200 Mr. K. Donald. [Nov. 21, 



right-hand end of the tube, or, if the dropping nozzle has great friction, to 

 within 1 or 2 cm. of the end. The vessel of liquid is raised to cover the end 

 of the nozzle. The left-hand end of the mercury tube is then depressed till 

 the pipette is nearly full. Next it is gently raised until the upper meniscus 

 of the liquid rests at the upper calibration mark. Finally the vessel of liquid 

 is lowered. 



Now the end of the mercury tube is raised till the drops fall at the required 

 standard rate, say one per second. The height required for the dropping- 

 point in use is marked by a sliding ring. Then the pipette is refilled, the 

 mercury tube is at once elevated to the required point, and the drop-count at 

 the uniform standard rate is observed. 



If necessary, the mercury tube may be slightly lowered at the last drop to 

 allow estimation of the fraction of a drop. 



The drop-counts for distilled water thus found are given in the following 

 table. The fourth column contains the quotient drop- weight in mgrm./diam. 

 in mm., e.g. for Morse gauge 80, 1000/131/0-340 = 22-45. These quotients 

 are seen to form a fairly uniformly falling curve as the dropping-point 

 increases in size. 



Drop-count. Distilled Water. 



Morse gauge No. 



Diameter. 



Drop-count (20° C.) 

 per 1 c.c. 



Wt. in mgrm. 

 Diam. in mm." 





mm. 







80 



0-340 



131 -0 



22 -45 



79 



0-366 



122 -0 



22 -4 



78 



-406 



112 -9 



21 -9 



77 



0-457 



101 -o 



21 -74 



75 



"533 



87 -0 



21 -6 



72 



633 



73 -5 



21 -4 



68 



0-787 



58-5 



21 -4 



66 



0-838 



56 -5 



21 1 



62 



0-965 



516 



20 -1 



60 



1016 



49 -8 



19 -9 



58 



1-067 



48 -3 



19 -53 



57 



1 -092 



47 -9 



19 1 



54 



1 -397 



38 -9 



18 -4 



52 



1 -612 



34 



18 -25 



43 



2 -261 



25 -5 



17 -4 



33 



2-870 



20-3 



17 -2 



28 



3 569 



16 -7 



16 -8 



At different rates of dropping the drop-count differs as shown by the 

 following observations : — 



