284 
ELEMENTARY CHEMICAL MICROSCOPY 
the type provided in a Spaeth sedimentation glass, as shown in 
Fig. 148. 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 
Fig. 147. Richards Tubes for Centrifugal 
Separations. 
Fig. 148. 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 filtration, 
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 
