PURIFICATION OF SALT. 1 5 



The bicarbonate from Syracuse, New York, was of the following 

 composition, according to the report of the Solvay Process Company: 



Per cent. 



Silica 0.006 



Ferric oxide and alumina 002 



Calcic carbonate 030 



Magnesic carbonate 005 



Sodic chloride 070 



Sodic carbonate 5 22 



Sodic bicarbonate 99-300 



This material, already very pure for a commercial substance, was 

 easily further purified by repeated washing with cold water, which was 

 sufficient to remove most of the chloride. 



A portion of the Syracuse bicarbonate, thus washed four times with 

 cold water and thoroughly drained each time with a reverse platinum 

 filter, was nearly all dissolved in water. After settling, the result- 

 ing clear solution was decanted, neutralized with hydrochloric acid, 

 and then evaporated to dryness. The sodic chloride was fused in 

 platinum, dissolved, and considerably diluted. After long standing 

 the clear upper portion was decanted from very finely divided silica. 

 This method of fusion is a very effective means of separating silica, 

 but the precipitate is so fine as to require a long time to settle, and as 

 to run through most filtering septa. Hence cautious decanting, with 

 rejection of the considerable lower portion of the solution, is neces- 

 sary. The unimpeachable solution of salt thus obtained was concen- 

 trated and twice precipitated by hydrochloric gas (H), twice more 

 precipitated (I), and yet twice more precipitated (J). Analysis showed 

 these three to be alike, as will be recorded. 



The Merck bicarbonate was thoroughly washed and once recrys- 

 tallized from water. It was then gently ignited, and the normal car- 

 bonate was three times crystallized from water. From this carbonate, 

 by the usual process of precipitation by hydrochloric gas and crystal- 

 lization from water, sample K was prepared. This sample gave 

 essentially the same combining number as the others. 



With such conclusive evidence that no foreign base was present, 

 we turned our attention to the acid. The preceding preparations had 

 all been precipitated with hydrochloric acid gas, obtained simply by 

 warming the highly concentrated purest acid of commerce, because 

 we deemed it more convenient to use this constant material, even if 

 slightly impure, than to prepare so large a quantity of the purest acid. 

 A special set of comparative experiments, made with the purest acid, 

 proved that the other material had, as a matter of fact, been pure 

 enough for the most exacting requirements. 



