Some useful results were obtained with compressed air used in crank engines; it is to be regretted that with this, also, apologies have to be made for the imperfect design and construction; they were old steam engines, some of those of two horse power losing from 25 to 30 per cent. by their own friction; some of the others tried, however, were far better, a newer type losing only from 8 to 10 per cent., while the 80 horse power referred to below showed an efficiency of 91 per cent. From these trials Prof. Riedler deduces--assuming 85 per cent. efficiency--a consumption of 611, 752, and 720 cubic feet per brake horse power. It is very evident from the foregoing that the Compressed Air Company, of Paris, will never do itself justice until as much thought and care has been devoted to the economical use of the motive power as has been expended in the means of producing it, and Professor Riedler's recent investigations should be especially useful in this respect. The question has indeed attracted the attention of more than one manufacturer, and reference is made to a particular type of small rotary motors which are being constructed by MM. Riedinger & Co., and which is stated have given very excellent results. These engines were specially used for working sewing machines and developed on the brake an efficiency of 34.07 and 51.63 foot pounds per second. Trials were made with a half horse power variable expansion Riedinger engine. TRIALS OF A SMALL ROTARY RIEDINGER ENGINE. ______________________________________________________________ | | Number of trials. | I. | II. ______________________________________________|_______|_______ | | Initial air pressure. lb. per square inch | 86 | 71.8 " temperature. deg. Cent. | +12 | +170 Ft. pounds per second measured on the brake. | 51.63 | 34.07 Revolutions per minute. | 384 | 300 Consumption of air for one horse power per | | hour. | 1,377 | 988 ______________________________________________|_______|_______