2 GENERAL METHODS 



Measuring cylinders are graduated into cubic centimeters and 

 are used only for rough measurements. 



In order that accurate results may be obtained all instruments 

 used should be correctly calibrated. It should never be taken for 

 granted that a particular instrument is correct, but it should 

 always be subjected to a careful test. Ascertain from the instructor 

 whether the burettes, etc., have been calibrated. For methods of 

 calibration see below. Be certain that you understand how to 

 read burettes and to measure accurately volumes of fluid with 

 pipette, volumetric flask, and measuring cylinder. 



For the gravimetric methods which you are to learn it will be 

 essential that you receive practice in the use of the delicate bal- 

 ances. This instruction may be received at periods to be deter- 

 mined by your instructor. 



CALIBRATION OF VOLUMETRIC APPARATUS * 



All apparatus used for accurate work must be calibrates. 

 Except for that checked by the Bureau of Standards no com- 

 mercial apparatus is entirely reliable, errors exceeding 1 per cent 

 being frequent. 



1 Medical War Manual, No. 6, 1918, p. 71. 



