1 62 THE SCIENTIFIC PAPERS OF 



had been put to work in Paris, and had been examined by 



G-en. Morin and M. Tresca, and in a whole day's working the 



consumption of coal had been found to be 1/67 kilos, or 3'68 Ibs. 



per break horse power per hour. But on attempting to carry out 



the same plan in engines of larger size, of 20 horse power or more, 



difficulties had arisen in every direction, which had compelled 



him to relinquish the endeavour. One difficulty had been that 



mentioned in the paper with regard to the joints ; and he had 



found that the best joint to resist a high heat was made by turning 



a number of concentric grooves in the faces of the flanges, and 



filling them with a cement composed of fine dust of cast iron 



mixed with white and red lead previously mixed up with linseed 



oil, and worked into a very stiff cement that set as hard as iron 



when exposed to heat ; by that means he had succeeded in making 



tight joints. But what had discouraged him at that time was the 



result he had arrived at in preparing a paper * to which reference 



had been made, " On the conversion of heat into mechanical 



effect." In considering what would give a proper conception of a 



really perfect engine, he came to the conclusion that if steam were 



generated at such a pressure as to occupy only the same bulk as 



the water itself, and were then expanded down until it was all 



condensed through expansion, the utmost effect theoretically 



possible would thereby be obtained, because the whole of the heat 



would have been converted into mechanical effect. In Fig. 2, Plato 



32, the diagram of a portion of the dynamical expansion curve of 



steam, the shaded rectangle showed the utmost power that could 



be obtained in a condensing engine with perfect vacuum using 



* (See Proceedings of the Institution of Civil Engineers, 1852-53, p. 571). 

 In the Steam expansion curve shown in Fig. 2, Plate 32, the horizontal scale 

 gives the volumes of steam compared with the volume of the water from which 

 it is produced ; this is the correct dynamical expansion curve of saturated st' am 

 allowing for the loss of the heat that is converted into mechanical effect when 

 the steam is expanded behind a working piston ; the shaded area, or any other 

 rectangle drawn to the curve, represents the power obtained from a condensing 

 engine with perfect vacuum but without expansion. In the Air expansion curve 

 shown in Fig. 1, Plate 31, the horizontal scale gives the volumes of air compared 

 with the volume of an equal weight of water ; the dotted curve is the hyperbolic 

 expansion curve of constant heat, representing Marriotte's law that the pres&ure 

 and volume are inversely proportionate to each other ; and the full curve represents 

 the actual rate of expansion, showing the reduction of temperature during expan- 

 sion, and the consequent contraction of volume ; this curve is in accordance with 

 the observed fact that, when air at any pressure and at the temperature of 32 

 Fahr. is compressed to double its original pressure, its temperature is raised 70 

 Fahr. 



