3°C. Allowing 50 per cent due to the dilu- tion by the coarser particles, which is assumed to be inert, we have a rise of 62.6°C. This will raise the temperature of the coal pile from 25° C. to above 85° C., which is well on the way to the danger point. This illustration is based on the natural rate of oxidation, independent of any of the catalytic agents. Should there be some catalytic agent present, such as Indiana clay, the rate can be at least doubled and vigorous heating is sure to occur. Furthermore, this estimation is based on the rate of oxida- tion at 25° C., but in effect the rate is always increasing a = hur Ox1d (zed ie eae Be omy fie el a a bala ii Ate /P \ SN eae i) Reet Ht+-HHe ~ Per Cenk of Suf ieay GRaNNGaS fo REN S@i ae SONG er AN ees ZT aoe ahah Time in AE Figure 8—Oxidation of Sulfurin Jackson County Coal at 25 °C in Presence of Various Catalytic Agents LG ° -~ gradually due to the augmentation of heat given out from the reaction, if it is not dissipated. If we take this into consideration, the estimation would be too low. ‘The accel- erating effect of increased temperature might more than offset radiation losses. Coals may also contain a pocket or lens of pyrites in a finely divided condition. This would certainly make a hot spot in the coal pile and its ignition action would be probable. Of course the behavior of pyrites in coals differs widely, as shown by the first part of this investigation. Some oxidize very rapidly and others are much more inert. Some coals have low sulfur content and the rate of oxidation of the (13) latter may also be slow. In such a case the self-heating, should it happen in the coal, must be traced to the oxidation of carbonaceous material. On the other hand, in high- sulfur coal the pyrites may be a contributing cause for heat generation. In certain cases, indeed, pyrites may be the chief cause while in other cases the carbonaceous material may be active. Should they both be operative in the same coal they may each contribute to the final heating. Pre- vious reports may sometimes have been mistaken in stating that pyrites could not be the cause of spontaneous combus- tion of coal because some coals had ignited with very low sulfur content; others which say that the heat resulting from the oxidation of pyrites is not enough to raise the tem- (ay led aa ae we ee fy Z| nb eat sohe oA Johure fee Ka Per Cent of Sulphur Oxidized BS by oi EEE: El = ECON Ss mm > oN ~ ~ Uy ny iW, ie E LH) s2ep sen) A eee o S Ti cP in Weeks Figure 9—Oxidation of Sulfur in Vermilion County Coal at 25° C. with Varying Conditions of Oxygen and Moisture perature of the coal to ignition may also be in error. Coal is a very complicated substance and its characteristics vary widely according to its origin and types. Many factors enter into the heating of coal; each may contribute a certain part and codperate with the others in the development of initial heat. Summary and Conclusions 1—Under suitable conditions the pyrites in coal a oxidize rapidly and may be a dominating factor in certain cases for the self-heating of coal. (14) 2—Marcasite and pyrite oxidize with about the same rate, but the former breaks down more easily producing fine particles, thus facilitating its oxidation. 3—The rate of oxidation of pyrite or marcasite is directly proportional to temperature and inversely proportional to the diameter of the particles. | ? 4—Dry air or oxygen does not promote the oxidation of the pyrites. 5—High textural moisture seems to be accompanied by rapid oxidation of the pyrites. A moving stream of oxygen saturated with moisture seems also to be the best accompani- ment for the oxidation of pyrites in the presence of high textural moisture. The fact that high textural moisture promotes oxidation of pyrite is presumably due to the evapo- ration of the moisture and its subsequent replacement by oxygen. The oxygen in this state appears to be much more active than under ordinary conditions. ‘There may be a catalyzing effect set up by this interchange of moisture and oxygen or a possible activation of the coal surfaces which results in a greater activity being imparted to the oxygen. 6—The catalytic oxidation of certain substances such as Indiana clay is presumably due to the presence of a certain type of bacteria in the clay. That the catalytic action is not from the colloidal nature of the clay alone seems evident from a comparison of the experiment with ball clay, which probably contains more of the colloidal material, yet does not produce so much catalytic action. (15) cd Wate’ The writer of this thesis was born in Vhing, Kiangsu, China, February 1, 1898. Following his primary school training, he entered the Fifth Provincial Middle School at Chang Chow, Kiangsu, China, and graduated after a four years course in 1917. He entered the University of. Nanking, at Nanking, China, in the fall of 1917, registering in the College of Agriculture. After three years at Nanking, he came to the United States and entered the University of Michigan, registering in the course of chemical engineering. He was at Michigan for one semester and then transferred to the Uni- versity of Illinois, and graduated from the course in chemical engineering in 1922. In the fall of 1922 he took up graduate work in the department of Chemistry of the University of Illinois and has continued in the work until the present time. He received. the degree of M. 8S. in Chemistry in 1923. While in attendance at the University of Illinois he has held the position of Graduate Research As- sistant in Chemical Engineering from 19238 to date. 3 0112 073236934 coe ‘ :