Graduation and Calibration of Apparatus 149 



given below. A burette is graduated first, and calibrated after- 

 wards. The graduating is a very awkward performance, as it 

 involves the dividing of a line into a large number of equal 

 parts, and the accurate transfer of these small 

 divisions. 



The burette is an instrument used to deliver 

 large amounts of liquid in small quantities at a 

 time, hence it must be graduated by a method 

 which gives accuracy under such conditions. 



The stem is waxed as before, and a mark 

 made high up, for the zero point. A dry 

 weighed beaker or weighing bottle is next taken, 

 the temperature of the water to be used deter- 

 mined, and the mass of 50 c.c. of water calcu- 

 lated. This weight is then recorded, being 

 added to those already in the balance pan, and 

 the water is filled into the burette, up to the 

 zero mark already fixed, the bottom of the 

 meniscus being coincident with the mark. If 

 preferred, a burette float may be used The 

 water is now allowed to drop from the burette 

 into the weighing bottle a drop at a time, 

 until roughly the 50 c.c. have escaped, when 

 the bottle and contents are weighed. A few 

 drops (say 20) are again allowed to fall, and 

 the bottle again weighed. A simple calculation 

 will now give the number of drops still required 

 to complete the 50 c.c., and these are allowed 

 to fall, tested by weighing, and corrected if 

 necessary. The burette is now marked through 

 the wax, and the 50 c.c. volume recorded. 

 This has now to be divided into ten equal fives. 



With a fine pen and in good black ink draw 

 a long line upon a piece of drawing paper well 

 stretched out upon the bench, and transfer to 

 this line the distance between the two marks, by placing the 

 marked burette upon the paper along the line, and pricking 

 down with a sharp needle at each mark, dividing the line so 



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