1912.] An Apparatus for Liquid Measurement by Drops. 201 



Diameter. 



Sec. 

 per drop. 



No. of drops obtained. 



Dropping-tube (throttled on separator 

 cylinder with Mariotte's tube) 



Dropping-tube similarly fitted 



Mercury tube pressure, Morse 33.. 



„ „ Morse 56.. 



„ „ Morse 80.. 



D.P. VIII 



Hand-teat pressure, D.P. X 



mm. 

 1-4 -4 



2 -87 



1 -181 



-34 



0-29 



25 





 

 1 



2 





 2 





 1 

 2 

 3 

 4 

 12 





 

 1 

 1 



3 





 

 1 

 2 





 

 1 

 1 

 1 

 3 





 

 1 



41 

 41 

 42 

 46 



84 



22 

 23 

 23 

 23 

 24 

 24 



45 

 46 

 50 

 51 

 51 



68 

 67 

 66 

 67 



95 

 90 

 86 

 86 

 86 

 86 



116 

 106 

 99 



from 10 c.c. 



5 









 



2 from 1 "125 c.c. 







2 



9 



3 



6 





 

 

 3 



from - 5 c.c. 

















 

 4 

 1 

 2 

 4 





 



From the above observations it may be seen tbat just in the cases where 

 fine accuracy is most desirable — namely, in measuring by hand one or two 

 drops — these small drops have in their favour the peculiarity (pointed out 

 by Ollivier) of being practically constant in weight at all expulsion-rates 

 slower than one drop per second. Such rates can be easily and reliably 

 secured by the use of a hand mercury-plunger tube — a miniature form of 

 the mercury tube described above. 



The narrow limits of drop-rate required for large drops, e.g. of 1/5 to 

 1/4 c.c. in the Wassermann test, may be secured by the use of the arrange- 

 ment shown in fig. 2. 



A separate cylinder of convenient size has a small Mariotte's tube fitted 

 by a rubber cork through the upper aperture. Various dropping-tubes, 

 smaller to telescope inside, or larger to telescope outside the stopcocked 



