1 0 2 CURRENT TOPICS.

Hole River, about 3 ° miles southwest of Butte. It is probable that similar deposits exist over a large part of western Montana. Sul- phuric acid for the conversion of the mineral phosphates into super- phosphate could be readily obtained from the waste gases of the numerous smelters in that region.

Electric Arc Welding Processes. C.B. AUEL. (Amer. Mach., xxxiv, 479.)--This article describes fully three processes, with their limitations, the apparatus used, the range of work done, the time required, and the results obtained. It also presents suggestions and cautions for their successful application. Undoubtedly this will repay any person interested for its perusal.

Austrian Electrical Directory.--The Electro~echnical Society of Vienna is about to issue a directory of the electrical power stations in Austria and Bosnia-Herzegovina.

The number of electrical stations in Austria is about 80o and they supply current to more than 1,6oo cities and towns. The book, which will bear the title " Statistics of Electrical Plants in Austria," will contain the names of the proprietors of the plants with their addresses, the names of the architects, the places supplied with power and much other information relating to the stations, the dynamos and accumulators, the current, motive power, voltage and area supplied. The number of incandescent and arc lamps, the number of meters a.nd motors with memoranda as to their efficiency, as well as data regarding the price of current, capital invested, annual quantity of current produced, etc., will be included.

The work, which has been compiled with the greatest care, will atgpear in print about July xst, and will be issued by the Society. As this book, as well as others issued by this Society, is not a money- making venture but is intended for the use of all who are interested in electrical engineering, the price will be comparatively low, and it may be ordered at this time for 2.80 crowns, post paid. After the appearance of the directory the price will be advanced to 3.80 .crowns.

The Lost Art of Tempering Copper. ANON. (Brass World, vii, 174.) The Aztecs, Toltecs and Tarascans, it is said, possessed in pre- historic ages the art of tempering copper. Several archaeologists :and ethnologists of Mexico City now deny they had such knowledge. Copper axes and knife blades found at Atcapotzaleo are so soft they can be cut with an ordinary pocket-knife. On the other hand, Tarascan copper cutting implements from the Balsas River ruins in Guerrero were so hard that they would turn the edge of a modern ' knife. Analysis showed that these different blades were of the same composition as the copper ores found in the respective lo- ~:alities. The soft blades were made from comparatively pure copper