I 2 2 CURRENT TOPICS. [J. F. i.

itself is made the resistor. The use of the Hflberger furnace for brass melting is said to be inconvenient and expensive on account of the short life of the crucible. The Hering furnace, also, operates on the resistance principle, but in this case the metal itself is the resistor, and this introduces difficulties with metals like copper which have high electrical conductivity. The induction furnace, also, can only have a limited application to the melting of non-ferrous metals on account of their usually high electrical conductivity.

G. H. Clamer and Carl Hering have described very fully the use of the Hering " pinch effect " furnace for melting brass. The power consumption, when melting light brass or bronze chips, was found to be 25o kilowatt-hours per short ton of brass melted. This furnace was to be introduced at the foundry of the Ajax Metal Com- pany in Philadelphia. H . M . St. John has given information with regard to the electric melting of brass. Two types of electrical resist- ance were employed--the " crucible lift out" type and the tilting type. With the tilting furnace, 280 kilowatt-hours are needed per ton of yellow brass, and 350 kilowatt-hours per ton of red brass, in continuous melting. If the power is only used for ten hours daily, the power consumption will be 40o to 5o0 kilowatt-hours respectively. With the crucible lift-out furnace, the power consumption is 43 per cent. more than the foregoing figures.

For the economical melting of copper, brass and other metals and alloys, the arc furnace appears to be, the most efficient, but in arc furnaces there may be a serious loss by volatilization of metals like zinc, tin, and even copper, while the temperature is far less easily controlled than in the case of resistance furnaces. Messrs. Lyon and Keeney review the furnaces available for the electrical melting of copper and conclude that the Heroult steel furnace is the most suitable. The writer has had some experience with the Ren- nerfelt arc furnace, and considers this perhaps the most promising type of arc furnace for melting copper, brass and the non-ferrous metals generally. The Rennerfelt furnace has three graphite elec- ,trodes, one vertical and two horizontal, which ,meet in the middle of the furnace. These are supplied with two-phase current, the ver- tical electrode being the common return for the other two. This fur- nace, like S:tessano's, has the advantage of an arc that is independent of the material to be melted, but the efficiency is better in this case owing to the downward direction of the flame.

Gasoline From Oil Shales. ANON. (U. S. Geological Survey Press Bulletin, No. 3o0, December, I916.)--In anticipation of the day when, on account of the advancing cost of gasoline and other products obtained from petroleum, it might be found commercially profitable to utilize some of the enormous supply of petroleum to be derived from the distillation of the vast deposits of so-called hydro- carbon shales of the Green River formation of northwestern Colo- rado and northeastern Utah, the United States Geological Survey

J a n . , 1917 . ] CURRENT TOPICS. 123

has for three years been making field investigations of these deposits. The examinations have been accompanied by mapping of the areas of hydrocarbon shales and by such field measurements of the thickness of the shales in workable beds and such rude field distillation tests as will afford primary information concerning the amount and richness of the shale in different parts of the region.

Very rough bu,t cautious calculations of the contents of the shale in parts of the area examined indicate that the distillation of shale from beds over 3 feet thick in Colorado alone will yield more than 2o,ooo,ooo,ooo barrels of crude oil, from which more than 2,ooo,- o0o,ooo barrels of gasoline can be extracted by ordinary methods. A report giving the results of these explorations and tests and an account of experiments as to possible gasoline production, both by the ordinary commercial processes and by the Rittman process, are now in press.

Close-Plating. C. H. POLAND. (Metal Record and Electro- pla, ter, vol. ii, No. I i, November, i916.)--Close-plating, an art prac- tised for centuries, is carried on now to a very limited extent, and will soon be classed as one of the " lost arts." Till recent times it was regarded as one of the most important industries but it has gone down before the advance of electroplating. A few score years ago close- plating was the only method by which an article could be given the appearance of the precious metals, as all articles plated with either gold or silver were plated by this process. The massive door knobs, name plates, escutcheons, ornaments and tableware found in colonial houses, that were not of solid gold or silver, were all close-plated.

The process consists essentially in soldering on a carefully fin- ished and tinned piece a thin sheet of soft silver shaped to fit the work. The silver sheet is stretched and worked into the crevices until it fi.ts the part closely and then soldered. All these operations are performed with the simplest tools, but consummate skill and rare judgment are essential in the practice of the process.

Elect rolyt ic Cleaning of Silverware. ANON. (Metal Record a,zd ElectropIater, vol. xi, No. ~t. November, I916 . ) - -A bulletin recently published by the United States Department of Agriculture deals with the electrolytic method of cleaning tarnished silver, which is recommended as an easy and effective way of performing this task. It consists in boiling the article in a soda and salt solution in contact with a clean piece of aluminum or zinc. Experiments made under the direction of the Bureau showed that when silver spoons were polished with whiting paste, nearly o.oi grain of silver each was lost, whereas with the electrolytic process, only one-twenty-fifth of this amount was wasted.

The tarnish which occurs in silver is not due to oxidation, but to the action of sulphur. The electrolytic cleaning depends upon the slight solubility of the silver sulphide in the hot solutions employed,