An ideal rubber factory

G U R R E N T TOPICS. Use of Pulverized Coal in the Cement Industry. R. C. CARPENTER. (Amer. Soc. Mech. Engin. Journal, xxxvi, p. 337.)--The author devotes a large portion of this paper to the history of the development of the process for burning pulverized fuel in cement kilns in the United States. Hurry and Seaman were the first to apply the new method successfully, in the years 1894--95, in the cement works of the Atlas Company. According to the author no inventors prior to Hurry and Seaman had comprehended the essential condition of success for burning pulverized fuel in furnaces; namely, that the fuel must be burned completely while in suspension, and that the utilization of the heat of combustion must be by radiation from the flame, and not by impingement of the flame on the bridge or walls of the furnace. The failure to recognize this condition of success is, he states, in a large measure responsible for the practical failure of the burning of pulverized fuel in boiler furnaces, although such furnaces, because of their form and proportions, render more difficult the problem of burning coal-dust in suspension. In practically all of the devices which have been tried under boilers the flame has impinged on the bridge-walls or sides of the furnace, or on portions of the boiler, before the combustion was completed, with the results that fuel was wasted, capacity was reduced, and the linings of the fire-box or other portions on which the flame impinged were destroyed. Since 19o2 the use of pulverized coal for heating the rotary kilns has become general in the cement industry, and operations and machinery used have become standardized. They are considered and described under the following headings: (I) Drying; (2) Pulverizing; (3) Conveying; (4) Storing; (5) Feeding. An Ideal Rubber Factory. A. DOUGLAS. (India Rubber Journ., xlviii, I8.)--The greatest possible cleanliness must be aimed at, and certain precautions in factory-design and equipment are enumerated. There must be no bright light, which darkens the rubber, and no dark corners to harbor fungi. Rain water should be collected and used for dilution of latex and acid. Smoke chambers should be of wood, with heavy corrugated iron roofs, lined with sacking. The procedure recommended for the production of smoked sheets is as follows: The latex is diluted to standard gravity and mixed in a white-tiled tank. From 0. 7 to I per cent. of its bulk of IO per cent. acetic acid is added, and the mixture stirred with a glass rod, and then transferred in pails to the pans, which, when full, are skimmed and dividing boards introduced. On the following morning the 366

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CURRENT TOPICS.

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coagulum is gently pressed until about three-fourths of an inch thick, then reduced to ordinary sheet thickness by three or four passages through smooth rollers, and finally once through marking rollers. The sheet is drained on racks for two hours, then smoked. Decayed timber and cocoanut husks form good fuel. The rubber is ready to pack in ten days. In making thick cr6pe the rubber is first sheeted between rollers, dried, and re-rolled thick in diamond rollers and dried further. It is ready for packing in twenty-one days. T h e Influence of A l l o t r o p y on the Metastability of Metals, and its Bearing on Chemistry, Physics and T e c h n o l o g y . E. COHEN. (Faraday Society, Nov. 23, I914.)--Experiments made with pure cadmium are described, measurements being made with the pyknometer, the dilatometer, and with low-voltage standard cells in which the negative electrode consisted of cadmium deposited electrolytically on a platinum spiral. The results show that ordinary cadmium contains three allotropic forms. Density and dilatometric measurements made with pure lead indicated for this metal also the simultaneous presence of more than two allotropic forms. The conclusion is drawn that the pure metals (Cd, Pb, Bi, Cu, Zn, Sb), as known until now, are metastable systems consisting of two (or more) allotropic forms. This is a consequence of the very strongly marked retardation which accompanies the reversible change of these allotropic modifications below and above their transition points. All the physical and mechanical constants of metal hitherto d e t e r m i n e d t h u s refer to complicated metastable systems, which are entirely undefined, as the quantities of the a, fl and 7 modifications they contain are not known. The reversible transformations of one modification to another must play an important r61e when metals are subjected to changes of temperature. If the metals are in contact with electrolytes (water), the transformation velocity is enormously accelerated, and the volume changes which generally accompany these transformations may cause the disintegration of the metals. These phenomena must be taken into account in cases where corrosion occurs. M a r t e n s i t e S t r u c t u r e of Steel. C . H . DESCI-I. (FaradaySociety, Nov., I 9 1 4 . ) - - B y slowly cooling an overheated steel (C 0.28 per cent.) a martensiticstructure was obtained without increase of hardness; by examination with an immersion objective, the whole mass was found to consist of pearlite packed closely in some parts and loosely in others. The view of Edwards and Carpenter that martensite and austenite are constitutionally identical, the former being repeatedly twinned, and its hardness due to the formation of amorphous material at the surface of slip on which twinning occurs, is rejected, and it is considered that the martensitic structure is an accompaniment, and not the cause, of the hardness of a quenched steel, martensite being so much harder than its components as to suggest the presence of a solid solution. VoL. CLXXIX, No. IO7I--24