THE EVAPORATION OF THE JUICE TO SYRUP. 



elevated. Claassen 1 estimates that no practical benefit is obtained by in- 

 creasing the vacuum, in the last body above 60 cm. (= 23'7 ins.), as the 

 decrease in the coefficient of transmission is sufficient to neutralize the increase 

 in difference of temperatures. 



The effect of the velocity of the juice has been experimentally studied by 

 Porkong 2 , whose data are as follows : 



With a velocity of juice 1*29 metres per second, the calories transmitted 

 per minute and per square metre were, per 1C. difference in temperature, 

 8-15, and with velocities 1'Soand 1*523 the corresponding calories were 16*25 

 and 17-71. 



The coefficients of transmission under actual conditions have been studied 

 by Jelinek and by Claassen 3 . Their results are given below : 



Triple First vessel 37 calories. 



Second vessel 25 ,, 



Third vessel 14 



Quadruple First vessel 28 , , 



Second vessel 26 ,, 



Third vessel 20 



Fourth vessel 5-6 ,, 



Vacuum pan . . . . Graining 18 ,, 



Boiling .. .... . . 10 



Bringing up 3-7 ,, 



Vacuum pan for low products 6-7 ,, 



(Jelinek). 



Fore evaporator 50 calories. 



Quadruple First vessel 45 , , 



Second vessel 30 ,, 



Third vessel . . . . 20 



Fourth vessel 12 



Eeheating diffusion juices, carbonation juices and 



syrups 5 ,, 



Vacuum pan first products 10 ,, 



,, ,, low products 5 ,, 



(Claassen.) 



The calories here given are metric calories. The low transmission 

 coefficients found with heating juices as compared with those found with the 

 juices in the evaporator are due to the fact that in the latter case the juices 

 are actually boiling. 



Superheated Steam. Superheated steam is a much worse conductor 

 of heat than is saturated steam, and hence the loss of heat in steam pipes is 

 much less with superheated steam than with saturated ; in addition, super- 

 heated steam can be used more economically in the cylinder of an engine 



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