Alkali Carbonate Solution. 101 



observed in evaporation residues of intensely alkaline reaction 

 upon litmus paper. This state of things, so completely con- 

 trary to the play of affinities as set forth in our standard books 

 of reference, seemed to call for a special investigation of its 

 cause ; which become the more interesting as the alternative 

 presence of alkaline carbonates, sulphates and chlorids in the 

 alkali soils of the arid region, in spots but a few yards apart, 

 seemed to imply a connection with the above facts. 



It occurred to me that the presence of an excess of carbonic 

 acid, or of "super-carbonates," might be concerned in the 

 apparent anomaly ; since normal alkali carbonates are described 

 as standard precipitants of the earths, even in analytical opera- 

 tions. In looking up the subject in the journals, I found that 

 in 1826 already Brandes (Schweigger's Journal, vol. 43, page 

 156) had called attention to the fact that calcic carbonate is not 

 precipitated from solutions containing only one part in 6,000 

 to 7,000 of water, as observed by him in the investigation of 

 the noted mineral water of Pyrmont. He moreover states 

 directly, that sodium salts dissolved in that amount of water 

 with calcic carbonate form sodic carbonate. It did not occur 

 to him that the free carbonic gas, so abundantly contained in 

 the Pyrmont water, had any part in the reaction. The matter 

 attracted no further attention at the time; later writers 

 attribute the failure of the calcic carbonate to come down 

 under these conditions to " the solvent effect of the alkali salts." 



The next mention of the reaction is made in 1859 by Alex- 

 ander Mueller of Stockholm. He states that carbonic gas 

 passed into a solution of neutral alkali salts, in which calcic 

 carbonate is suspended, forms so large an amount of alkali 

 carbonate as to render the reaction of the solution alkaline. 

 The wide importance of the reaction, however, did not seem 

 to occur to him at the time. 



In investigating the subject I quantitatively followed his pre- 

 cedent; employing solutions of successively greater strength, 

 from one quarter of a gram to a liter up to eight grams, where 

 a critical point seems to have been reached. The compounds 

 used were the sulphates of potassium and sodium ; the calcic 

 carbonate was prepared by cold precipitation with ammonic car- 

 bonate. We thus obtain an exceedingly line precipitate, which 

 readily remains suspended in water, and of which from 5 to 8 

 grams were used in the experiment, so as to insure an excess. 

 With a rapid current of carbonic gas the reaction is usually 

 complete within forty minutes, a longer continuance producing 

 no additional effect. Examination of the sediment then shows 

 an abundance of gypsum, while the solution is intensely alkaline. 



It might be supposed that in this case the difficult solubility 

 of calcic sulphate is a determining factor in the decomposition ; 



