APPENDIX B. 187 



above the bottom, the flow of the brine being controlled by gates. 

 The supply pipes from the cisterns are usually made of wooden 

 pump logs having a 3-inch bore. 



The brine, as shown by the analyses, contains a small percentage 

 of carbonate of protoxide of iron, held in solution by an excess of 

 carbonic acid. 



If. the brine was boiled down or evaporated with this iron in, it 

 would give the salt a red color and very materially affect its commer- 

 cial value. 



As soon as the cistern is filled with brine, preparation should 

 be made to settle it. A tight box large enough to hold a barrel or 

 more of water is placed on the top of the cistern. In this a proper 

 quantity of fresh burnt lime is slacked with fresh water, enough 

 being afterward added to fill the box, so as to make a whitewash 

 or milk of lime. This mixture being a caustic lime, is freely sprinkled 

 over the brine. The brine is then thoroughly "plunged" — that is, 

 it is stirred up until the lime is well mixed with the brine. The 

 caustic mixture of lime having a strong affinity for the carbonic 

 acid extracts the same from the brine, thus releasing the iron which 

 is precipitated with the lime to the bottom of the cistern as an 

 insoluble peroxide of iron. The brine is then allowed to rest for 

 48 hours, when it is quite clear and ready for the boiling house 

 or block. This process is called "settling," and on the care with 

 which it is conducted depends much of the success in making good 

 salt. 



EVAPORATION OF BRINE. 



Having made a stock of settled brine, the next process in the 

 manufacture of salt is the evaporation of the brine ; and this is ef- 

 fected by three different methods : 



1st. By the direct application of fire-heat to kettles and pans. 



2d. By the use of steam, either exhaust steam from saw-mills, 

 or steam generated by flue boilers built expressly for the pur- 

 pose. 



3d. By solar evaporation. 



EVAPORATION OF BRINE IN KETTLE BLOCKS. 



A kettle block for evaporation of brine consists of a wooden build- 

 ing, 140 feet long by 45 to 50 feet wide, with an elevation of 18 



