332 SAI/TING THE BUTTER 



the brine. The slow evaporation at a relatively high heat 

 causes the salt crystals to be relatively large and flaky, the 

 individual crystals appear to have rhomboid shape, they gather 

 into 'clusters forming large crystals, of the shape of hollow 

 pyramids. 



In the Vacuum Process the brine is conveyed from the 

 storage tanks to large heating tanks, where its temperature is 

 raised so that as soon as it enters the vacuum pan evaporation 

 commences. In the vacuum pans, which are huge iron retorts, 

 the brine is evaporated at relatively low temperatures under 

 reduced pressure. The evaporation is very rapid. From the 

 vacuum pan the crystals are conveyed to centrifuges, where 

 they are freed from about 95 per cent of their water. From 

 here on the process of drying and sifting is similar to that of 

 the Grainer process. In the vacuum process in some factories 

 mineral impurities are removed, in part at least, through a dis- 

 charge chamber in the bottom of the pan in which the "bitter 

 water," being heavier than brine and remaining in solution 

 longer, collects. The crystals produced by this process, as the 

 result of rapid evaporation at low temperature, are cube shape, 

 they are very small and remarkably uniform in size. 



In the Ahlsberg Process the brine is pumped through heat- 

 ers where it is subjected to very high temperature (about 280 F.) 

 under pressure. These heaters resemble water-tube boilers, the 

 brine flowing through the tubes and the spaces between the 

 tubes being charged with steam. In these heaters the brine 

 deposites its gypsum and other impurities forming a coating 

 on the tubes, which is daily removed by steel drills. From 

 these heaters the brine passes through gravel filters which 

 furnish an additional means to deposit the gypsum. From 

 here the brine enters large circular evaporating vats. As soon 

 as its pressure is released and the brine passes into these vats, 

 crystallization sets in. From these crystallizing vats the wet 

 salt passes through centrifuges for the removal of the bulk of 

 the water, and the dryers and sieves as described in the Grainer 

 and Vacuum process. The Ahlsberg process is particularly 

 adapted for salines whose brine supply contains considerable 

 mineral impurities, such as gypsum and which it is capable 



