ON METHODS OF DETERMINING THE DRYNESS OF STEAM. 397 



and {l—x)iu lb. of water at the steam temperature. Let W be the weight 

 of water initially in the condenser plus the equivalent reckoned as -vyater 

 of the condenser itself. Let t be the temperature of the steam, and i and 

 /tlie initial and final temperatures of the condenser water. Then 



xw {UlQ-0-7lt) + w{t-f)=W(f-i) 

 JN{f-i)-w(t-f) 

 i<'(1116-0-710 



To arrive at satisfactory results the temperatures must be read to ^V degree 

 at least, and the weight of steam condensed determined very accurately. 

 Further, it is desirable that the temperature i should be about as much 

 below the temperature of the place where the test is made as the tempera- 

 ture / is above it. A correction is easily made for the small fall of 

 temperature by radiation during the time the agitator is used to secure 

 uniformity of temperature. Suppose the agitator is used for two minutes, 

 and the temperature/ then noted. The temperature is again noted two 

 minutes later. The small observed fall is the loss in the interval by 

 radiation, and is added to the observed temperature /as a correction. In 

 the Mulhouse experiments the initial and final temperatures of the con- 

 denser were generally about 60° and 110° F. The following table gives 

 the results of the Mulhouse tests in 1859. They wore made very carefully, 

 and Him himself directed the tests. 



The committee at Mulhouse, in discussing the.se results, point out 

 their variability, and remark that a mean of numerous observations 

 should be taken. This is probably true when the test is made on a 

 small scale. In Mr. Willans's tests one hundredweight of steam was 

 condensed in each test, and this gives what is virtually a mean of 

 numerous smaller tests. In the case of Trial 23, the Mulhouse Committee 

 thought that the calorimeter underestimated the amount of priming 

 water. 



About 1860, Joule used a calorimeter veiy similar to the above, in 

 order to determine the total heat of steam and verify Regnault's results. 

 The paper describing the experiments ' is interesting as showing that 

 fairly accurate results can be obtained by this method, used on a small 

 scale, when the observer is sufficiently skilful. The amount of steam 

 condensed was only from 8,700 to 14,100 grains in each test. Tem- 

 peratures were read to three decimal places. The weight of water in the 

 condenser was about 140,000 grains. The steam flowed into the con- 

 denser for two minutes. The steam must have been almost perfectly dry, 

 as the following (mean) results show : — 



The method has been often used in determining the wetness of steam 

 in boiler trials, but very often the arrangements have been so rough 

 that no reliance can be placed on the results. A calorimeter of this 



'■ ' The Scicnttfc Papers of J. P. Joule, vol. i. p. 482. 



