ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
667 
bff a definite quantity of fluid automatically, and of allowing any 
surplus to run back into the flask. 
As will be seen from the illustration (fig. 168) the burette proper 
is quite simple. It is graduated in divisions of cubic centimetres and 
tenths, the zero 0 being at the top. With the main tube two lateral 
tubes are connected, e and a. The latter comes off at an angle of 70°, 
and is provided with a tap. The upper end of e opens into the burette 
just above the zero mark, while the lower end joins the main tube below 
the stop-cock /. Immediately above the zero mark there is a bulbous 
expansion of the burette, and the top is covered with a cap c. 
Fig. 168. 
The fluid to be measured is contained in a Woulf’s bottle with two 
openings. Through one of these passes the lower end of the burette ; 
through the other, a glass tube connected with a rubber tube having a 
ball at the free end. In the ball is a small hole. The fluid is forced 
from the bottle into the burette by squeezing the ball b several times. 
While this is being done, the tap / is open and a finger placed over the 
hole in the ball. When the fluid has risen up above the zero mark 
and perhaps into the bulb, the tap / is closed. The residue above 0 
then runs back into the flask through the side tube e. The desired 
quantities are removed through the side tube a. 
