four chapters, and here I have had the advantage of the remarks and valuable criticism of Professor Capper, of King's College, London, who also kindly made for publication in this work a new test upon the experimental OttoCrossley gas engine in the engineering laboratory of King's College-a test which is, perhaps, as complete as any that have been published. Chapter XVII., on the "Chemical Composition of Gas"—an important part of the subject— has been entrusted to Mr. G. H. Huntly, A.R.C.S. of the State Medicine Laboratory, King's College, who is responsible for this chapter only. Care has been taken to consult the best authorities in England and on the Continent who have written on the theory and practice of gas engines, and to bring the matter up to date. I have much pleasure in acknowledging my special obligations under this head to M. DelamareDeboutteville of Rouen, and Professor Schröter of Munich, for their kind assistance. To Professor Kennedy, F.R.S., also, who has made many exhaustive and reliable tests on English gas engines, my acknowledgments are due. Not much original work appears to have been done in the United States, but the subject has been thoroughly studied in France and Germany. An Appendix is added, in five Sections, containing information which it was not found possible to incorporate in the text. One of them gives an abstract of the valuable experiments recently made by Dr. Slaby of Berlin, and published after the main portion of this work was complete. In conclusion, there only remains for me to emphasize the fact of the constantly increasing use of these motors in all countries for industrial purposes. Undoubtedly, there is a great future before them. There still exists, however, a large field for economy. In both Oil and Gas Engines, about 40 per cent. of all the heat received now goes off in the exhaust gases, and about 35 per cent. in the jacket water. The better the economic results obtained, the greater will be the demand for these convenient motors. At present their chief recommendation is the absence of a boiler, which is of great advantage, especially for small powers. Even with the very high temperatures in the cylinders there is also little or no difficulty with lubrication. They are yearly increasing in size and power,* and will certainly before long, as more knowledge and experience are brought to bear on their construction, enter into formidable competition with the best steam engines. They may even constitute the principal heat motors of the future. A list has been added of the chief tests on Gas, Oil, and Air Engines that have been published up to date. BRYAN DONKIN, JR LONDON, November, 1893. *On going to press a notice of a Three-Cylinder Horizontal Doubleacting Compound Gas Engine, indicating 600 to 700 H.P., is given in The Engineer of November 10, 1893. |