CALIBRATION OF VOLUMETRIC APPARATUS 3 



Flasks are calibrated by weighing into them the amount of 

 water necessary to make the desired volume at the temperature of 

 calibration. The following table shows the weights of water over 

 the range of ordinary room temperature which fill a volume of 1 c.c. 

 The figures are corrected for the weights of air displaced by the 

 water and by the brass weights. The water should be weighed 

 to 1 part per 1000, i.e., the water held by a 10 c.c. flask is weighed 

 to 0.010 gm., but a liter flask is sufficiently accurate if within 1 gm. 



Burettes are calibrated by allowing them to deliver distilled 

 water, 2 c.c. at a time, into a bottle and weighing the water. The 

 bottle should contain a layer of paraffin oil a few millimeters thick. 

 This floats on top of the water and prevents loss by evaporation. 

 It is not necessary, therefore, to stopper the bottle. The grams 

 of water noted are multiplied by the volume of 1 gm. at the tem- 

 perature observed. If the results do not agree to within 0.05 

 c.c. (for a 25 to 50 c.c. burette) with the readings the corrections 

 should be plotted on a sheet of coordinate paper, which is hung 

 by the burette for reference. 



The following figures for the first 10 c.c. of a burette serve as an 

 example: 



Pipettes are calibrated by filling to the mark with distilled 

 water and discharging into a weighing bottle. The water delivered 

 should be weighed to within 1 part per 1000. If the mark is not 

 accurate a correct one should be made with a wax pencil, sub- 

 sequently etched in and indicated by an arrow. 



Pipettes may be calibrated for either drainage or blow-out 

 delivery. For drainage the tip of the pipette is allowed to touch 

 the side of the receiving vessel as delivery is finished and a drop of 



