finally retains. A defect possessed by both forms is the retention of a
drop of varying size in the nozzle. Whatever method is adopted for
removing this drop must be always adhered to. The most convenient form
is the one last described, and the most useful sizes are 100 c.c., 50
c.c., 20 c.c., 10 c.c., and 5 c.c. Ten c.c. pipettes graduated into
tenths of a cubic centimetre are very useful: those are best in which
the graduation stops short of the bottom.

All measurements should be made at the ordinary temperature; and, before
being used, the pipette should be rinsed out with a cubic centimetre or
so of the solution to be measured. After using, it should be washed out
with water.

~Burettes~ differ mainly from pipettes in having the flow of liquid
controlled from below instead of from above. The best form is that known
as Mohr's, one kind of which is provided with a glass stopcock, while
the other has a piece of india-rubber tube compressed by a clip. The
latter cannot be used for solutions of permanganate of potash or of
iodine, or of any substance which acts on india-rubber; but in other
respects there is little to choose between the two kinds. A burette
delivering 100 c.c., and graduated into fifths (_i.e._, each division =
0.2 c.c.), is a very convenient size. For some kinds of work, 50 c.c.
divided into tenths (_i.e._, each division = 0.1 c.c.) may be selected.

Burettes may be fixed in any convenient stand; they must be vertical and
should be so placed that the assayer can read any part of the graduated
scale without straining. When not in use, they should be kept full of
water. When using a burette, the water must be run out; the burette is
next rinsed with some of the solution to be used, and drained; and then
it is filled with the solution. Next squeeze the india-rubber tube so as