July, I94O,] CURRENT TOPICS. 147

and gravel piles are usually wet under the surface and because road building so often has to wait upon the natural drying of the bot tom surface before the top course will adhere to it satisfactorily, highway depar tments have shown interest in Kotal. The final proof will come when the spring thaws have had a chance to a t tack eighteen experimental road strips in eight different states. Tests by the National Crushed Stone Association on an experimental track paved with Kotalized and untreated asphalt, indicate tha t "K o ta l mixes made with wet stone were superior to the s tandard Amiesite mixes made with dry stone." Until patents are granted the precise chem- ical constitution of Kotal will not be revealed, but a cheap waste product was needed in order to compete with the cost of stone drying and today the material cost is found to be 12 to 16 cents per ton of mix.

R. H. O.

New York's Brooklyn-Battery Tunnel.--( Engineering News- Record, Vol. 124, No. 12.) Recent arrangements for financing of the twin tube vehicular tunnel in New York City between the Bat te ry in Manhat tan to Hamil ton Ave. in Brooklyn, have advanced plans for an early s tar t on construction. Each of the tunnels will consist of a circular cast iron shell, lined with concrete, similar to the Hol- land, Lincoln and Queens-Midtown tunnels. Roadway width will be 21 ft., with annual capacity set at 16,ooo,ooo vehicles. Present traffic through the Holland Tunnel is about 13,5oo,ooo. Except for about 200 ft. at the Manha t tan end and I,OOO ft. at the Brooklyn end, all of the subaqueous part of the tunnel, some 5,ooo ft., will be in rock. Maximum depth below the water surface is 115 ft. at the Governors Island shaft. The Manhat tan ventilation building will be made to appear as one of the row of buildings tha t front on Ba t te ry Park. At the Manhat tan end traffic will not only be con- nected to the West Side Elevated Highway, which will be extended 2,5oo ft. southward from its present terminus at Duane St., but it will have access, through a tunnel around the rim of Ba t te ry Park, to South St., down which it is proposed to extend the East River Drive. The Brooklyn connection from the plaza south to the Belt Parkway at Owls Head Park, nearly 4 mi., will be built by the Tri- borough Bridge Authority.

R. H. O.

The Preparation of High-Puri ty Iron on a Large Laboratory Sca le . - - I t was found impossible to supply the needs of the National Physical Labora tory (Great Britain) by the existing apparatus. Accordingly an equipment was provided, a short account of which

I48 CURRENT TOPICS. [J. F. I.

is given by Frank Adcock in the Journal of the Society of Chemical Industry, Vol. 59, No. 2. I t is capable of producing 500 g. of finished iron per working day. Commercial electrolytic iron was converted into ferrous chloride, which was then treated with super- heated steam to obtain iron oxide. The finished iron was produced by the hydrogen reduction of the oxide and the subsequent vacuum fusion of the metal. Difficulties were experienced in the provision of suitable refractory crucibles, but these were overcome by the use of sintered alumina.

R. H. O.

Superposed Turbine Blade Research.--( Combustion, Vol. I i, No. 9.) F . T . Hague of the Westinghouse Elec. & Mfg. Co. de- scribed before the Philadelphia Section A. S. M. E. recently a re- search s tudy initiated in order to develop a bet ter understanding of the conditions affecting the operation of impulse blades in a super- posed turbine. Nothing short of actually photographing the blades' movements under actual operating conditions promised to give ade- quate and accurate records of the stresses imposed on these blades. To accomplish this an ingenious optical method was devised and the turbine blades are made to write their own s tory on a camera film adjacent to the turbine. T iny mirrors are mounted inside eight different blades in the first and second blade rows. A light beam projected through a hole in the turbine shaft is reflected by an in- clined mirror to the mirror in the whirling blade being photographed and then back out through the shaft to the s ta t ionary camera or viewing screen. By taking pictures every one-half second on a moving film, an exact record of blade performance is obtained for any desired set of operating conditions. Examination of a typical photographic record of a blade's movements during one complete revolution of the spindle shows tha t the blades vibrate like a tuning fork. The vibration is increased as a blade enters the steam jet, it vibrates while in the jet, and then continues to vibrate with slowly decreasing ampli tude after it leaves the jet. This slowly decreasing ampli tude of vibration is significant because it is caused by the in- ternal molecular friction of the blade material. The blades vibrate a t their natural frequency. This is true whether the steam shock is light or strong and is independent of turbine speed. The natural frequency of vibration is fixed by the blade design and by the material .

R. H. O.