Cuprammonium fluidity test:

This is a senstive index for the determination of chemical degradation of cotton cellulose during scouring, bleaching, souring, etc. In this test, the condtional cotton sample required to make 0.5% solution is exactely weighed and dissolve in cuprammonium hydroxide solution. The flow time of this solution between two fixed marks on a calibrated viscometer (fluidity tube) is measured at specific temperature. The fluidity value "F" is then calculated from the flow time "t" and the viscometer constant "C" by using the fomula F=C/t. For flow time of 200 seconds or less, a kinetic energy correction k has to be applied which is given in the calibrated certificate. The results are expressed as rhes (poise^-1) , which is the reciprocal of the unit of viscisity. Fluidity values between 5-8 are considered to be satisfactory for normal bleached fabric. Determination of cuprammonium fluidity (which in turn indicates the degree of polymerisation, DP) is a senstive test for fabrics of 100% cotton.

In the case of 100% viscose fabric, a 2% solution in cuprammonium hydroxide (instead of 0.5% for cotton) may be used which is likely to show a fluidity value of about 8.  

Preparation of Cuprammonium Solution: A solution containing 240±5 g of ammonia (NH3) and 15±0.1 g of copper per 1,000 ml is satisfactory for the dispersion of cellulose of different forms, including cotton fibers which have not been subjected to any drastic chemical processing.