Jan., 1918.] CURRENT T Ol~ICS. I59

denness of the effect being such as to bring it within the realm of detonation. A large amount of information regarding explosives made with liquid oxygen is available, as this subject was extensively investigated about 18 years ago by a distinguished chemist, Sir James Dewar, in England. An experimental plant for its manufacture was also under consideration, if not actually erected, at Boston by a subsidiary of the British corporation. The investigations then made indicated favorable possibilities for the oxygen explosive, though some difficulties were experienced. Financial troubles pre- vented Dewar from continuing his efforts to commercialize the invention.

An Automatic Hydroelectric Plant. ANON. (Electrical World, vol. 7o, No. 22, p. lO42, December I, I917.)--A hydroelectric gen- erating station which is entirely automatic in all of its operations has recently been placed in service by the Iowa Railway and Light Company on the Cedar River, only a few blocks from the business district of Cedar Rapids. The plant, which will have an ultimate capacity of 2ooo kilowatts, operates in parallel with an extensive transmission system which already reaches practically across the State of Iowa, except for a 28-mile break near Marshall~wn. There are no instruments in the hydroelectric plant, these being installed in the company's steam station, which is about 0.6 mile distant. Three groups of conductors--power cables, instrument cables, and control cables--connect the two plants; hence, while the hydro- electric station is self-controlled and entirely automatic, it is pos- sible for the steam-plant operators to supervise the action of the waterwheels and generators.

Perhaps the most spectacular and surprising feature of the whole plant is the speed with which the station goes into service. It re- quires just 37 seconds from the time the first switch operates until the first generator is under full load. A somewhat formidable array of mechanism might be expected in a plant of this nature, but the contactors and switches are inclosed in cabinets and the buses and control wires are run through bus chambers beneath the floor, so that the interior of the station appears very simple. With this ar- rangement, and by making each generator and its circuits, except for excitation, an independent unit, every element of the wiring and control apparatus has been made readily accessible.

The excitation for each machine is maintained at a fixed value at all times, thus simplifying the excitation problem, eliminating the necessity of voltage regulators, making it possible to take advantage of the full capacity of the river, and at the same time improving the power factor of the system through the operation of underloaded, overexcited machines. No oil governors are used for any of the machines, the gates being operated by motors which are upon com- plete automatical control at the hydroelectric station or remotely con- trolled from the steam station.