CANE SUGAR. 



The inefficient working of a kiln may arise from the following 

 points : 



1. Scaffolding, which may as already mentioned be caused by the presence 

 of silica or alumina, and also by careless work in changing or in mixing the 

 limestone and fuel. 



2. "Withdrawal of unburnt lime when too little fuel is used or when com- 

 bustion is too rapid. 



3. Presence of carbon monoxide, due to too little air being admitted for 

 complete combustion, or to a too low temperature in the kiln. 



4. Presence of air due to leaks in the masonry or to air sucking back, or 

 to working the pump too fast. 



The composition of the gas from the kilns varies within wide limits, the 

 theoretical maximum of carbon dioxide being 38- 7 per cent. ; in general 

 practice the percentage lies between 25 per cent, and 30 per cent., with from 

 1 per cent, to 3 per cent, of oxygen and 65 per cent, to 70 per cent, of 

 nitrogen. Traces of carbon monoxide may be present but should not rise 

 above 1 per cent. ; sulphur dioxide derived from sulphur in the coal may also 

 occur. 



Carbonic Acid Gas Pumps. The pumps used to aspirate the 

 carbon dioxide are now slide valve pumps similar in design and construction to 

 those used in the dry vacuum process described in the Chapter on Evaporation. 

 A table of their capacities is given below, taken from a Continental maker's 

 catalogue. 



270 



