Increase in the voltage acting upon a solid conductor increases the current through it, but in the case of the electric arc an increase in current is accompanied by a fall in the difference of potential of the carbons, within certain limits, and the arc has therefore been said to possess a negative resistance.'
By continuing the introduction of methyl groups we obtain three series of homologous hydro carbons given by the general formulae CnH2,i 4.2, CnH2n, and CnH2n 2, each member differing from the preceding one of the same series by CH 2.
The carbons can thus, by the application of suitable mechanism, be withdrawn from or plunged into the furnace at will.
When coal is heated to redness out of contact with the air, the more volatile constituents, water, hydrogen, oxygen, and nitrogen are in great part expelled, a portion of the carbon being also volatilized in the form of hydro carbons and carbonic oxide,-the greater part, however, remaining behind, together with all the mineral matter or ash, in the form of coke, or, as it is also called, " fixed carbon."
Fremont is situated in a good agricultural region; oil and natural gas abound in the vicinity; and the city has various manufactures, including boilers, electro-carbons, cutlery, bricks, agricultural implements, stoves and ranges, safety razors, carriage irons, sash, doors, blinds, furniture, beet sugar, canned vegetables, malt extract, garters and suspenders.
Two procedures are adopted: (1) graphitization of moulded carbons; (2) graphitization of anthracite en masse.
The former includes electrodes, lamp carbons, &c. Coke, or some other form of amorphous carbon, is mixed with a little tar, and the required article moulded in a press or by a die.
33 28, 3329 (1901)] prepare sodium cyanamide by melting sodium with carbons or some hydrocarbon, and passing ammonia over the melt at from 400 0 -600° C. The temperature is then raised to 700°-800° C., and the sodium cyanamide in contact with the residual carbon forms sodium cyanide.
Through stuffing-boxes at the ends passed the two electrodes, made after the fashion of arc-light carbons, and capable of being approached together according to the requirements of the operation.
Diamonds are now employed not only for faceting precious stones, but also for cutting and drilling glass, porcelain, &c,; for fine engraving such as scales; in dentistry for drilling; as a turning tool for electric-light carbons, hard rubber, &c.; and occasionally for finishing accurate turning work such as the axle of a transit instrument.
It has been found that the " carbons " in drills can safely be subjected to a pressure of over 60 kilograms per square millimetre, and a speed of 25 metres per second.