CHAPTER VII.

THE MEANS OF DISTINGUISHING VEGETABLE FIBRES FROM EACH OTHER.

S the fibres when thoroughly bleached are almost pure cellulose, it is

x evident that chemical tests cannot be applied for the purpose of dis-tinguishing one kind from another; but as the incrustating matter can never,on a large scale, be entirely removed, it is possible by chemical tests todistinguish between flax and cotton, the two principal vegetable fibres.

Messrs. Bcettger and Kuhlmann employ for this purpose the yellow-orangecolour caused by the a&ion of caustic alkalies on these fibres. M. Bcettgerimmerses the materials to be tested in a boiling solution of equal parts byweight of water and caustic potassa; they are allowed to remain in thissolution for about a minute, when they are removed and placed between sheetsof blotting or filtering paper, and the excess of liquid expressed. Flax fibreor linen assumes a dark yellow colour, while cotton either remains white orbecomes a very bright yellow. According to M. Kuhlmann, raw cotton, whenplaced in a very concentrated but cold solution of caustic potassa, becomesbright grey, while flax under the same conditions assumes an orange-yellowcolour, which is probably due to^the presence of pe&ic substances, pedtine orpe&ic acid.

M. Kindt states that strong sulphuric acid at the ordinary temperaturedestroys cotton far more rapidly than it does hemp or flax.

When cotton and flax or their tissues are immersed in oil and stronglypressed in order to remove the excess of the liquid, the cotton remains opaque,while the flax becomes transparent.

New Zealand flax may be distinguished from ordinary flax or hemp by thefad that on being immersed in nitric acid of 36° Baume containing nitrousacid in solution, it assumes a red colour, or, if it is first immersed in strongchlorine water and then in ammonia, a reddish tint is imparted, which is notthe case with hemp or flax grown in this country. The best means, however,of distinguishing the different fibres is to examine their minute structure by

the aid of the microscope ; in this way reliable results are obtained.

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