Viscometry. 



155 



of the cup. Since all but 35 cc. of the oil is run out at each 

 experiment, the rate of flow is constantly changing from 

 the decreasing effect of gravity, and this change is com- 

 plicated by the thickening due to cooling, a varying and a 

 very important function of the rate of flow. Finally, the 

 tubulure being placed at the lowest point of the cup, is 

 sure to be obstructed by any particles of dust present in the 

 oil. Unless the oil in the cup be constantly agitated during 

 the time of the experiment — a condition inconsistent with 

 trustworthy work — it will be found that a sensitive ther- 

 mometer slowly raised and lowered in the oil cup will 

 indicate strata of varying temperatures at the bottom, 

 middle, and top of the cup, and my own observations have 

 assured me that while the main mass of oil in the cup may 

 be at 250° F., that which is passing through the tubulure 

 is, at least, ten degrees lower than this. 





A is a cylindrical vessel of brass, 5 inches in each dimen- 

 sion ; B is a ae-entering cone, 1\ inches high, 1 inch diam. 

 below and J inch at top. Into this are fitted (b}- ground 



