ALKALIMETRY. 



243 



The dropping-tubes or burettes employed for these 

 analyses with standard solutions, are made of different 

 forms. The commonest is that represented in Fig. 30 , 



Fig. 30. 



and consists of a glass tube, closed at one end, about 

 0.25 metre (or 12 inches) long, and 0.01 metre (or f 

 inch) in diameter ; into the lower part of this tube is 

 cemented another, very much narrower, which is fixed 

 parallel with the larger tube ; the extremity of the 

 small tube is bent outwards and sharply cut off, so 

 that the liquid may be conveniently poured from it. 

 The whole of the vessel is divided into known volumes, 

 and it is preferable to take from 25 to 50 cub. cents., 

 and to divide these into fractional parts. The zero 

 should be placed at the top of the scale, below the 

 level of the orifice of the spout. 



Another form is that shown in Fig. 30 b, which 

 consists of a single divided tube furnished at the top 

 with a spout, and with an orifice for pouring in the 

 liquid. 



A third form of burette, which is the most suitable 



