ported entirely within the tube and free wire in the previous experiment, and to rotate, by a similar cup (surmounting passing the current, rotation occurred, a fixed vertical brass rod) at the lower showing that the chief use at least of the end of the tube, the upper end of the coil current was to impart longitudinal axial wire being kept in position by a magnetism to the axial wire, and that vertical brass rod fixed above the coil, the rotation was not simply due to any and terminated at its lower end by a sharp point of platinum in the mercury cup. A current from 6 one-pint Grove's elements arranged as 3 being now passed through the coil, brass rods, and axial wire, the latter rotated rapidly. reaction between the coil and that wire. Reversing the direction of the current did not reverse the direction of rotation. In another experiment similar to this, I formed about 12 centims. in length of the middle part of the axial wire of copper instead of iron, and obtained similar rotation; but as copper is only slightly capable of acquiring longitudinal magnetism from a coil current surrounding it, a precisely similar apparatus having an axial wire composed entirely of that metal would not rotate. These experiments and the following ones produce a striking effect in a lecture, because the rotation appears to be produced without reaction of the moving part of the apparatus upon any external or fixed body. With a downward current through the axial wire, and north poles* at the ends of the tube, the upper end of the wire rotated in the same direction as the hands of a watch. Reversing the direction of the current either in the coil or iron rod, reversed of course the direction of motion. The rotation in this case was not due to obliquity of coil-current, because that was neutralized by the second layer of coils; nor to portions of transverse currents proceeding to or from the brass rods, because each of To determine whether the longitudithose portions was 10 centims. distant nal element of the coil current obtained from the ends of the axial wire; nor was by obliquity of winding of the wire it due to the portions of current entering might be substituted for the longitudior leaving the coil, because they entered nal current through the magnet, I took and left at the same part and in parallel an iron wire 13 centims. long and 1.7 directions, and thus neutralized each millim. diameter, sharp-pointed at its other's effect. A copper wire substituted for the iron one would not rotate, probably because copper is so little capable of acquiring longitudinal magnetism. To ascertain if the rotation was merely due to an action of the current in the coil upon either the axial current or longitudinal magnetism of the iron, or whether the coil current simply performed the function of longitudinally magnetizing the axial wire, I took an iron wire 23 centims. long and 2.7 millims. diameter, sharp pointed at its lower end, soldered to its upper end a double wire of cotton-covered copper, each wire being 1.7 millim. diameter, coiled the double wire upon the axial rod in two layers (so as to enable two similar poles to be formed at the extremities of the axis), and terminated the copper wires by a little brass mercury cup just above the top end of the vertical iron axis. By supporting this apparatus as the axial South, and by a South one that which seeks the *By a North pole I mean that which points to the North. lower end, soldered near to that end one extremity of a cotton covered copper wire 1.7 millim. in diameter, coiled the latter in one direction to the middle part of the iron wire, then reversed the direction of winding and coiled to the other end of the iron, and terminated the coil by a little brass cup just above the upper end of the iron wire as before. By supporting this apparatus as in the previous experiments, and passing the current, rapid rotation took place, proving that a longitudinal current in the iron itself was not necessary. To ascertain whether the longitudinal element of the current was essential to the motion, I constructed a similar apparatus to the last, but instead of attaching the upper end of the coil wire direct to the brass cup, I continued the copper wire vertically downwards to the bottom of the coil, to neutralize the effect of obliquity of winding; then carried it outwards and upwards in the form of a the coil and on to the mercury cup. On large rectangle 5 centims. distant from passing the current rotation occurred right-handed or left-handed ( ~)*, acfreely, showing that the longitudinal cording to the direction in which its coils current was not essential to the motion. were wound. It follows from this that This experiment, and that described in a current, the direction of which is alparagraph 4, appears to prove that the ternately reversed, will drive the apparotation is not an effect of any obliquity ratus quite as well as one in one uniform or spiral arrangement of the axis of the direction. magnetized iron molecules with regard to the axis of the wire, produced by the combined action of the transverse and longitudinal elements of the current in the coil, because the latter element was neutralized, but that it is an effect of the tangential poleless magnetism in the fixed wires above and below upon the longitudinal magnetism of the movable iron axis and its coil. As an electric solenoid, however, possesses in some degree many of the properties of a magnet, its longitudinal magnetism, though feeble, must have operated in some of the previous experiments; and I therefore now tried to obtain rotation of one by the action of vertical currents. Upon a very thin wooden tube 15 centims. long and 12 millims. external diameter, I coiled a single stout cotton-covered copper wire from one end to the other, reversing the direction of winding at the middle of the tube, and surmounting the upper end of the wire by a small brass cup containing mercury. The lower end of the wire was sharply pointed, and the coil was supported as in the previous experiment. By passing the current from 6 one-pint Grove's elements arranged as 3, faint signs of rotation were observed. As the rotation was apparently due to the influence of the tangential poleless magnetism of the portions of vertical current in the fixed conductors upon the longitudinal magnetism of the vertical iron axis and its coils, I now endeavored to increase the effect. For this purpose I substituted for the upper brass rod a fixed coil consisting of one layer of copper wire upon an iron wire axis, but having dissimilar poles at its ends and no poles at its middle part, and placed between it and the lower brass rod a similar right-handed one to that described in paragraph 6 and free to rotate. The opposed poles of the fixed and movable coils were of opposite kinds, i. e. north and south. On passing a current from a Noe's thermopile of 96 elements † connected as 24, rapid rotation in a righthanded direction occurred. I now substituted for the lower brass rod another fixed coil, similar to the upper one, but of an opposite direction of polarity, and passed the current again; still more rapid rotation in the same direction took place, and the effect was very striking. In this latter instance two south poles free to move were opposed to two fixed north poles, and in each instance the current was passed upwards. In the second In each of these cases of rotation an experiment also the longitudinal magupward vertical current entering a lower netic influence of each opposed iron axis south pole or leaving an upper one and coil acted upon the tangential magcaused the upper end of the rod to rotate netism of the longitudinal element of in the direction of the hands of a watch, the end of the copper coil current opand a downward current entering or leav-posed to it, and thus both the longitudiing a north pole also produced that nal and the tangential magnetism of direction of motion, and reversing the poles in either case reversed the effect. In each of these instances of rotation, without the aid of a current near the middle of the magnet, the coil being so constructed that the current in it could not be reversed without reversing that in the fixed conductors near it, reversing the direction of the current did not reverse that of the rotation, because the two acting influences were reversed together; and therefore each apparatus had its own direction of rotation, either each of the four opposed ends co-operated to produce a most effective result. With a thicker axial wire in the moving coil the rotation was not so rapid; and with an axial wire of the usual thickness, but a double layer of copper wire coils, and the current passing through the axial wire, the rapidity of rotation was not much altered, probably because the end of which rotates in the same direction as the By a "right-handed" coil, I mean one the upper hands of a watch. I have found this apparatus very convenient for such experiments. increased weight and friction counter- current from the thermopile produced : very rapid rotation. This result proves that the rotations are not due to terrestrial magnetic influence. As the directions of magnetic polarity, electric current, and rotation agree with those in the different forms of Ampère's experiment, and as in most, if not all, of the previously known cases of rotation of a bar magnet or conducting wire on its axis an electric current passes through the end of the bar or wire, it is evident that those rotations were due, not only to the portions of current in the mercury and fixed conductors connected with it near the middle of the magnet or wire, but also to the influence of the currents in the fixed conductors near the ends of the magnet or wire. acted the effect of the increased magnetism. By substituting for the righthanded movable coil with south poles at its extremities, in these experiments, a left-handed one with north poles at its ends opposed to north poles of the fixed ones, and passing the current, no rotation occurred in this case the longitudinal element of the current in the movable coil, acting upon the longitudinal magnetism of the fixed iron axis and its coil, tended to produce rotation in one direction, and the longitudinal magnetism of the movable axis and its coil, acting upon the longitudinal element of the current in the fixed coil, tended to produce rotation in the opposite direction. I now substituted for the movable coil a vertical wire of iron 13 centims. [NOTE. It having been suggested by long and 1.7 millim. diameter, sur Professors Maxwell and Stokes that the mounted by a small brass mercury cup, rotation in the foregoing experiments passed the current from the thermopile, was due to the influence of the portions and obtained rotation, but less rapid of current in the cups of mercury, or in than before, probably because of the less the fixed conductors near the ends of the degree of longitudinal magnetism; but movable wire or magnet upon the movaby enclosing this wire in the axis of a ble magnet, I diminished the internal fixed coil which produced appropriate diameter, both of the upper and lower and similar coils at its two ends, as in cups, from 4 millims. to 1.75 millim., and paragraph 4, and repeating the experi- arranged the following apparatus and ment, very great velocity of rotation was experiment. obtained. Rotation of a somewhat thicker wire of nickel was also obtained, both with and without the aid of the current in the middle fixed coil. I also tried, without the aid of the middle fixed coil and with it, a copper wire of similar dimensions to the iron one, and obtained rotation freely; in this case the motion was probably nearly wholly due to the action of the longitudinal magnetism of the adjacent ends of the fixed axial wires, and their coils upon the tangential magnetism produced in the movable copper wire by the axial current. Each of these rotations agreed in direction with those of the movable coil. The fixed upper wire was of brass, 2.5 millims. diameter and 60 millims. long; it had no coil upon it, and was used as a conductor only; its lower end terminated in a fine point of a steel needle projecting 6 millims. The lower fixed wire (also used as a conductor only) was of platinum, to resist the action of the mercury; it was 2.3 millims. diameter and 75 millims. long, with a cavity in its upper end 3.5 millims. deep and 1.75 millim. diameter, and containing a thin plate of ruby in its lower part, with a minute hole in the center for the needle point to rotate in. The movable wire was 2.5 millims. diameter and 125 millims. long, I also obtained rotation of the iron its upper half being composed of soft wire whilst the wire was in a horizontal iron and its lower half of brass; its lower position, its ends resting in hollows in end terminated in a needle point like the ends of the iron axis of the two that of the upper fixed wire, and its fixed coils, and the ends of those axis upper end had a cavity and perforated and of the movable wire lying upon the ruby plate like that in the lower fixed surface of pools of mercury in small wire. A voltaic coil 60 millims. long and watch glasses. The movable iron wire was enclosed in the axis of a thin iron tube within a fixed coil, having appropriate and similar poles at its ends. The 7 millims. internal diameter, composed of four layers of cotton covered with stout copper wire, was used to magnetize the iron half of the movable wire, and nace : Silica.. Alumina A. B. 47.91 62.95 30.17 25.23 oxide.... 12.16 3.12 0.38 0.28 1.41 0.46 THESE experiments were undertaken at the temperature prevailing in the furwith the object of ascertaining what relation exists between the composition of the fused slag resulting from the combustion of coke at a high temperature and the deterioration of the fire bricks subjected to the action of such slag. At the same time and for the purpose of comparison, analyses were made of the ash produced by the same coke when burned at a lower temperature. It has been usual, in investigating the action of the slag produced by fuel upon fire-proof materials, to analyze the ash of the fuel before it has undergone fusion. That such a practice must, in many cases, lead to erroneous conclusions may be seen from the examples given below. The The fused slag formed a dark glass of experiments were conducted in regener- the specific gravity 2.52, and enclosing ator furnaces for heating gas retorts. globules of metallic iron. At the higher In these furnaces the fire bricks, espec- temperature, therefore, both iron and ially in the neighborhood of the slits through which air is admitted, are very rapidly corroded, unless their composition is adapted to the acid or basic nature of the slag with which they are brought into contact. 100.01 manganese had been reduced to lower stages of oxidation, part of the former even to the metallic state. The sulphates of lime and magnesia had been either volatalized or removed by mechanical means, and the potash and soda reThe first series of experiments was mained in the slag. Although the ash made with a regenerator furnace on is of a decidedly basic character before Müller and Eichelbrenner's system. fusion, yet the slag produced from it is The coke used was from the Gelsenkirch acid. In this case the use of fire bricks district, and contained 11.92 per cent. of with an excess of acid constituents was ash. When produced at a temperature indicated. Those used contained 89 per which did not suffice to fuse it, the com- cent. of silica, and resisted the action of position of this ash was that given under the fused slag remarkably well. A. B is the ash of the same coke fused In the second series of experiments the regenerator furnace was constructed phates present. This furnace was lined on Liegel's system. The coke was made with fire bricks containing as high a profrom a mixture of Nettlesworth and portion of alumina as possible; they reLeverson coal. The proportion of ash sisted the action of the basic slag so in the coke was 9.24 per cent.; its well that their wear was almost imperanalysis is given in the following table ceptible. under A. After the furnace had been working for three days the sample B was taken. It was but partially fused, the action of the furnace being imperfect, owing to the air slit being too large. When this had been reduced in size the slag was easily fused, and had the composition C: The coal used in the third series of experiments was from Upper Silesia, and contained 3.54 per cent. of ash, of the composition given below under A: Silica.... B. A. 61.18 61.32 26.07 23.79 oxide.... 7.32 66 7.41 Potash Loss as gas.. Manganous 0.25 Lime... The apparent excess in B is due to the oxygen of the iron and manganese com--Journal fur Gasbeleuchtung. pounds, part of which were present in the lower stage of oxidation. The presence of titanic acid is remarkable in these analyses. The changes which took In the early future india-rubber ought place during the first stage of fusion (B) not to be an expensive article. Accordwere not important. In the second ing to information concerning the plant stage (C), when completely fused, the which produces Ceara rubber, contained slag became more basic in its character in the report on india-rubber by Dr. than the ash from which it was derived. H. Trimen, of Ceylon, the plant is very There was a considerable reduction of metallic iron, which was found in numerous globules interspersed throughout the dark, vitreous mass. In this case also the sulphates had been volatilized. The iron globules were very impure, containing only 36 per cent. of metallic iron. hardy, and will grow in a dry, rough soil, and a moderately dry, hot atmosphere, while the Para and West India rubber plants require a rich alluvial soil, and a constantly hot-moist atmosphere. Ceara-rubber plants have been found to succeed in Ceylon, Calcutta, and Madras, After the furnace had been in work but the climate of Singapore is too wet some months the draught became defect- for them. It is suggested, says the ive, and, on the flues being opened, Journal of the Society of Arts, that they were found lined with a 2 inch coat- plantations should be formed on exing of a light, porous substance, which hausted coffee land. The tree grows to was found on analysis to contain 72 per about thirty feet or more in height, and cent. of silica and a large proportion of forms a dense rounded crown. It atsulphates. It probably owed its origin tains a diameter of four inches or five to the decomposition of the slag by inches in about two years, when it may steam, assisted by the action of the sul- be tapped. |