October 20, 1916. THE COLLIERY GUARDIAN. 763 of the powder was completely oxidised, whilst the remainder still retained the brassy lustre. The pyrites therefore seemed to be mixed, so far as its resistance to the oxidising action of the air was concerned. The apparatus in which the oxidation was carried out was of the form of a large horizontal condenser, and con- sisted of a glass tube (140 X 3’75 cm.), surrounded by an iron tube (125 x 5 cm.) as jacket. Steam was passed through the annular space between the two tubes. Fifty grammes of the material for oxidation were placed in the spaces between five wet glass wool plugs, which were introduced to keep the air moist during its passage through the inner tube. The air was drawn through the tube by means of a filter pump at the rate of about 1| litres per hour, and was freed from carbon dioxide and sulphur dioxide before entering. On leaving the inner tube, the air bubbled through three absorption bulbs containing potassium hydroxide, in which the carbon dioxide and sulphur dioxide resulting from the oxidation of the material in the tube were collected. During the experiments, each of which occupied 36 hours, steam was blown through the iron jacket, with the result that the temperature of the air leaving the inner tube varied from 36 to 39degs., having entered at 15 to 18degs. At the close of each experiment the contents of the tube and the absorption bulbs were tested for oxidised products. The results were corrected for the “ blank ” estimations which were made in all possible cases. In experiments (1) to (3) the oxidised iron and sulphur in the residue in the tube were extracted with air-free, dilute hydrochloric acid, whilst in experiments (4) to (5b) the amount of iron oxidised to the ferric state was estimated volumetrically, and is given as a percentage of* the total iron present. The results, calculated for the specified weights of the substances, are tabulated below :— a). (2). Substances . » for oxidation. » S g 6D ho O § s (3). (4). (5a). (5b). (6). Grm. Perc. Perc. Perc. C.c. 0’5240. ..82’39. ..79’68. ..52’79... — £ O P to rA -5 ft 2 A he co cc a O O 6Wo . 2o a^ °o OpA 02 o o A A CD pl A K eg O eg o 5 A A A l—1 A <~| .. 0’3225... — ... — ... — ... — .0’2786 — ... — ... — ... — ...0 6011... — ... — ... — ... — C.c. C.c. C.c. Gim. C.c. Iron oxidised 0*6)10... — Sulphur oxi- dised to SO4 0’5730 .. — Sulphur oxi- dised to SO2 0T405... — Total sulphur oxidised ... 0’7135... — Carbon di- oxide......... - .. 24T7... 82’8 ... — ... 8 17...45’6 ... 18’8 Discussion of the Results. (1) In this experiment it would be expected that if 0-7135 grm. of sulphur of the iron pyrites were oxidised, 0-6243 grm. of iron would become soluble in the acid. The amount actually determined was higher. This may be due to the pyrites becoming more finely divided, so that a larger quantity of the excess of iron (1’02 per cent.) in the pyrites would be available to the action of the acid than in the blank determination on the ordinary sample. An analysis of the solution extracted with the air- free, dilute hydrochloric acid from the pyrites left in the tube indicated the presence of almost pure ferric sul- phate. From this it may be concluded that under the conditions of the experiment, and in the absence of carbonaceous matter, the pyrites oxidises to form ferric sulphate. (2) *No oxidation of the iron and sulphur, which occur naturally in the coal in small quantities, could be detected. (2 and 3) The analysis of the solution extracted in experiment (3) indicated that the oxidation of pyrites under the conditions of the experiment, and in the pre- sence of carbonaceous matter is mainly to give ferrous sulphate. The most notable point was the increase in the evolu- tion of carbon dioxide from 24’17 to 82-8 c.c. This seemed peculiar, for some investigators state that there is no liberation of oxidised gaseous products from coal until the temperature reaches lOOdegs. or above. It may be noted that the portion of the coal in contact with the tube might have its temperature raised to this value, although the temperature of the air passed over it never exceeded 39 degs. Another point is that in the experiment with the pyrites alone, more of this mineral was oxidised than when it was mixed with coal. This may be due to two factors : First, the coal may have exercised a deterrent effect by absorbing the oxygen; secondly, the ventila- tion of the mixture may not have been so effective, for the volume of 50 grms. of the mixture exceeded the volume of the same weight of powdered pyrites. (4 and 5) These experiments were conducted in order to determine whether the iron compounds produced by the oxidation of the pyrites caused an increase in the volume of carbon dioxide liberated. In experiment (5a) a small volume was obtained, but this was probably due to the fact that, after a few hours, the coal was saturated, and was finally submerged. The experiment was repeated (5b) with a mixture containing 5 per cent, of ferrous sulphate, and from this mixture the volume of carbon dioxide collected rose to 45’6 c.c., whilst the per- centage of iron oxidised to the ferric state only reached 52-79. Again, in this experiment the coal appeared moist after about 29 hours, but the result seems suffi- cient to show that the ferrous sulphate increases the liberation of carbon dioxide by the coal. (6) The results indicate that any sulphuric acid pro- duced by the oxidation of the pyrites would not aid in the production of carbon dioxide. The volume of carbon dioxide liberated in this case was far below that obtained from the coal alone. This may be due to the dilute sulphuric acid filling the pores, and thus preventing the oxygen of the air from penetrating the coal dust. Iron Pyrites and Oxygen Absorption. Experiments were conducted to determine how the admixture of iron pyrites, ferrous sulphate, and sulphuric acid with the coal influenced its absorption of oxygen. Six large flasks of almost equal volume were clamped horizontally, and fitted with rubber stoppers, through which passed glass tubes 120 cm. long. These were bent at right angles 10 cm. from the flask, and their ends dipped under water, so that the absorption of oxygen could be measured by the rise of the water up these tubes. Had the absorption proved large, the ends could be immersed in mercury so that the flasks should not be flooded with water. The absorption of oxygen by the sample of “ King ” coal, however, was exceptionally small; incidentally, this may account for the fact that no case of spontaneous ignition has occurred in this seam. Into five of the flasks were placed 50 grms. of the following powders : “ King ” coal, iron pyrites, a mix- ture of equal weights of iron pyrites and coal, ferrous sulphate, and a mixture of coal with 5 per cent, of ferrous sulphate, whilst the sixth flask contained a mix- ture of 50 grms. of coal with 5 c.c. of dilute sulphuric acid (1 in 10). The sample of coal was mined in the morning, and brought to the laboratory early in the afternoon. Four large pieces of coal (about 22’5 cm. cube) were broken, open, and the central portions of about 70 grms. were taken from each. This coal was rapidly powdered, sieved, mixed as stated above, and placed in the flasks. An analysis of the sample is given below :— Ultimate Analysis. Per cent. Carbon ........................... 81-069 Hydrogen .......................... 5-666 Nitrogen .......................... 1-088 Sulphur ........................... 1-042 Ash ............................... 3-338 Oxygen, etc. (by difference) ...... 7-797 100-000 Proximate Analysis. Per cent. Coke ............................. 62-085 Ash ................................ 3-338 Moisture ........................... 2-269 Specific gravity of the coal = 1-291. A wide boat containing freshly-slaked lime was placed in each flask to absorb any carbon dioxide which might be evolved, and to keep the air moist a wet glass wool pad was introduced into each of the necks of the flasks. At the close of the experiments a test made for methane showed it to be entirely absent. The volume of air in each of the flasks was deter- mined. Readings of the atmospheric pressure, temper- ature (which varied from 13*2 to 15-8 degs.), and the level of the water in the tubes were taken every three hours during the daytime for seven days. From these readings the volumes of oxygen absorbed by the specified weights of material were calculated, and are recorded in cubic centimetres in the table below. (a) (M co