The concentrator apparatus consists of a balance or storage tank in elevated position according to whether the closed or open system is used; one or more stands of pipe coils; a catch pan for concentrated brine; a reservoir and a small pump for passing brine into system. The brine flows from storage tank, entering the bottom pipe of the coils and passes upward through seventeen pipes, from which point it is delivered to the trough at the top of the coil and allowed to flow down over the entire battery of pipes, steam being circulated through the top six pipes, thus heating the brine and concentrating it by evaporation. The hot concentrated brine is cooled as it passes over the lower seventeen pipes through which it originally entered as cold weak brine. =Direct Expansion.=--Many plants are equipped completely with direct expansion systems. This is quite satisfactory provided means are arranged to dispose of the accumulating ice and snow on the coils. This is particularly applicable to coils in pipe lofts where moisture rapidly accumulates, and is accomplished by some arrangement of defrosting such as circulating a brine over coils by permitting it to drip over the coils, pumping over and over again. =Two-Stage Compressors.=--The revising editor brought into prominence the two-stage compression system by building a successfully operating plant which functioned with quite astounding results. The system consists of a large low temperature gas compressor and a smaller second stage compressor, arranged the reverse to a compound steam engine. Ammonia gas which at the low temperatures resulting when low back-pressures are required, becomes highly attenuated (light), it is necessary to handle a very large volume per ton of refrigeration developed. To provide for this, the low pressure cylinder is made about double the volume of the high pressure cylinder. In the low pressure cylinder the gas is compressed to a pre-determined pressure and passed at a relatively high pressure, making for a very high efficiency. The gas is chilled by the introduction of expanded ammonia to take up the superheat. The use of this compressor arrangement with its refinement makes an economical cold producing unit. A record of one year’s run follows: TWO-STAGE COMPRESSION SYSTEM. Per Per year. ton. Tons received 60,000 Cu. ft. space cooled 2,930,000 Coal cost $17,309.11 .288 Labor 15,156.73 .252 Oil and waste 1,030.82 .017 Water and chemicals 2,103.21 .035 Repairs and changes 1,698.38 .028 ---------- ---- Total cost $37,298.25 .62 Expense per cu. ft. space per year .013