INFUSORIA AND OTHER ANIMALCULE. 



257 



first ascertained by analysis that this infusorial 

 earth contained 87 per cent, of pure silica. The 

 following method was then adopted to convert it 

 into silicate of soda : 148 Ibs. of calcined carbonate 

 of soda are dissolved in five times their weight of 

 boiling water ; to this is added a milk of lime pre- 





JHI 



Vegetable earth. 

 Infusorial deposit. 



Modern sands. 



I Tertiary formations. 



FIG. 34. Infusorial Deposit, Liinebourg, Germany. 



pared with 84 Ibs. of quicklime. After boiling the 

 mixture for ten minutes or a quarter of an hour, the 

 alkaline liquid, which now contains caustic soda, is 

 decanted off from the insoluble carbonate of lime, 

 and evaporated in an iron vessel, until it has ac- 

 quired a specific gravity of 1*15. At this moment 

 240 Ibs. of the infusorial earth is added. The latter 

 dissolves rapidly in the alkaline solution, and leaves 

 scarcely any residue. If by any accident a smaller 



