THK Till .I:MD])VN-\MICAL PROPERTIES OF SUPERHEATED STEAM. 9 



pipe and V 2 in the drain pipe, and its value is read by means of a pressure gauge, 

 the siphon from which, enters the channel CC at 8. The pressure p t in the steam 

 after passing the orifice is regulated by the valve V 8 ; but as the pressure below this 

 valve is the same as that in the air vessel below the condenser, by sufficiently 

 reducing this pressure in the air vessel by means of the air pump, it is possible to 

 maintain any value of p it ranging from 2 or 3 Ibs. absolute to /> the pressure in the 

 chest RR. 



The steam jacket to cover the channel containing the wiredrawn steam is 

 shown in fig. 4. It was constructed so as to completely surround the channel 

 leading from the orifice to a distance of about 8 inches from the orifice. 



The portion of the channel surrounded by the jacket is separated from the other 

 parts of the channel by the orifice plate O at one end, and by a ring of cork or 

 asbestos at the other end pp, fig. 3. It consists of two sections at right angles to 

 each other, a thermo-j unction t.,t., entering at the elbow, and the siphon of a pressure 

 u r .nige for registering the pressure />, entering at S^ 



The steam jacket is supported by the channel it surrounds, and is itself a complete 

 and enclosed vessel ; it was made of cast iron, its thickness $ inch throughout, and 

 was made in two halves, so that it could be removed, if required, without disturbing 

 the remainder of the apparatus. These two halves are bolted together, the joints 

 being made by rings of copper. The jacket steam was drawn from the pipe xx 

 (fig. 2) coming from the boiler, by the branch pipe yy, and a small flow of steam 

 was kept up through the drain pipe vv from the jacket. The temperature in the 

 jacket was regulated to any desired value by altering the pressure of the steam in 

 the jacket by the valves V 4 and V 6 in the admission pipe yy and drain pipe vv 

 respectively. 



The idea of constructing a steam cosie,* which should lie entirely independent 

 of the steam channel it surrounds, was due to Professor REYNOLDS, and the author 

 is indebted to Mr. FOSTER, the chief assistant in the laboratory, for valuable aid in 

 its construction. 



Such, then, is the apparatus as finally used in the experiments. Its arrange- 

 ment was, however, not altogether a simple matter of preconceived design, but was 

 the outcome of continued adaptability and enlargement to meet the necessities and 

 difficulties as they arose. 



The source of steam supply when initial pressures up to 50 Ibs. per square inch 

 were used was a large Lancashire boiler used for heating purposes. When higher 

 initial pressures were required, the author obtained permission from Professor 

 REYNOLDS to use the locomotive boiler used in connection with the experimental 

 engines in the Whitworth Engineering Laboratory of the Owens College, Manchester, 

 and the author must express his indebtedness to the assistant, Mr. J. HALL, for the 

 excellent manner in which the boiler pressure was kept constant during the long 



* Used by REONAULT in his latent heat experiments. 

 VOL. CXC1V. A. C 



