326 



CHAPTER XVIII 



for use, since the water here, being usually under pressure, discharges 

 itself. 



The writer examined a number of apparatus to obtain information on 

 this matter : the detailed results obtained with one vertical submerged 

 tube apparatus are given in the two schedules below ; these differ in no essen- 

 tial from other results obtained in other apparatus. In these experiments 

 the rate of evaporation was obtained by observing the time required to fill 

 a tank holding 39,100 Ibs. water with the discharge from the first cell : this 

 observation is recorded as T in seconds. The apparatus had 14,146 sq. ft. 

 heating surface, calculated on the inside of the tubes and including the tube 

 plates and circulating well. The coefficients of transmission in the first and 

 fourth cell and the coefficient of the apparatus as a whole are recorded in 

 B.T.U. per i F. per I sq. ft. per I hour as k v k and k m ; per Ib. of water 

 evaporated a flat rate of 1,000 B.T.U. is taken for each cell ; an equal 

 evaporation is taken as obtaining in each cell, as was found experimentally 

 to be very nearly the case. The ratio of steam condensed to water evaporated 

 is taken as I : 4 ; actually 1:4-3 was found for the whole apparatus, but this 

 quantity was not determined for each cell. 



The experiments were all made over one day so as to remove as far as 

 possible errors due to scale formation, and when the conditions were altered 

 a sufficient interval was allowed to enable the apparatus to adjust itself 

 to the change. 



RATE OF EVAPORATION IN A QUADRUPLE EFFECT AS INFLUENCED BY 



IN LAST BODY. 



VACUUM 



Another series in the same apparatus, but the converse of the above, 

 namely, keeping the cold end constant and increasing the temperatme of 

 the heating steam, gave the following results : 



