<div class="htmlview paragraph"><b>B</b>EGINNING with a statement of the requirements of a high-temperature cooling-liquid and a short history of what had been previously done in this field, the author gives a description of the liquid used in the investigation which was conducted by the Materiel Division at Wright Field.</div> <div class="htmlview paragraph">The investigation is divided into five parts which includes dynamometer test of Curtiss V-1570 and D-12 engines, endurance test and flight tests of D-12 engine and a dynamometer test of a high compression-ratio D-12 engine. The engines and cooling systems used, the results obtained and troubles experienced are given in detail, with curves, sketches and views of the airplanes.</div> <div class="htmlview paragraph">Extremely low fuel-consumption was obtained, and the results show that the ratio of installed weight to power of a liquid-cooled airplane-engine is considerably reduced by using this system of cooling.</div>