AQUEOUS SOLUTIONS. MCKAY. 325 



weight of the substance (in this case 58.5), and D for the density 

 of water at 18C, we obtain : 



W+aiv j _ kw w 2 



D v v r 2 ' 



Then differentiating with respect to v, since to is a constant, 



d v .4- 



SW D(l-t% = A1 



v* 



which becomes in the above particular case 



1 



.003m2) ' 



Therefore when m is sufficiently small to make the quantity 

 Zra 2 neligible, the increase of the volume of the solution is equal 

 to the volume of the water added, since in that case 



1 dv _ , 



D dW~ 



Calibration of Flasks, Pipettes and Burettes. 



The flasks were calibrated by weighing them empty and 

 again when filled with distilled water of known temperature up 

 to the mark. The error in calibrating a 250 c.c. flask was deter- 

 mined by a large number of measurements to be possibly .03 

 per cent. No flasks of less volume than 200 c. c. were used in 

 making up solutions. 



With the pipettes, the weight of water of known temperature 

 which they delivered was found. In doing this the point was 

 always held against the receiving vessel, and the liquid which 

 remained in the point after the delivery was removed by blow- 

 ing sharply into it once. The amount of water delivered in 

 this way was determinable to about .005 c. c. 



The burettes used held 50 c. c. and were graduated to tenths 

 of 1 c. c. To calibrate them accurately it was found necessary 

 to determine the volume of the tube for every 2 c. c., and in 

 some cases for smaller lengths. These determinations were 

 checked a large number of times by weighing the volumes of 

 water between very various points on the tube. Readings could 

 be made to .01 c. c., and the calibrations were carried nearly, if 



