532 CURRENT TOPICS. [J. F. I.

of a new package ice cream vending machine in Refrigerating Engineering, Vol. 30, No. I. Previous machines of this type have experienced trouble, due to leakage and to the opening and closing of the machine at the time of the delivery of the merchandise, enough moisture entering the machine to form ice in the merchan- dise compartment, coin and delivery mechanism. Not only has this difficulty been overcome, but the final design has a mechanism that will handle five different kinds or flavors of ice cream that can be selected at will. The machine is refrigerated by cold air. A special evaporator is located in a separate compartment, with a blower for circulation of the cold air to and through the merchandise compartment, and back to the evaporator chamber. This eva- porator is so designed as to hold a 90 per cent. relative humidity in the merchandise compartment, but will not permit excess moisture to collect there. The machine operates between o” and 5“ and will go for fifteen days without defrosting. It is cooled by a 1/S h.p. hermetic compressor. At the time of defrosting, the water from the defrost is re-evaporated by the condenser heat, so that there are no drips or drains or pans of any kind. The machine pulls ISO

watts at 110 V. when it is in operation, which is about 60 per cent. of the time, at 90’ F. room temperature. It weighs 90 Ibs.

R. H. 0.

Ice Solves a Gas Distribution Problem.-The golden rule in public utility practice is to maintain uninterrupted service. At times this becomes difficult in gas distribution, especially when both normal and emergency repairs must be made on high pressure pipe lines. Mr. I. H. Witt in Western Gas, Vol. XI No. 8, describes a new process to overcome this difficulty. The initial operation consists of clamping to the pipe at the point at which it is desired to shut off the flow a suitable pipe saddle containing a gas main cock and stuffing box above the cock. The main is next drilled and tapped, working through the stuffing box and ccck, preventing any escape of gas. Next a cold pack is placed on each side of the saddle, consisting of cracked ice and salt or dry ice in canvas wrapped around the pipe. When the pipe is sufficiently chilled, a mixture of finely shaved ice and water is forced into the gas main from a specially constructed pump, the lower end of which is inserted into the main through the stuffing box and cock. The cold packs cause the shaved ice to freeze into a solid gas-tight ice block across the whole cross section of the main. When it is desired to reestablish the flow of gas the cold packs can be removed and heat applied to the outside of the main. Then the other apparatus can be removed, plugging the drilled hole with a brass plug. There is no escape of gas during the

Oct., 193j.l CURRENT TOPICS. 533

whole process. A by-pass around the area of operation allows it to be done without interruption to service. The method and ap- paratus are patented.

R. H. 0.

A New Carrier-Current Coupling Capacitator.-By means of coupling capacitators connected to high voltage power transmission lines, high frequency carrier currents in different frequency channels may be transmitted over power lines for supplementary services such as relaying, control, and communication. E. D. EBY, in Electrical Engineering, Vol. 54, No. 8, describes new coupling capacitators to be used on the Boulder Dam power transmission system of the City of Los Angeles bureau of power and light. A higher line voltage will be employed than has previously been used in this country. Several advantages favored small series connected units in contrast with a single large unit capacitator for this voltage. A survey of existing operating voltages showed the prominence of 69,138 and 230 kv. circuits, suggesting units rated at 69 kv. From a review of the 60 cycle and impulse characteristics of line apparatus and line insulation for these circuit voltages, it was found that a 69 kv. capacitator unit in series combinations of 2, 3 and 4 units, respectively, would co6rdinate satisfactorily with the insulation requirements of 138,230 and 287 kv. circuits. Since these capaci- tators were intended to serve the double purpose of carrier current coupling and potential coupling, it was necessary to consider the output demanded by both classes of service. It was found that the carrier-current demand for the 287,000 volt circuit would be pro- vided for by a capacitance of 0.00075 microfarad. Thus, with 4 units in series, the unit capacity would be 0.003 microfarad. This capacitance would also provide adequate output for potential devices-150 volt amperes.

R. H. 0.

An Automobile Fuel That Supplies Both Refrigeration and Power.-Food Industries for August, 1935 has an unsigned article describing a combination fuel-refrigeration system for food trucks. In such an arrangement propane, a gas at ordinary temperatures, cools the truck body and takes the place of gasoline. Propane is closely related chemically to gasoline, the former being classed as one of the lower paraffin hydrocarbons, while the latter, a volatile liquid, is composed of paraffins more complicated in structure. As a matter of economy, propane is supplied in its liquid form in pressure cylinders that are interchangeable. Since it boils at minus 40’ F. or lower, it is only necessary to release the pressure to bring