Monday, July 18, 2011


        Two test solutions are required A and B. solution A is 62% zinc chloride in water , solution B is I% iodine in a 20% solution of potassium iodide. the test reagent is a mixture of I cc .B and 100 c.c. A it must be freshly prepared .The sample of fibre is wetted out well squeezed and immersed for three minutes in th test solution being then removed and rinsed in water. Swollen cellulose such as cotton is colourless after washing but swollen cellulose such as mercerised cotton or viscose is dark blue being slowly decolonised by washing .The colour is not permanent but if the sample after washing is dropped into a boiling I% solution of Indigo sol Blue O4B the indigo sol is caused to dye the cotton in proportion to the amount of iodine present . Washing in water followed by a short period in boiling soap solution provides a permanent record .Dyed samples may first be stripped without affecting the test.

             This consists in storing wool tops oiled with the oil under test wrapped in paper to keep out dust for periods up t three or four years . samples should be drawn extracted and th extract examined after one two four eight sixteen thirty two and sixty four weeks after the date of oiling . It is always desirable to carry out this test as a final method when examining an entirely new oil .Table LIII shows the figures to be expected from a good quality oil.