THE EVAPORATION OF THE JUICE TO SYRUP. 



interposed in the vapour pipe connecting any two bodies, and is placed in 

 either a horizontal or vertical position ; placed in the vessel are perforated 

 diaphragms, generally three in number, the sum area of the perforations 

 being greater than the area of the vapour pipe ; the diaphragms are sometimes 

 dispensed with. Horsin Deon 6 states that as the most appropriate dimensions 

 the Ralentisseur should be 3-5 times the diameter of the vapour pipe, and that 

 the length should be twice the diameter. 



The action of this apparatus is two-fold ; the sudden increase in area of 

 the pipe decreases the pressure of the vapour, so that the external pressure on 

 the bubble is diminished and the latter bursts ; in addition, there is the effect 

 of the shock the bubbles suffer on striking on the walls of the diaphragms. 



A sudden change in direction has also been observed to diminish entrain- 

 ment losses, and vapour pipes are sometimes supplied with an enlarged section 

 in which the direction of the vapour is twice abruptly changed by means of 

 baffle plates. 



A second form of entrainment preventer, the patent of Messrs. John 

 McNeil & Co., is shown in Fig. 177. Within the dome-shaped cover a of the 



FIG. 177. 



effect or pan is arranged a conical vessel 1. The orifice of this funnel is- 

 pointed in the direction opposite to the pipe leading to the next effect or to 

 the condenser. Particles of juice are projected on to the roof and thence fall 

 on to the sides of the cone, and the vapour in its passage round the cone also 

 deposits particles of liquid. The condenser pipe c projects inwards to prevent 

 these particles from being swept forward with the current of vapour. 



In the factories with which the writer has been connected entrainment 

 losses were so small that it was practically impossible to estimate them, and 

 it was only in waste water from the last vessel of the evaporator that sugar 

 could be detected, and then not by any means always. 



Fries 7 in Hawaii ingeniously placed small pipes in the vapour pipes of 

 the effects and pans and measured the sugar there collected over definite 

 periods ; he found a loss of -006 per cent, in the pans, and a variable loss of 

 002 per cent, to -008 per cent, in the evaporators. 



307 



