Title: Determination of Jelly Strength
- Objective: To determine the Jelly Strength of Gelatin to provide information on the purity of the substance.
- Principle: Determination of the force (in grams) which has to be applied by means of a cylindrical piston, 12.7 mm in diameter to the free surface of 6.67 % w/w matured at 10° gelatin gel in order to produce a depression of 4 mm.
3. Procedure:
- Apparatus:
A gelometer consisting of a cylindrical piston 12.6 to 12.8 mm in diameter with a plane pressure surface with a rounded edge 0.5 mm in radius attached to a device whereby the load exerted by the piston can be increased at a constant rate of 40 g per second and the vertical movement of the piston can be stopped within 0.025 seconds when it has descended 3.9 to 4.1 mm.
- Method:
Place 7.5 g of the substance being examined in a bottle, 58 to 60 mm in internal diameter and 85 mm high, add 105 ml of water, cover the bottle with a watch glass and allow to stand for 3 hours. Heat in a water-bath at 65°C for 15 minutes, stirring gently with a glass rod ensuring that the solution is uniform and that any condensed water on the inner walls of the bottle is incorporated. Allow to cool at room temperature for 15 minutes, transfer to a water-bath maintained at 9.9°C to 10.1°C and ensure that the base of the bottle is horizontal. Close the bottle with a rubber stopper and allow to stand for 16 to 18 hours. Immediately transfer the bottle to the gelometer and adjust the height of the bottle so that the piston just comes into contact with the surface of the gel without exerting any pressure. Increase the load on the piston at a rate of 40 g per second until it has descended 3.9 to 4.1 mm. The load, measured within a precision of ± 0.5 g, exerted by the piston at that moment represents the jelly strength. Carry out five determinations and use the mean value.