236 



ELEMENTARY CHEMICAL MICROSCOPY 



the type provided in a Spaeth sedimentation glass, as shown in 

 Fig. 125. Upon being whirled in the machine the suspended 

 matter is forced into the conical cavity in the stopcock; a quarter 

 turn of the stopcock completely cuts off the sediment from the 



Cork 



FIG. 124. Richards Tubes for Centrifugal 

 Separations. 



FIG. 125. Sedimentation Fun- 

 nel for Large Centrifugal 

 Machines. 



liquid and the latter can be poured off without danger of disturb- 

 ing the sediment; the stopcock can then be removed, and the 

 contents of the cavity, containing only a very small volume of 

 the solution and all the suspended matter originally present, 

 subjected to examination and analysis. 



Filtration. In spite of every precaution it frequently happens 

 that decantation will not yield a sufficiently clear liquid for sub- 

 sequent reactions, or that the precipitate cannot be freed of the 

 mother liquor, and that centrifugal separation cannot be used. 

 Under such circumstances recourse must be had to nitration, 

 which is doubtless one of the most troublesome processes of 

 microchemical work. Since, in the majority of cases, the amount 

 of liquid to be filtered consists of two or three small drops, often 

 less, methods involving the use of a funnel, be it ever so small, 



