LABORATORY MANUAL 



PART I 

 GENERAL METHODS 



MEASURING INSTRUMENTS 



IN volumetric analysis the instruments most often employed 

 are burettes, pipettes, measuring flasks, and measuring cylinders. 



Burettes are tubes of uniform bore throughout the whole length; 

 they are divided into 'cubic centimeters; they are closed at the 

 bottom by means of a glass stopcock or by a piece of rubber tubing 

 containing a glass bead. The latter form is used as follows: The 

 tubing is seized between the thumb and forefinger at the site of 

 the glass bead ; by means of a gentle pressure a canal is formed at 

 one side of the bead through which the liquid will run out. Instead 

 of the glass bead an ordinary pinchcock is frequently used. 



Pipettes. A distinction must be made between the full pipette 

 and the measuring pipette. The full pipette has only one mark 

 upon it, and serves for measuring off a definite amount of liquid. 

 They are constructed in different forms; usually they consist of 

 a glass tube with a cylindrical widening at the middle; the lower 

 end is drawn out to a fine opening. Measuring pipettes are 

 burette-shaped tubes graduated into cubic centimeters and drawn 

 out at the lower end as with the full pipettes. 



Measuring flasks are flat-bottom flasks with narrow necks 

 provided with a mark, so that when they are filled to this point 

 they will contain a specified volume. They serve for the prepara- 

 tion of standard solutions and for the dilution of liquids to a 

 definite volume. 



