MANUFACTURE OF SALT 6 1 



4 VACUUM PAN EVAPORATION 



or the evaporation of water from brines by steam, with a re- 

 duction of atmospheric pressure over the heated brine has 

 been successfully introduced into two localities in this state, 

 namely at the Duncan Salt Company's works, Silver Springs, 

 Wyoming Co., and at Ludlowville, Tompkins Co. At the 

 former place the process is carried on under the Duncan 

 patents and at the latter under the Alexander Miller patents. 

 Their product is a very handsome salt with a fine luster and 

 very even grain, well adapted for table and dairy salt. The 

 following generalized description of the former is furnished 

 by Mr W. C. Clarke, E. M. 



The vacuum process consists in evaporating the brine in 

 a large vertical cylindrical iron vessel in which a vacuum is 

 produced. By withdrawing the atmospheric pressure the 

 boiling point of the brine is lowered whereby a quicker 

 crystallization is produced and consequently a finer grain. 

 In the pan are 17 or 1 8 groups of copper tubes, 20 tubes in 

 each, the latter being parallel to each other and in one 

 plane. At each end they are connected with an iron tube 

 or heading at right angles to the copper tubes and in the 

 same plane, through which steam from the outside connec- 

 tions is admitted to supply heat for evaporation. The copper 

 tubes are surrounded by brine. The salt as it crystallizes 

 collects in a large pipe at the bottom of the pan and when 

 it is seen through a peep hole in the latter a valve is closed 

 above the salt and it is dumped into a cylindrical screen 

 revolving at about 600 revolutions per minute. The water 

 is thrown against the screen and goes through by centrifugal 

 force. The salt when dry, is ready for packing. This is the 

 Worcester brand and a price much above that of the ordi- 

 nary grainer salt is obtained for it. 



COMPARISON OF BRINES AND PROCESSES 



As the brines used in the western part of the state — where 

 the pan and grainer methods are exclusively employed — 



