282 
ELEMENTARY CHEMICAL MICROSCOPY 
however, very small quantities of liquids can be handled, and the 
high speed obtainable will throw out even a precipitate whose 
specific gravity differs but little from the liquid in which it is 
suspended. 
A convenient form of tube for use at high speeds may be made 
as follows: An ordinary glass tube of proper size is drawn out 
to a point in the flame of the blast lamp, and then, by continued 
heating, the glass is allowed to thicken a little at the end; the 
end is pressed, while still soft, against a piece of asbestos board, 
or a piece of charcoal, to flatten it sufficiently to fit well in the 
hematokrit frame. The tube is then cut the proper length, and 
the upper end smoothed with a file or rounded in the lamp flame. 
The turbid liquid to be treated is introduced into the tube by 
means of a pipette with long capillary end, and the tube is then 
placed* in the frame; a similar tube is filled with water to the 
same height, and is placed in the other side as a balance. Thus 
arranged, the machine is turned at such speed and for such a 
time as may be necessary to yield a clear liquid. 
The treatment to which the sedimentation tube is then sub¬ 
jected will depend upon whether the liquid or the sediment (or 
both) is wanted. When the clear supernatant liquid is required, 
it is removed by means of a pipette with long capillary tip. But 
when the precipitate alone is needed the clear liquid is most con¬ 
veniently removed by capillary tubes, made by drawing out odds 
and ends of glass tubing. With such tubes it is only necessary 
to touch the liquid, which will immediately be drawn up by 
capillarity; the tubes filled as far as the force will raise the liquid 
are thrown away. One tube after another is inserted until the 
liquid is lowered to a point just above the sediment. Distilled 
water is introduced, and if the precipitate is to be washed, the 
contents of the tube are mixed well with a platinum wire, and the 
tube is again whirled to effect a separation; for most purposes 
one washing is sufficient. The wash water is removed as before, 
and if the amount of sediment is very small, the tube is cut off 
just above it to enable easy removal of the solid material. The 
upper part of the tube is not wasted, but serves to make capillary 
tubes. These small sedimentation tubes are easily and quickly 
