MINERAL RESOURCES OF THE STATE OF NEW YORK 23I 



•Grainers are now employed in practically all of the plants engaged 

 in making salt for domestic uses. They are seldom used .alone, 

 but most often in conjunction with open pans or with vacuum pans. 

 The grainer consists of an open vat, loo feet or more long, 12 to 15 

 feet wide, and about 2 feet deep, built of iron alone or lined with 

 concrete or wood with a series of iron pipes, running the length of 

 the vat and placed about a foot from the bottom, in which the steam 

 is supplied. The brine is preheated outside of the grainer by waste 

 steam. The process of -salt making employs the principle of factional 

 crystallization, whereby the concentration of the brine is kept above 

 the point of saturation for the more soluble chlorides of -magnesium 

 and calcium; as the bittern becomes charged with these it is drawn 

 off and wasted or employed in a second series of grainers for making 

 an inferior grade of salt. The salt particles ir.om the grainer are 

 often composed of several small crystals, giving. a coarser size than 

 with the open pan. The salt is removed by m.echanical rakers which 

 operate continuously or by hand. Operations have to be suspended 

 at intervals to scale the walls and pipes, the period of evaporation 

 ranging from a few days to several weeks, depending on the amount 

 of calcium sulphate in the brine. 



Vacuum pans, technically, are superior to all other rmechanical 

 devices for evaporating salt, as they are most economical of heat and 

 require less attention in proportion to the quantity of product. 

 Their main drawback is the high cost of installation. As in use in 

 New York they consist of a vertical cyclinder, terminated at each 

 end by a cone, built of sheet iron or steel. The .steam for heating 

 is supplied to a belt within the middle or the cylindrical part of the 

 pan, in which is placed a series of copper tubes immersed in the brine 

 or through which the brine is pumped. Vacuum is maintained by 

 means of a pump connected with the top cone, assisted by rapid 

 condensation of the steam as it comes off at the same place. The 

 salt as it crystallizes falls to the bottom and is discharged through a 

 pipe, after which it is drained bj^ a centrifugal. A vacumn of about 

 28 inches is maintained in the pan, if operated as single effect. At 

 one plant there are four pans connected to work as a quadruple 

 effect, in v/hich the brine is maintained under a vacuum of about 

 13 inches for the first, 20 inches for the second, 26 inches for the 

 third and 28 inches for the fourth. Boiling takes place at progress- 

 ively lower t-emperatur-es with increase of vacuum. The :pans have 

 to be boiled out every day or so and scaled at intervals of a few 

 months. 



