SOME NOTES ON ELECTRIC RAILWAY TESTS.* Prof. Herman S. Hering presented to the Section "Some Notes on Electric Railway Tests," of which the following is an abstract, and which should prove of great value, and well worth the great amount of time and labor spent upon the collection of the data on which they are based. The first point discussed was the importance of intelligent management of the controller by the motorman in order to obtain the best results. Starting too suddenly must be avoided, not only out of consideration for the comfort of passengers, but also because the mechanical strains would be serious and the motors would be working inefficiently. On the other hand, the cars must not be started too slowly, for the reason that the motors would work at a point of low efficiency, and also because the time of the trip would be lengthened. The cars should be allowed to "drift" as much as possible, so as to avoid waste of energy when brakes are applied. Experimental trips, under careful observation, made with an expert and a non-expert motorman, under similar condi tions, demonstrated that the expert accomplished the trip with the same number of stops and passengers as the nonexpert, and with a saving in energy used of from 15 to 25 per cent. On a ten-mile road running fifteen cars, the saving from this source would amount to about $810. The speaker next discussed the question of the loss of energy due to the sparking of the trolley wheel. This was found to be, for old wheels, as much as 250 watts; and for new wheels, 60 watts. Insufficient tension on the spring was said to be responsible, generally, for this loss, which may be obviated by careful inspection and adjustment of the springs. The loss from imperfect contact between rail and wheels *Abstract of remarks made at the stated meeting of the Electrical Section of the Franklin Institute, held September 24, 1895. was also determined, and, in the case of a track slightly sanded, was found to be about 04 horse-power. RECORDING AMMETER AND VOLTMETER. At the same meeting, Professor Hering also described a "Recording Ammeter and Voltmeter," devised by him, for use in the tests above referred to. As described by the speaker-and illustrated by sketches on the blackboard-this instrument consists of a Weston apparatus, in which the needle moves over a sharp metallic edge, with a strip of paper sensitised with calcium chloride between the needle and the sharp edge of the metal. One terminal of a small induction coil is connected to the needle, the other to the metallic edge, and the record is made by the spark in its passage through the paper from one to the other. The speaker exhibited curves taken with the instrument. THE JOHNSTON RAIL-BOND. At the same meeting, Mr. A. Langstaff Johnston exhib. ited several specimens of his rail-bond, which had been removed from the road-bed of the Hestonville Passenger Railway Company, Philadelphia. Mr. Johnston stated that the rails to which these bonds had been attached had been down for two years. The contacts between the iron of the rail and the metal of the bond, on the specimens shown, appeared bright and clean. From the experience with the bond gained on the line of this railway, Mr. Johnston stated that soldering the bond to the iron, which was originally done, had been found to be unnecessary. CHEMICAL SECTION. Stated Meeting of October 15, 1895. DR. WM. C. DAY, President, in the Chair. CARBIDES OF IRON. BY F. LYNWOOD GARRISON. In reviewing the history of the metallurgy of iron and steel, we find that ever since the recognition of the important role which carbon plays in the economy of this impor. tant industry, great efforts have been made to explain the phenomena, presumably due to carbon, which accompany certain metallurgical operations. The mere fact that carbon was known to exist in the metal in two distinct forms, graphitic and combined (the latter so-called for want of a more scientific definition), was not sufficient to explain to the inquiring mind such changes of molecular structure as take place in the cementation furnace; and that this particu. lar problem is perhaps no nearer solution to-day than thirty years ago, is probably due, in great measure, to the fact that the process as a commercial operation has long since fallen into disuse. It has, of late, however, cropped up in a somewhat different form in the methods of facehardening armor-plate by the addition of carbon, and possibly of chromium. Although, within recent years, patents have been granted for increasing the combined carbon, and thus imparting additional hardness to articles of steel, as long ago as 1830, Karsten, in his researches upon the solvent action of acids upon iron and steel, observed a carbon compound which was evidently not graphite, and which must, consequently, be considered under the equivocal head of combined carbon. He did not succeed either in preparing or separating such a carbon compound having a definite chemical composition, but his observations led him to believe that carbon united with iron in such proportions that chemical union was effected, and that the resulting body would probably correspond to the formula Fe,C. Berthier2 claimed to have obtained a definite monocarbide, FeC, by the action of iodine and bromine upon steel. His observations, however, were never confirmed, and Caron3 vainly attempted to produce this carbide by a similar solvent action of bromine, or iodine. Hence, the latter chemist concluded that the carbide of Berthier was a mixture of carbon and iron, in which the iron was mechanically protected from solvent action by the carbon. Berzelius claimed to have obtained the carbide, FeC2, by the distillation of ferrocyanide of ammonia; and another carbide, FeC, by treating pure Prussian-blue in the same manner. Whether these residues were actual combinations of carbon and iron, or only mixtures of carbon and iron slightly carbonised, is doubtful. Percy appears to regard their acceptance as definite compounds with reservation. The first investigators to isolate a definite carbide from iron, were Müller and Abel, who, though working independently, appear to have obtained similar results. Müller, like Karsten, obtained the carbide by the action of dilute sulphuric acid upon Bessemer steel, the resulting residue being pyrophoric, and containing from 601 to 7:38 per cent. of carbon. Hence he deduces the formula Fe,C. Müller remarks that, by the solvent action of the acid, a very large quantity of the total carbon must have been converted into hydrocarbons, since, by calculation, the carbon of the carbide is only from 20 to 50 per cent. of the total amount in the steel. Abel obtained Fe,C, by the action of a solution of potassium bichromate and sulphuric acid, containing just sufficient acid to dissolve the iron, since the amount of free sulphuric acid present greatly affects the yield of carbide. The carbide obtained by Abel' from several varieties of 1 Manuel de la Metallurgie du Fer (Metz, 1830), Vol. 1. p. 173. 2 Ann. des Mines (3), 3, 229. 3 Comptes Rendus 56, 44; Percy, Iron and Steel (1864), p. 122. 1 Traité de Chimie (1831), p. 270; Percy, Iron and Steel (1864), 122. Metallurgy of Iron and Steel, p. 123. Zeitschrift des Vereins Deutscher Ingenieure, 22, 385. 1 Proceedings Inst. Mech. Engs. (1885), 30–57. VOL. CXL. No, 840. 30 iron, had a somewhat variable composition, as shown in the Less than 0.93 per cent. of the water is probably present as mechanically retained moisture, the greater part being a constituent of a carbo-hydrate resulting from the decomposition of the carbide, since this increase in the proportion of water is attended by an increase of carbon and a decrease of iron. The specific gravities of the carbide are, respectively, as follows: From cold-rolled steel . . 6'9 7.2 Abel concludes that, at least in the unhardened steel, the carbide exists entirely as Fe,C. Osmond and Werth3, by submitting bars of steel to electrolysis in hydrochloric acid, and examining the residue microscopically and chemically, identified the carbide, Fe,C, observed by Abel. They obtained it in brilliant magnetic scales or plates, and also observed that when a bar of steel is heated to redness it contains, besides carbides of iron, free carbon ("carbon libre"), the proportion of the latter increasing with increase of temperature. The observations of Arnold and Read1 show that a readily decomposable sub-carbide of iron exists, the iron of which is dissolved by the solvent, whilst the carbide escapes in the form of hydrocarbons. As a result of their extensive investigations, they arrive at the following conclusions: (1) The "normal carbide " exists in two forms of identical composition; (a) a diffused carbide scattered in microscopic granules, or very small plates, yielding on isolation a 8 Ibid. 9 Ann. des Mines (8), 8, 19 et seq. 10 Jour. Chem. Soc. (Trans.), 65, 788. "They use the term "normal steel" to designate a steel heated to 1,050° C. and cooled in air. The normal carbide is, of course, the carbide from such a steel,-F. L. G. |