CURRENT TOPICS. 409

and machined products. Graphitic grains form centres from which rusting starts. Fractures rust more readily than the outer surface, and it is suggested that a coating of silicates in the case of cast iron, and films of scale in rolled material, act as a protecting layer. The rough surface of a fracture distinctly accelerates rusting. Smooth surfaces are more resistant than rough ones.

Hardening Copper. (U. S. Pat. No. 984,I37.)--R. A. Hamil- ton and J. Henry harden copper by treating it with a mixture of aluminum and iron pyrites. The aluminum is heated to a high temperature in a crucible and enough pyrites added to it to form a brittle compound, which is poured into moulds. From I to 3 oz. of this mixture, with charcoal and borax, are added to each pound of copper already melted.

Electric Smelting of Iron Ore at Trollhdtten, Sweden. ANON. (Board of Trade J., June 29, I 9 I I . ) - - T h e report of the Swedish "Jernkontore t , " or Iron and Steel Institute, for I9IO, gives the re- sults of the experiments made at Trollh~itten in the smelting of iron ore by electricity, provided at low cost from the Government works. The plant cost £17,8oo. Operations began Nov. 15, 191o. The results show that the question of smelting iron ore by electricity is solved even from the economical point of view, if electricity is pro- vided at low rates. Better results are expected if the gas can be more effectively circulated, which seems feasible with better arrangements. The experiment has paid expenses. It is considered that the smelt- ing works cannot be a commercial success if the cost of electricity should exceed the present rate of t;2 4s. 5 d. ($Ii.OO) per kilowatt per annum. In a five months' run the consumption of charcoal was 413 kilos per ton of iron, and of electricity I kilowatt per annum for 4 tons. The product was practically free from slag and oxide. Satisfactory results were also obtained at the works at Fagersta, Eskilstuna, Hagfors, and Munkfors.

Mineral Resources and Industry of Bolivia. ANON. (Board o[ Trade J., July 6, I9 I I . ) - - Ind ica t ions of gold are found all along the eastern slope of the Cordillera Real, and in the beds of the rivers flowing east from this range. The annual production of gold in Bolivia may be reckoned as 17,46o ounces of bullion, value at £72,ooo. The richest silver region lies in the west. In the north, south and east the silver lodes are found near the summits of the Andean range, running east and west. There is little silver in the nor th . The production of silver fell from £I,474,49~ in 1895 to £54,472 in 19o 9 . This diminished output is attributed to the fall in the price of the metal, and the increase in the value of tin, which is abundantly found close to the silver-bearing areas and in an easily worked con- dition. The silver mine owners have diverted their work and capital to tin production. Copper is found widely distributed over the