THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 521 



tine needles of a weakly birefracting substance of about 1'525 re- 

 fractive index ; extinction angle large. These needles are evidently 

 selenite (hydrated Calcium sulphate). 



" Preparation II. Precipitate from medium composed of — 



Calcium succinate . . . . 2*0 grammes 

 Magnesium tartrate . . . . 0*2 „ 

 Potassium nitrate . . . . 0*5 ,, 



Sea-water 1000-0 c.c. 



" This preparation consists largely of a cryptocrystalline aggregate of 

 a weakly birefracting substance, whose refractive index is about 1'52 

 to 1*53. This substance proved too fine for further determination. 

 Scattered through this substance are rounded and irregular patches of 

 a second cryptocrystalline substance of strong birefringence, which 

 gives off CO2 when treated with dilute hydrochloric acid, and is prob- 

 ably calcite. 



" Preparation III. Precipitate from a medium composed of — 



Calcium acetate 5-0 grammes 



Sodium phosphate (NaaHPO^, I2H2O) . 0'25 „ 

 Potassium nitrate . . . . 0*5 ,, 



Sea-water lOOO'O c.c. 



" This preparation is again very fine grained, and consists (1) in large 

 measure of minute grains of a substance which agrees with calcite in 

 its optical properties in so far as they could be determined. On im- 

 mersion in dilute HCl a distinct evolution of CO2 gas was observed. 

 (2) Of a substance whose grains are somewhat coarser than the calcite 

 grains, their birefringence being medium to weak ; refractive index 

 about 1'525 ; biaxial and apparently optically positive ; probably 

 selenite, but not crystallized in the usual manner." 



The small quantity of hydrated Calcium sulphate present in these 

 precipitates is imdoubtedly derived from that in solution in the sea- 

 water with which the media were made up, but the reason of its 

 precipitation is difficult to explain since no such precipitation occurred 

 in culture media kept uninoculated under similar conditions as control 

 experiments. It would therefore appear that this deposition of Cal- 

 cium sulphate, along with the Calcium carbonate, must in some in- 

 direct way be the result of bacterial action, and it would seem a 



