CURRENT TOPICS.

Caliche.--D. G. RUNNER in an article in Roads and Streets for June 1935 presents information on the origin, properties and use of caliche. The material is a calcareous formation of varying thickness widely found in the semi-arid regions of the southwestern United States. It is being used in road construction in the southwest due partly to the lack of other road materials of suitable quality, and to excessive cost of shipped-in aggregate.

In western South America, the name caliche is applied to the deposits of crude soda-niter. In southwest United States it is essentially a lime carbonate, containing in addition, magnesium, alumina and calcium silicates, and is in decided contrast with the true caliche of Chile. The material possesses the property of hardening when wet, which feature is commonly utilized in con- structing pavements. However, the scarcity of water in the arid sections made it necessary to obtain the desired compaction by other methods. It was found that crushing the caliche to smaller sizes aided somewhat in the dry compaction, and the finer the material was crushed the greater the ease of compacting when in a dry state. Usually the specifications for a caliche base require the material to be put down in two courses, the first course to be throughly wet and compacted before the second course is begun. The loose material laid at least 9 in. in depth, compacted to a thickness of 496 in. The caliche, after wetting and rolling is allowed to “set up” before the second course is placed. Before putting on the top course, the base section is bladed even and brought to grade. The top course procedure is essentially the same as that employed in constructing the bottom course.

IX. H. 0.

Automatic Steam Turbine. ---R. W. P. LEONHARDT (Power, Vol.

79, No. 6). In the new power house of Mitteldeutsches Kraftwerk, Magdeburg, Germany, house service energy is supplied from the 10,000 volt main station bus bars through 3 transformers which step down to 380 volts. For emergency service a 3,000 r.p+m., 400 lb. pressure, 770 degree turbine connected to a 700 Kva generator is connected in parallel with the transformers. It is arranged for automatic starting so that it is possible to have the unit supplying energy to important auxiliaries within 30 seconds. When the voltage fails across the 10,000 volt bus bars an under voltage relay

281