Till! THKH.MODYNAMICAI, PROPERTIES OF SUPKRHKA'IT.I> >l KAM. 19 



pass,-.! with tlie water from the steam chest, the temperature of the wiredrawn steam 

 l>ecame lower by nearly 0'3 5 in about 10 minutes, and remained at this lower value 

 v Ion.,' as the drainage was thus restricted. This decrease of temperature was 

 clearly noticeable, and, though its amount was relatively small compared with the 

 increase of wetness in the steam in the steam chest, its existence seemed to impair in 

 a slight degree the deduction that the condition of the steam was always the same 

 just before entering the orifice. 



There is, however, one point to notice which has not previously been mentioned, 

 and which was suggested to the author by Professor REYNOLDS as accounting for this 

 peculiar difference observed in the temperature of the wiredrawn steam ; the water 

 in the boiler is certainly not free from air, and even a small quantity of air hi the 

 steam entering the steam pipe with the steam, owing to the fact that a large quantity 

 of steam leaving the l>oiler is condensed in the pipe and steam chest, would, if the 

 actual steam drained away is very small, represent a much greater percentage of air 

 entering the orifice with the steam than in the steam leaving the boiler. With good 

 drainage of steam and water from the steam chest, this percentage of air would l>e 

 very much smaller and most of it would be carried away through the drain pipe on 

 account of its slightly greater density. 



In any case, however, this maximum difference of temperature in the wiredrawn 

 steam is scarcely sufficient, considering the good drainage usually allowed from the 

 steam chest in the experiments and the general accuracy to which the results 

 attained, to justify the conclusion that the conditions of the steam just before passing 

 the orifice was ever materially altered. 



An examination of all the results of experiments with steam of different conditions 

 of wetness in the steam chest certainly shows that by withdrawing steam upwards 

 from a steam chest containing wet steam, and allowing the moisture to separate by 

 gravitation, the steam can always be obtained in the same condition as to dryuess, 

 and it is to these results that the author looks for experimental justification for 

 taking the total heat of the steam before entering the orifice, to be given by tables 

 deduced from the results of REONAULT'S experiments on the total heat of evapora- 

 tion of saturated steam. 



SECTION XII. On the Energy of Motion of the Steam at places where the 

 Temperatures and Pressure* are obscmed. 



Among the many causes which influence the results of experiments on the wire- 

 drawing of steam, the energy of motion of the fluid at the places at which the 

 temperatures and pressures are taken is perhaps the chief. As will be seen in the 

 figure, the thenno-juuction by which the temperature of the wiredrawn steam is 

 ascertained, is about 'J inches from tin; orifice in a narrow channel, and it is to these 

 tempi-rat mv readings that we must look for the maximum effect of this energy of 



D 2 



