through the water, and that the loss of heat on this account is not unimportant. I have not as yet given much thought to this form of calorimeter; but it would seem an easy thing to overcome, by some simple mechanical device, the fault which Dr. Percy has pointed out, and thus secure a useful, though not a precise instrument. A more practical method among those of a less refined and delicate nature is that of Berthier. This depends upon the fact that carbon, when heated in the presence of litharge, reduces the litharge in accordance with the following reaction,— 2 PbO + C = CO2+2Pb 25 34.5 and, calculating from the known atomic weights of carbon and lead, we find that for every gram of carbon present, thirty-four and fivetenths (34.5) grams of lead will be obtained. Berthier proposed to perform the experiment by heating the coal, in a finely-divided state, in a crucible, with about forty times its weight of litharge, and continuing the process at a red heat, for some time. The crucible was then allowed to cool; it was then broken, the button of lead extracted, washed, dried, and weighed, and on the above equation the weight of carbon calculated. Suppose we find that a given sample yields 25 grams of lead; then the heating power is of that of pure carbon, or assuming that 1 kilogram of carbon raises 7,900 kilograms of water 1° C., 1 kilogram of the sample of coal is capable of raising 5,724 kilograms of water 1°C. To estimate the evaporative power by this method. we have simply to divide the number of units of heat obtained by 537, the units of heat necessary to vaporize 1 kilogram of water at 100° C, Many objections to this process have been raised, but it seems to me as unobjectionable as any that have been devised. Among other objections it is urged that hydrogen may be present in the coal to a greater extent than the oxygen necessary to combine with it to form water, and that this free hydrogen, if we may so term it, will reduce a part of the lead, and that by assigning the whole to the carbon very serious errors. may be introduced. On the other hand, it may be said that according to the reaction, PbO + 2H H2O + Pb one part of hydrogen will reduce 103.5 parts of lead, while one part of carbon reduces 34.5 parts of lead, or 3:1; but at the same time the units of heat produced by the hydrogen are to those produced by an equal weight of carbon as 4.265: 1. Now, as the hydrogen is in the solid condition, some heat will be absorbed in converting it into a gaseous form: therefore, in valuing the coal for purchase, when this error exists The it will be in the right direction. In using the method, however, I have found a source of error which has led me to modify the details of it. When a crucible is used it is placed in a furnace where it is difficult to manage, and there is great danger of the reducing gases of the furnace reaching the litharge. Hence, instead of the crucible I employ an iron tube, or gas pipe. Into a piece of gas pipe (ungalvanized) one inch in diameter and one foot long, a plug, tightly fitting, is screwed at one end, and a second piece of pipe, one half inch in diameter and three feet long, is screwed at the other. One gram of the coal to be examined, finely powdered, is now mixed with about forty times its weight of litharge, and poured into the tube and covered with a small quantity of litharge. The tube is then placed in the furnace under a boiler, the open end extending out six inches, and allowed to remain there until upon placing the finger over the open end no pressure is felt. process does not occupy over ten minutes. The tube is then removed, the closed end rapped sharply on the hearth to cause all the molten lead to descend, and it is then placed in a vise. In the mean time a small box is lined with plaster of Paris for the reception of the lead. This is placed under the tube and the plug is removed and the lead allowed to run into the box. During this operation the tube is rapped with a hammer to facilitate the escape of the molten lead. After the tube is cooled it is frequently found that some of the metallic lead has been caught in the thread, but it is easily got out. Care must, however, be taken not to mistake fused litharge for metallic lead. The lead which is now collected is washed, dried, and weighed, and the calculation made as above. It is found that after a tube has been used two or three times it gives more constant results than at first. The following determinations, made in this laboratory, prove that this process gives closely agreeing results. One gram of coal was taken for each experiment. All but the last four of these analyses were made by Lt. Charles Belknap, U. S. N., Instructor in Physics and Chemistry. The last four were made by Cadet Eng. A. T. Woods, U. S. N. In order that the process should give reliable results, it is essential that the litharge should be pure. If, as was the case with Johnson's experiments, the litharge contains minium the results will be too low. As some experimenters have found it difficult to obtain constant results with litharge, Mitchell has proposed the use of the ordinary carbonate of lead, but I am disposed to believe that this would be an unwise change, as the composition of the carbonate exhibits greater variations than that of the litharge. It has been said of Berthier's process that in the Admiralty investigation the results exhibit a variation often amounting to a virtual contradiction of the simultaneous results of direct combustion; but Johnson, on the other hand, gives results, to be cited farther on, in which the evaporative power, as determined by experiment, and the results of the litharge test closely agree. It may, however, be urged with some degree of fairness that too small. a sample of the coal is taken for examination for us to be able to draw any useful conclusions as to the properties of the mass of the coal from the results; but this argument is equally valid when used against any laboratory process, such as the ultimate analysis, or the determination of the calorific power by a calorimeter; yet if care has been used in selecting lumps of the coal which represent the average character, and then these lumps are finely powdered and intimately mixed, any part of this will fairly represent the average quality of the mass; or we may follow the course prescribed for the assay of an iron ore. Break up in an iron mortar forty or fifty pounds of the coal into pieces that will pass through a sieve with one-half inch meshes. Thoroughly mix the fine and the coarse. Now break up about ten pounds of this mixture so that it will pass through a sieve with onefourth inch meshes. Mix well: take one pound of this and pulverize until it will pass through a sieve of sixty meshes to the linear inch. Mix well: take out fifty grams, pulverized in agate mortar and pass through muslin bolting cloth. Of course in the analyses given the whole of this course of procedure was not followed, as we sought only to test the accuracy of the method by concurring results and not to analyze the coal. L. Gruner has also arrived at the conclusion that the calorific power of a coal cannot be accurately determined by its elementary analysis. He holds that a more correct estimate of the heating power of a coal is obtained by determining the average amount of coke which it yields. The higher the yield of coke the greater is the heating power, but this heating power does not diminish in the same ratio as the yield of coke; thus for a decrease in the yield of coke from 80.4 to 59 per cent., the heating power diminishes only from 9622 to 8215. In using the percentage of coke as an estimate of the value of the coal Gruner conflicts with other investigators who hold that it is an uncertain guide, since wide differences have been found in the evaporative power of different coals which possessed an equal average amount of fixed carbon. From the consideration of the amount of coke it will be seen that he is led to a system of classifying coals which is almost identical with Johnson's published in 1844. Distinguishing Property Coke on Appearance of Coke. He groups the different kinds of coal arbitrarily in five classes, as follows, though there is no distinctly marked division between any two. Elementary Relation Residue of Composition: of O CH O† 75 5.5 19.5 to to to 80 4.5 15 80 5.8 14.2 to to to 85 5 10 Dry coal, burning with a long flame. Bituminous coal with long flame, or gas coal. True coal, bituminous) 84 5 or smithy to to 11 4:3 0.50-0.60 3:2 0.60-0.68 coal. to 89 5.5 5.5 2:1 0.60-0.74 Powdery, or slightly caked. Fused, but deeply seamed. Fused, and tolerably compact. Fused; compact; 1 0.74-0.82 very slightly seam 91 4.5 5.5 ed. The O includes N, but the latter rarely exceeds 1 per cent, of the combustible matter. The length of the flame depends on the amount of volatile matter; the combustibility of the coal on the nature of the ash. If the ash contains iron and lime, a slag forms; if it contains alumina and silica, it remains in a powdery form, which is more favorable to the combustion of the coal. The first class, dry coal with long flame, is used for making coke. The Sp. Gr. is about 1.25. The color is usually brownish. A proximate analysis gives Coke. Ammoniacal liquor. Tar. 50-60 12-5 Gas. Volatile matter. 18-15 20-30 per cent. 50-40 per cent. Calorific power, 8200-8300. As soon as the carbon exceeds 80 per cent. and the oxygen is under 15 per cent., this class of coals begins to coke on heating. (2) Bituminous coal with long flame (gas coal).-The coke obtained from this coal is always caked together. The coal itself is hard, the fracture laminated. The Sp. Gr. is 1.28-1.30. Color, pure black, with strong luster. Proximate composition Coke. 60-68 Ammoniacal liquor. Tar. 15-12 Gas. 20-17 per cent. Volatile matter, 40-32 per cent.; Calorific power, 8500-8800. (3) True Bituminous, or "Smithy Coal."-Color, pure black, with high luster; brittle, with laminated fracture. leaving the coke in a compact cake. Sp. Gr. 1.3. Fuses when burning, Gas. 16-15 per cent. Volatile matter, 32-26 per cent.; Calorific power, 8800-9300. (4) Bituminous coal with short flame, or "Caking coal."-This class exhibits the same properties as the previous one; its luster, however, is not so great. It is very brittle, and although it is termed dure in France, this means that it does not burn away quickly. It does not contain much volatile matter, and is consequently difficult to kindle. Sp. Gr. 1.30-1.35. Proximate composition— Coke. 74-82 Ammoniacal liquor. Tar. 10-5 Gas. 5-12 per cent. Volatile matter, 26-18 per cent.; Calorific power, 9300-9600. One kilogram of this coal evaporates 9.75 kilograms of water. (5) Anthracite Coal.-This coal forms the link to pure anthracite. It is black, and shows dull streaks. Its cohesion is slight, but increases the nearer it approaches the character of pure anthracite. Sp. Gr. 1.35-1.40. Proximate composition |