A Modified Ostwald Viscometer The principle of an Ostwald viscometer is based on the time of flow for a given volume of liquid through a precision capillary. This type of viscometer is very convenient for measuring viscosity of liquids a t a fixed temperature. But i t has same disadvantages when one intends to measure viscosity as a function of temperature. With increase of temperature, the opposing hydrostatic head does not remain constant, While this does not affect time of flow very appreciably over a small temperature interval, the effect is pretty serious when one has to work over a wider temperature range. We describe herein a design of Ostwald viscometer in which the opposing hydrostatic head is maintained constant. In this design as sketched in the figure, the excess overflowing liquid will flow into the cup D and the opposing hydrostatic head is thus maintained a t a constant value till the level of the liquid in the cup D exceeds the top of the reservoir E. In this way the level is maintained a t a constant height. We have successfully employed this type of viscometer for measuring viscosity of melts of organic compounds over a temperature range of about 100°C. By way of illustration we have recorded in the table the viscosity ofp-diehlorohenzene melt from its melting point to ISO'C, the corresponding densities being determined by employing a dilatometric technique described by AlMahdi and Vhhelohde.' 01 Al-Mahdi,
E-
A. A. K., and Uhhelohde, A. R., Proc. Roy. Soc (London) A, 220, 143(1953). Viscosity and Density of p-Dichlorobenzene Melt
Modified viscome'er's'c'Fiducia1 marks: D. cup: E, reservoir. ~~
f"C
58.5
70.0
77.0
89.5
99.0
112.0
119.0
140.0
(millipaise)
0.622 1.216
5.772 1.201
5.210 1.194
4.536 1.180
4.202 1.169
3.753 1153
3.538 1.147
2.828 1124
~
(g/cc,
Biswanath Bhattacharyya Dilip K. Majumdar University of Kalyani Kalyani, West Bengal, India
194
/
Joornai of Chemical Education
