MANUFACTURE OF SALT 67 



only a much heavier expense than the present price of ordi- 

 nary salt will warrant, but by their use we would substitute 

 sodium sulphate for calcium sulphate, which when present 

 in the salt would be more objectionable than the latter. 

 Moreover the decomposition of the calcium sulphate by 

 sodium carbonate or trisodium phosphate would involve at 

 the same time the decomposition of the calcium and mag- 

 nesium chlorides into calcium and magnesium carbonates or 

 phosphates, thus bringing the expense for these chemicals 

 up to such a high figure per bushel of salt that their use is 

 out of the question. 



The other impurities found in the salt brines of the State 

 of New York which have an important bearing on the man- 

 ufactured product are the very soluble and deliquescent cal- 

 cium and magnesium chlorides. Although only present in 

 the brines in small quantities, namely from about 0.15 to 

 0.75 per cent, they accumulate in the pickle or bitter water 

 as the salt is removed, no matter by what method we obtain 

 the salt. Thus in the solar salt fields they accumulate 

 (gradually) in the pickle to such an extent, as previously 

 stated, that evaporation practically ceases, when such a 

 pickle contains only about 8 per cent of salt but nearly 21 

 per cent of the chlorides. In properly attended salt works 

 the pickle is removed before such an accumulation of the 

 calcium and magnesium chlorides takes place. It is usually 

 discharged whenever it becomes necessary to scale the ket- 

 tles, pans or grainer pipes, though in some grainer works a 

 certain portion of the pickle is removed every two or three 

 days from the upper into the lower grainers. When a certain 

 ratio exists between the salt and these chlorides (especially 

 the magnesium chloride) in a pickle evaporated by artificial 

 heat a thin film is formed over the heated but not boiling 

 liquid, which greatly retards evaporation and forms again as 

 soon as removed. This is an indication that the chlorides 

 of the alkaline earths should be removed. 



