75 



Physics. — "A Viscosunek-i- for volatile liquids \ Hy Prof. J. P. Kuknen 

 and S. W. Visseh. 



In determining the viscosity of a volatile liquid it is necessary to 

 take the measurements in a closed viscosimeter. It is moreover desi- 

 rable that the apparatus should be small, so that it can be easily 

 handled and the temperature can be easily kept constant in all parts 

 and that the liquid does not come in contact with mercury ; the use 

 of mercury at temperatures below its freezing point is in any case 

 excluded. 



In designing an apparatus that should fulfil these requirements, 

 we based ourselves upon Ostwald's viscosimeter ^). His viscosimeter 

 consists of a glass f7-tube with one wide and one capillary arm ; 

 the wide tube has a bulb at the bottom and the capillary tube one 

 at the top. The capillary tube opens at the bottom into a wider 

 tube, which curves into the lower bulb. The time which the liquid takes 

 to pass from the bulb through the capillary tube into the bottom 

 bulb is observed. The experiment begins, when the liquid surface 

 passes a contraction above the bulb, and ends, when it reaches the 

 capillary tube. Before each determination the liquid is drawn up 

 through the capillary or pressed up from the other side. 



The first thing that we tried to do was to make this viscosi- 

 meter into a closed apparatus by joining the two brandies of 

 the f7-tube above into an 0; our intention was to collect the 

 liquid every time in the upper bulb by simply turning the apparatus 

 upside down. 



This was not successful, as the liquid would not join in this posi- 

 tion, some of it remaining in the wide tube above the capillary. 



On this account the bottom reservoir was blown directly on to the 

 capillary tube and the wide tube was then sealed to it in the 

 immediate vicinity of the capillary tube. By this means the ap|)aratus 

 became more compact, as the curved portion of the wide tube 

 disappeared. 



Still liquid remained above the capillary tube, which prevented it 

 readily flowing back. Moreover the time which the liquid took to 

 pass through appeai-ed to depend upon the way in which the liquid 

 flowed out of the capillary tube along the walls of the bulb. 



Finally, the capillary tube was provided with a continuation reach- 

 ing nearly to the bottom of the bulb. When the apparatus is tur- 



^) \V. OsTWALD, Hand- unci Hilfsbucli zur Ausfiihrung physiko-chemischer Mes- 

 sungen, p. 195, 1893. 



