KETTLE PROCESS 53 



gas is more quickly accomplished. This being done the brine 

 is allowed to stand from 20 to 24 hours, when the dirty yel- 

 lowish color, which is soon visible after the addition of the 

 lime milk, has disappeared, and a clear, slightly blue color 

 takes its place. Thus prepared the brine is ready for the 

 manufacture of salt. This process is called the settling of 

 the brine. The manufacture proper of salt is commenced 

 by lighting the fires under the kettles and rilling them 

 partly with brine from the faucets as soon as they become 

 warm, and within 3 to 4 inches of the top when evaporation 

 has well commenced. At the same time a wrought iron 

 pan is inserted into the kettle, having its handle near the 

 center instead of on the side to allow its easy insertion and 

 withdrawal from the kettle. Otherwise it is like an ordi- 

 nary frying pan, with very slanting sides, so that when it is 

 inserted into the kettle it covers its bottom and fits as close 

 as possible to the sides. This is known as the " bittern 

 pan." Its purpose is to collect the sulphate of lime, "plas- 

 ter " or " bitterns," which soon separates. This separation be- 

 comes more rapid with the increase of temperature and con- 

 centration especially near the boiling and saturation point 

 of the brine. From the time the pan is first inserted till the 

 brine actually boils or salt commences to separate, it is sev- 

 eral times drawn out of the kettle and the sediment collected 

 therein (the " plaster or bitterns ") is thrown into the gutter 

 beside the walk. That portion of the brine contained in the 

 kettle which is nearest to its bottom and consequently 

 becomes more strongly heated and therefore specifically 

 lighter ascends along the inner side of the kettle. When it 

 reaches the surface it is cooled by the cold air, becomes 

 again specifically heavier and sinks back to the bottom of 

 the kettle, but this time through the center, carrying with it 

 into the pan the separated and finely divided calcium sul- 

 phate. When salt commences to separate the pan is with- 

 drawn and the evaporation is allowed to go on undisturbed 

 till a sufficient amount of salt has separated, when the con- 



