244 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



more rapid removal of calcium salts than of magnesium salts 

 by marine organisms in the formation of shells also takes a part. 

 As the result of the operation of these two causes, sea-water, 

 as shown by analysis, contains magnesium-ions in much higher 

 concentration than calcium-ions. 



If a considerable volume of sea-water (one to two litres) 

 be boiled for some hours in a Jena flask, adding from time to 

 time boiled-out distilled water to make up for loss and so 

 drive off excess of carbon-dioxide, a precipitate is obtained, 

 which, on separation, is found to consist essentially of a 

 mixture of oxide and carbonate of magnesium with very little 

 calcium present. 



If the water distilled off be collected, preferably in N/100 

 or N/10 alkali and the amount of dissolved carbonic acid be 

 determined by titration to phenol-phthalem with N/100 acid, 

 the total amount which can be driven off is almost exactly half 

 the figure given in the table for the titration to methyl-orange, 

 while the residue of sea-water left behind in the flask now 

 contains much more " normal " magnesium carbonate, and 

 gives an intense pink with phenol-phthalein. The fact that 

 the carbon-dioxide which can be driven off by boiling the 

 sea- water without addition of acid, or allowing great concentra- 

 tion of salts, is represented by approximately half the titration 

 figure to methyl-orange of the sea- water in its natural condition, 

 demonstrates clearly that the alkalinity is due to a bi-carbonate 

 of an alkaline earth. Analysis of the precipitate formed 

 shows that the alkaline earth chiefly concerned is magnesium. 



This is shown by the two following experiments :— 



Experiment 1. Took 1,000 c.c. of fresh sea- water, and distilled in 

 Jena flask fitted to Liebig condenser, as in sea-water analysis operations 

 for ammonia determinations. Eight successive distillates of 80 c.c. were 

 taken off, the volume being restored in distilling flask at the end of each 

 distillation. In the last distillation the carbon-dioxide coming off was very 

 small. The total titration of the eight distillations was equivalent to 11-47 

 c.c. of N/10 acid; this for 100 c.c. of sea- water would be equivalent to 11-49 



