18 THE CUBA REVIEW 



given place to the modern train of mills, sometimes consisting of as many as six 

 mills composed of 18 rolls preceded by one or two sets of crushers. To the crushers 

 the cane is brought by carriers, and the bagasse as it proceeds to the last mills is 

 treated with water and a combination of water and juice, so that the greatest possible 

 percentage of the sugar content may be extracted. From this point the juice no 

 longer goes to the old open kettle, but is carried to tanks in which it is treated with 

 milk of lime, in order to destroy its acidity and coagulate certain albuminous impu- 

 rities, this preventing the sucrose contained therein from reverting to glucose, and 

 thus being lost to the factory. From these tanks the juice proceeds to preheaters, 

 where it is heated to a temperature of about 215 Fahrenheit. From here the juice is 

 run into large settling pans where the solid and coagulated impurities sink to the 

 bottom and other substances float to the surface forming a scum. After this juice has 

 settled for a short time the clear juice is drawn off, and the settlings and scum and a 

 small portion of cloudy liquid are left in the tank. These are drawn off into other 

 tanks where they are further treated with lime, and then passed through filters under 

 heavy pressure, the clear juice coming from these being added to the clear juice 

 drawn off from the settling tanks. 



This now is conducted to the "effects". In the old system of boiling in open 

 kettles, it was very difficult to prevent the burning of the sugar after the syrup had 

 evaporated to a certain point, and furthermore the consumption of fuel was great. 

 It is well known that water will boil at lower temperatures on the top of a high 

 mountain than at sea level, that is, that the lower the atmospheric pressure on water 

 the lower the temperature required to cause it to boil or evaporate. This prin- 

 ciple has been taken advantage of in the sugar industry by the introduction of 

 "effects", composed of from three to six vessels, each receiving the vapor produced 

 by the evaporation of a liquid in the preceding vessel, and the air pressure in each 

 being less than that in the preceding vessel, these partial vacuums being produced by 

 means of air or "vacuum pumps". The lower portion of these vessels is porvided with 

 a system of copper tubes spaced at regular intervals, the whole being called a calandria, 

 and either live or exhaust steam is permitted to enter into the calandria of the first 

 vessel, thus causing the clear juice which is brought in from the settling tanks and 

 filter presses to boil and partially evaporate. The vapor thus produced is conducted 

 into the calandria of the second vessel, into which is introduced the partially evap- 

 orated liquid from the first vessel, and a portion of the air is extracted, thus causing 

 the heat in the vapor in the calandria to boil and further evaporate the liquid con- 

 tained in the vessel, this process being continued until the last vessel is reached 

 where a vacuum of about 26 inches is required, and where the final boiling tempera- 

 ture is brought down to about 150 degrees Fahrenheit, and in which the juice is boiled 

 down to a syrup containing about 35^ of water and 65 r 'r of solid material. It is 

 thus seen that the heat contained in the steam introduced into the calandria of the 

 first vessel, and for the production of which consumption of fuel was required, pro- 

 vides the necessary heat for the evaporation of the juice to the consistency just men- 

 tioned, and that thus a great saving in fuel is effected over that that would be required 

 were each vessel boiled direct, as was required in the old open kettle system. 



From the last effect the syrup is now pumped into the receiving tanks for the 

 vacuum pans. In these a vacuum of from 25 to 27 inches is maintained, in order to 

 reduce the quantity of steam required for boiling and remove the possibility of the 

 burning of the sugar as it is formed. At regular intervals from the top to the bot- 

 tom of the vacuum pans there are series of copper coils connected with a steam line 

 at one end and a drainage line at the other. As the syrup is drawn into the pans, 

 steam is allowed to enter into the coils, and as evaporation takes place, small grains 

 of sugar begin to form in the syrup. It is now the duty of the operator to cause 

 these grains to become larger, but to limit the number of grains that are formed, and 

 by proper manipulation of the contents of the pans and additions of fresh syrup at 



