THE CHEMICAL EXA^HNATION OF THE MATERIALS FROM FUNAFUTL 87i» 



pointed out by the late Mr. E. T. Hardman, this seems only to be true when 

 ammonium salts are present ; while direct experiments, with solutions not containing 

 the ammonium salts, give very difierent results. 



In 1848 Professors W. B. and R. E. Rogers described a series of experiments 

 which they had made upon the solvent action of pure water, and of water containing 

 carbon dioxide, on various minerals and rocks. By agitating powdered mixtures of 

 the calcium and magnesium carbonates in flasks containing water with carbon 

 dioxide, they found that the magnesium salt was dissolved faster than the calcium 

 salt.* 



A directly opposite result to this was, however, obtained by Gustav Bischof, 

 from experiments described by him in his well-known ' Lehrbuch der Chemischen 

 und Physikalischen Geologie.' In these experiments, magnesium limestones of known 

 composition were finely powdered and mixed with water, through which carbon 

 dioxide was passed for twenty-four hours. The liquids, when filtered ofi" and 

 analysed, yielded a considerable amount of calcium carbonate, but only traces of the 

 magnesium carbonate. Bischof also suggests that dilute acetic acid behaves in the 

 same way as carbonic acid, dissolving out calcium carbonate more rapidly than 

 magnesium carbonate from a mixture of the two salts, f 



The effect of even moderate pressure in modifying the solvent action of carbon 

 dioxide on the magnesium and calcium carbonates is a fact well known to chemists. 

 Based upon this principle, a process was for some time employed for the commercial 

 extraction of nearly pure magnesium salts from dolomite, which consisted in subjecting 

 the rock, when finely ground and mixed with water, to the action of carbon dioxide, 

 under a pressure of ahout four atmospheres. Under these conditions the magnesium 

 carbonate passed readily into solution while very little calcium carbonate was taken up.;]: 



Hardman, in 1876, repeated on a much more extended scale the experiments of 

 Bischof, and proved conclusively that when magnesium limestones broken into small 

 fragments are submitted to the slow action of water containing small quantities of 

 carbon dioxide, the calcium carbonate is dissolved at a much more rapid rate than 

 the magnesium carbonate. § 



In 1894 it was shown by Hogbom,|| that when calcareous organisms are treated 

 with dilute acetic acid, the quantity of magnesium which passes into solution is 

 very insignificant, as compared with the quantity of the calcium salt dissolved. He 



* ' Amer. Journ. Sci.,' 1st series, vol. 5 (1848), pp. 401-405 ; also in ' Edinb. New. Phil Journ.,' 

 vol. 45 (1848), pp. 163-168; and ' Brib. Assoc. Rep.,' 1849, PI. 2, pp. 40-42. 



t ' Chemical and Physical Geology ' (Cavendish Society), 1858, pp. 194-196. 



X 'Dingl. Polyt. Journ.,' vol 209, p. 467; abs., ' Chem. Soc. Journ.,' vol. 12, p. 96. 



§ 'Roy. Irish Acad. Soc. Proc.,' 2nd series, vol. 2 (Science), pp. 705-730. 



II ' Neues Jahrb. fiir Min.,' &c. (1894), vol. 1, p. 271. The first author who suggested this enrichment 

 of a rock with magnesium salts by the gradual leaching out of calcium salts appears to have been 

 Grandjean, in his Memoir on " Die Dolomite und Braunstein-Lagerstatten im untern Lahnthal," ' Neues 

 Jahrb. fiir Min.,' &c. (1844), pp. 543-553. 



3 C 2 - 



