367 



If direct determinations of the carbonic acid, or otiier 

 gases, in seawater are to be made in the future I must recom- 

 mend the use of the mercury-pump as the only really accurate 

 and convenient apparatus for the extraction of gas. There 

 can be no serious difficulty in its adaptation for use on 

 board ships. 



If my experiments are repeated with really «normal» sea- 

 water and a final value obtained for the constant of dissociation 

 the easiest, and for all practical purposes a sufficiently accurate, 

 method of quantity-determination will be to determine the tension 

 and alkalinity of the water and to compute the quantity by 

 means of the formulas given above. 



Tlie carbonic acid of freshivater. With regard to fresh- 

 waters very httle theoretical work has been done. The chief 

 alkaline, and in most cases the chief saline component also, is 

 carbonate of lime. Schloksing {Compt. rend. T. 74 p. 1552, 

 T. 75 p. 70) has studied the solubility of this salt in pure 

 water and in water, saturated at varying tensions with carbonic 

 acid, and has arrived at the following results. 



Carbonate of lime is soluble in water to a certain extent 

 irrespective of the carbonic acid present — 1 1. of water at 16"^ 

 is, according to Schloesing, capable of dissolving 13.1 mgrs. of 

 Ca CO.^ \) — but beyond this the salt is dissolved as bicarbonate 



') Anderson (Froc. Roy. Soc. Edinbim/h, vol. 1(J, 1889, p. 324) has 

 determined the solubility of calcspar, coiai powder and amorphous cal- 

 cium carbonate in distilled water and found that 1 liter dissolves 25.1, 28.5 

 and 248 mgrs., respectively. Though his results are perliaps vitiated 

 by atmospheric carbonic acid and therefore too high, I have no doubt 

 that ScHLOESiNGS figure is too low. CaCO^ is certainly not less 

 soluble than BaSO^. It is probable that Schloestnc; has experimented 

 upon crystalline carbonates and that, on this account, his results are 

 not directly applicable to solutions of the amorphus lime. 



