392 REPORT— 1894. 



Methods of Detcrminiiuj iho Dri/ness of Steam. — Report of the Com- 

 mittee, consistinij of Sir F. J. Bramwell, Bart. (Chairman), 

 Professor T. H. Beare, Mr. Jeremiah Head, Professor A. B. W. 

 Kennedy, Professor Osborne Reynolds, Mr. Mair Rumley, Mr. 

 C. I. Wilson, and Professor W. C. Unvvin (Secretari/). 



The determination of the quality of steam, or its wetness, has come to be 

 of very great importance both in boiler trials and engine trials. It was 

 in the classical researches of G. A. Hirn at Logelbach in Alsace in 

 1854-57, and in subsequent experiments by MM. Grostete, Hallauer, and 

 Leloutre, and other members of the Societe Industrielle of Mulhouse, 

 that the great importance of the action of water in the steam-engine 

 cylinder was fii-st clearly recognised. It was perceived that the water 

 present in the cylinder, and which may amount to 50 per cent, of the 

 steam introduced, was due to three distinct causes : (a) initial wetness 

 of the steam ; (b) condensation in the mass of steam due to adiabatic 

 expansion ; (c) the action of the cylinder wall. An accurate discussion of 

 the results of an engine test is impossible if the initial condition of the 

 steam is unknown, both because the total heat per pound of steam 

 received by the engine depends on its dryness, and because water 

 introduced with the steam increases the prejudicial action of the cylinder 

 wall. 



In boiler tests the evaporative efficiency is measured in pounds of 

 water converted into steam per pound of coal. But if part of the feed 

 water supplied leaves the boiler as water entrained in the steam, the real 

 evaporation is less than the apparent evaporation. The entrained water 

 must be allowed for in estimating the evaporative efficiency of the boiler. 

 Further, a boiler which supplies wet steam is a bad boiler, because wet 

 steam is prejudicial to the efficiency of the engine, and it should be one 

 object of a boiler trial to determine whether the steam is of good quality. 



The earliest attempts to detenuine the amount of moisture in steam 

 which have come to our knowledge were made during some boiler trials 

 by a committee of the Societe Industrielle of Mulhouse.' This committee 

 tried three methods : 1. A Method of Separation. — The whole of the steam 

 was taken through a spare boiler, without fire, in the expectation that the 

 moisture would be deposited. The increase of water in the spare boiler 

 during a trial was measured, and that part of the increase due to con- 

 densation by radiation was determined by a special experiment. 2. A 

 Condensing Method suggested by Him. — Some of the steam from a boiler 

 under trial was condensed and its total heat determined. By comparing 

 the total heat per pound with that of dry saturated steam the amount of 

 moisture was ascertained. 3. A Chemical Method. — Salt was introduced 

 into the boiler, and the diminution of saltness of the boiler water during 

 a test determined. It was assumed that moisture in the steam would be 

 of the same saltness as the boiler water, and therefore the amount of salt 

 removed measured the wetness of the steam. In these early trials only 

 the second method appeared to give reasonable results. But the com- 

 mittee did not place full reliance on any of the methods tried. 



Origin of the Water Suspended or Entrained in Steam. — There are 

 three sources of the water found in steam : — 



" ' Report of MM. E. Burnat and E. Dubied,' Bidletm do la Societe Industrielle de 

 Mulhouse, 1859. 



