Sept. lo, 1917 



Formation of "Black Alkali" 



559 



there was no sodium salt, was subtracted from each of the other read- 

 ings, and the results calculated to sodium bicarbonate. As methyl 

 orange is not sensitive in a concentrated solution of some of the sodium 

 s^lts, the titrations were made by adding an excess of the standard acid, 

 boiling oflf the liberated carbon dioxid, and titrating back the excess with 

 standard sodium hydrate, using phenolphthalein as an indicator. Tables 

 XIX, XX, XXI, and XXII, and figure 11 show the amount of sodium 

 bicarbonate formed in the presence of carbon dioxid. 



After all the determinations had been made and duplicated, an excess 

 of calcium sulphate was added to the solutions and they were again 

 shaken until they had 

 reached equilibrium. 

 This action of the sodium 

 salts upon calcium car- 

 bonate in the presence of 

 gypsum is also shown in 

 the above-mentioned 

 tables and in figure 12. 



In short, a system con- 

 sisting of calcium car- 

 bonate in excess carbon 

 dioxid at atmospheric 

 pressure, and one or more 

 of the three salts sodium 

 chlorid, sodium nitrate, 

 or sodium sulphate, may 

 react toform very appre- 

 ciable quantities of sodi- 

 um bicarbonate. The 

 maximum amount of sodium bicarbonate formed in each system was as fol- 

 lows : With sodium nitrate, i ,386 parts per million ; with sodium chlorid, 1,155 

 parts per million; with sodium sulphate, 5,712 parts per million; with equal 

 parts of sodium chorid and sodium sulphate 2,100 parts per million. 



Table XIX. — Reaction between sodium nitrate and calcium carbonate in the presence of 



carbon dioxid 



^O S5 SO 35 'fO <S SO 55 60 



Fig. 12. Graph showing the same systems as in figure 1:1, with the 

 addition of calcium sulphate in excess. 



