SAI/TING THE BUTTER 331 



ty, in some localities the wells yield a brine of a relatively high 

 degree of chemical purity, while in other localities the admixture 

 of undesirable minerals and mineral salts, such as gypsum and 

 magnesium chloride, iron, etc. is very marked. For this reason 

 there is a wide difference in the need of purifying processes 

 used in the different salines, in order to attain purity. 



The brine from which the butter salt is manufactured in 

 this country is secured from wells which reach salt deposits 

 which lie anywhere from 1500 to 3000 feet below the surface. 

 When the salt stratum is to be penetrated a double pipe is put 

 down. The outer one, which represents the diameter of the well, 

 about 6| inches, reaches the top of the salt bed, while the inner 

 tube which measures from 3J to 4| inches in diameter, goes clear 

 through to the bottom of the salt deposit. Fresh water is 

 pumped down the outer tube. This dissolves the rock salt, and 

 the brine thus formed under continued pressure, rises to the 

 surface through the inner tube and is conveyed to large tanks, 

 the settling tanks, where it is allowed to settle and clarify. 

 From this point on the brine is passed through one of three 

 processes, the grainer process, the vacuum process, or the Ahls- 

 berg process. These processes largely determine the degree of 

 purity of the salt and the shape of the salt crystals. 



The Grainer Process is the oldest process. It simply con- 

 sists of pumping the brine from the storage or settling tanks 

 into large evaporating vats equipped with steam coils which are 

 charged with exhaust steam. In these vats the brine is heated 

 to the boiling point under atmospheric pressure. As the water 

 evaporates, crystals form on the surface where evaporation is 

 most rapid. These crystals unite into larger aggregates, which 

 gradually drop to the bottom and are drawn out of these vats 

 by mechanical, slowly-moving rakes. These salt crystals are 

 piled on a platform where they are allowed to drain or they 

 are centrifuged to remove the bulk of the water and are then 

 subsequently dried and run through sieves. No attempt is made 

 in this process to purify the brine from mineral impurities, 

 except possibly to bleach it by addition of small quantities of 

 lime. The chemical purity of the salt made from this brine 

 will therefore almost wholly depend on the natural purity of 



