VISCOSITY OR FLUIDITY TEST
The test for viscosity, or fluidity, is based on the idea that the greater the tenacity of the glue, the greater will be its cohesiveness, and the less will be its flowing power. In other words, the higher will be its viscosity.
In testing for viscosity, water is used as a standard. A solution is made of the glue, and the rate of flow of the solution at a certain temperature is compared with the rate of flow of water under the same conditions.
Several devices are on the market under the name of “viscosimeter” for measuring the viscosity of glue.
While they vary in detail they are in principle a pipette from which the glue-solution flows at a given temperature. The time required for the glue to run out of the pipette as compared with the time consumed in the same operation by the same quantity of water gives the relative viscosity of the glue.
The viscosity test is not entirely accurate in itself, but taken in connection with the jelly test it forms a very satisfactory basis for grading.