6.1 Apparatus

The details of the viscometer have been given in IS: 1091-1976, 'Specification for Nitrocellulose'.

6.2 Procedure

The viscosity of Nitrocellulose solution is determined by the failing - sphere method using a steel ball of 1.58±0.01 mm diameter. A solution of the requisite concentration is prepared by adding a fixed weight of dried Nirtrocellulose (see table below) in 100 ml of 95% v/v aqueous acetone (relative density 0.8097 at 20°C) taken in a glass tube 45 cm long & 2.5cm internal diameter. The tube is securely stoppered, shaken by hand to prevent the caking of the Nitrocellulose into a hard mass than rotated on a wheel untill the number is homogenous and free from any lumps. The solution is transferred to the viscometer, which is stoppered and in a vertical position in a thermostat maintained at 20±0.1°C. The solution is allowed to stand until quite free from air bubbles and it has attained the temperature of 20±.1°C. The stopper of the viscometer is then replaced by the one carrying the release tube and the steel ball introduced into the solution through this device. (The time of fall of the through 15 cm is noted).

Similar determination is made using castor oil of known viscosity in place of nitrocellulose solution.

6.3 Calculation

Viscosity, in poises = T (S-S1) T1(S-S2) x viscosity of castor oil in poises

where
T = Time of fall (in seconds) in the nitrocellulose solution
T1 = Time of fall in the castor oil
S = Density of steel ball
S1 = Density of Nitrocellulose Solution at 20°C
S2 = Density Of Castor Oil (Viscosity of Castor Oil at 20°C = 9.65 Poise)

Sample size for Falling Sphere Method of Viscosity Determination