106 MANUAL FOR SUGAR GROWERS. 



A certain amount of skill is required to adjust the 

 conditions during the concentration, that the crystals 

 may be properly formed, and in this the art of the 

 pan-boiler consists. 



The following is an outline of the method of work- 

 ing : The air-pump is first started so as to create 

 a vacuum in the pan ; the cock connected with the 

 syrup or feed-pipe is next opened, and syrup drawn 

 into the pan in sufficient quantity to cover the 

 lower steam coils ; steam is turned on, and the syrup 

 rapidly boils down. Fresh syrup is drawn in, in 

 small quantities, from time to time, until the boiling 

 mass begins to show signs of crystallising or grain- 

 ing. When this takes place the successive charges 

 of syrup are admitted with care, so as to build up 

 the grain slowly. Larger quantities of syrup being 

 admitted at a time, as the pan becomes filled, and 

 steam being turned on in the successive coils as the 

 syrup covers them, the progress of the operation 

 can be watched through sight-glasses let into the 

 upper part of the pan. Small quantities of syrup 

 can be withdrawn for inspection by means of an ap- 

 paratus known as a proof -stick, an ingenious piece 

 of apparatus fitted to every vacuum pan. 



Attached to the pan are thermometers, by means 

 of which the temperature of the contents of the pan 

 can be ascertained. Vacuum gauges are also at- 

 tached, which show the extent to which the pan is 

 exhausted of air and vapour. The vacuum gauge 

 indicates " inches of vacuum," or the height in 

 inches to which a column of mercury would rise in 

 a tube one end of which was connected with the 



