CANE SUGAE. 



Per square foot of heating surface per hour a quadruple will receive 

 normally 1600 B T.U. ; the first vessel then utilizes 1600 17 = 1583 

 B.T.U. ; the second vessel receives 1583 B.T.U., and utilizes 1583 16 = 

 1567 B.T.U. ; similarly the third and fourth vessels utilize 1554 B.T.TJ. and 

 1548 B.T.U. 



The useful effect then is 6252 B.T.U. and not 6400 B.T.U. ; that is to 

 eay, when in a non-radiating non-conducting quadruple a pound of steam will 

 evaporate four pounds of water, in a naked wrought-iron quadruple it will 

 evaporate 3-906 pounds; this loss will however be recoverable at quadruple 

 effect, so that for every four pounds of water evaporated '023 lb, steam, or say 

 22 B.T.U. are to be made up ; in a factory evaporating 60,000 Ibs. water per 

 hour the B.T.U. to be made up will 

 then be 330,000. In Chapter XIX. 

 a pound of megass is estimated as 

 affording for factory purpose 2922 

 B.T.U., so that the loss per hour in 

 radiation from a 10,000 square foot 

 naked standard evaporator is of the 

 order 113 Ibs. of megass or 2712 Ibs. 

 per day. 



It is not unusual to see evapora- 

 tors only protected in part ; what is 

 the actual loss is almost impossible 

 to say ; this calculation shows, how- 

 ever, that the loss is quite appreciable 

 and well worth saving. 



FIG. 180. 



Utilization of Vapours 

 from the last Body. A not 



negligible economy of heat may be 



obtained by using the vapours from 



the last body to heat cold juices ; the 



temperature to which the juice can 



be heated depends, of course, on the 



degree of vacuum in the last body; a 25 inch vacuum corresponds to a 



temperature 133F., and with that vacuum this is the highest temperature to 



which the juice can be raised. A numerical example will make the economy 



of this scheme clear. 



Let there be evaporated under a 25 inch vacuum in the last body of 

 a multiple effect 233 Ibs. water per 1000 Ibs. of juice; the condensation of this 

 quantity of vapour will afford 238,126 B.T.U. Now, taking the specific heat 

 of juice as 0-9 and the initial temperature as 84 F., to raise 1000 Ibs. from 

 84 F. to 133 F. requires 44,100 B.T.U., so that 18'5 per cent, of the vapour 



324 



