"il 



was closed, while the apparatus was still used like Ostwald's 

 viscosimeter. 



Influence of the quantiti/ of liquid. 



The time of flow depends upon the total amount of liquid in the 

 apparatus. The more liquid there is, the hij^her the surface is in the 

 lower bulb and the smaller is the pressure under which the liquid tlows. 



In Ostwald's viscosimeter the same volume is taken of the various 

 liquids: in this way the influence of the fdling of the viscosimeter 

 is eliminated. When the apparatus is filled with a liquid of high 

 vapour-pressure or liquid gas, it is difficult to fulfil accurately the 

 condition of equal volumes and it becomes necessary to investigate 

 experimentally the influence of the volume of liquid. This can be 

 done by measuring the time of flow of the same liquid, e.g. water, 

 with various fillings. If we then know the weight of another liquid 

 used and its specific gravity, we know the total volume. From the 

 measurements previously made with water we can then find the 

 time of flow for the same amount of water. From the ratio of tiie 

 times of flow (/ and Ar) tlie viscosity {ii) is then calculated by tlie 

 equation 



n : i]ir = dt : c?„, ^H'. 



Influence of capillarit// on the time of floiv. 



In consequence of the capillary action the pressure is not that 

 of the mean difference of height, but is smaller. It is sufficient to 

 make an estimation of this correction. 



The capillary rise in a tube which is placed inside a second 

 tube is given by the formula 



2fj/l 1 



dg\r R — 



in which 6 represents the capillary constant, d the density, r the internal 

 and ?'2 the external radius of the first tube, 7^ the internal radius of the 

 second tube. By this formula the capillary rise was calculated for a series 

 of positions of the liquid surface during the flow; further the volu- 

 mes between the chosen positions were estimated and by means of 

 these the times elapsing between the moments at which the posi- 

 tions were reached. The capillary ascension was then represented 

 graphically as a function of the time and by means of the curve 

 the mean rise was determined. This divided by the mean height 

 of the liquid gives the correction for the capillarity in percentages. 

 For water at 0° with (7=^75.5 we found: mean capillary rise 



