A new Finishing Material for Cotton.

Practical Magazine 19, 1876

(Chemistry applied to the Arts, Manufactures, &c.
Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

According to an article in the "Bulletin de Rouen" by M. J. J. HEILMANN, a new finishing material for cotton has been discovered in "haï-thao," or gelose, which is obtained from a species of alga or sea weed, occurring frequently in Cochin China and Mauritius. It appears in the form of coarse flat threads, which are hard and tough, and 30 centimetres (about a foot) long. It is without taste or smell, consists of a transparent colourless mass, and is covered with a net-work of opaque veins, in reality nothing but folds, which appear on drying the substance. It is not soluble in cold water, but only swells up. It does not dissolve below 167°Fahr., and then only partially. For complete solution it must be in boiling water at least ten minutes. Then all the flock disappears in the fluid, and a transparent, thin, dirty-white solution is obtained, which does not stick to the fingers. On cooling the haj-thao separates, like gelatine, as a yellow-greyish jelly, which is again dissolved by boiling. The jelly has neither an acid nor an alkaline reaction, and even after having been long kept, e.g., for eight days, shows no tendency to fermentation or putridity.

Thao can be dissolved in cold concentrated sulphuric acid, hydrochloric acid, or nitric acid, and will again separate from these solutions on the addition of water. Towards alkaline solutions it behaves in the same way as towards water. In alcohol, whether cold or boiling, it is perfectly insoluble. It is not softened but hardened by it, and after the evaporation of the alcohol is no longer transparent.

It appears from M. Heilmann's experiments, that it can be used as a finishing material for cotton only when boiling hot. If the watery solution gets cold, it must be boiled up again to be of any use. With a dilution of one part of thao in 300 of water, the solution begins to make itself perceptible on a textile fabric as a light finishing. If one part of thao to 100 of water be taken, the fabric acquires a rather strong but soft touch; it gains in body but not in stiffness. If this finishing material is compared with potato starch and dextrine, it is found that a dextrine finishing of 50 grammes (about 1¾ oz.) per litre (1¾ pint) gives goods less firmness than the one per cent. thao finishing, but one of 100 grammes (3½ oz.) per litre gives them more, while on the contrary 50 grammes of potato starch boiled in water produce greater stiffness.

Both the dextrine and the potato starch fill the threads less than the thao, and make the texture much drier and rougher. An addition of glycerine to the thao solution, even when some potato starch is mixed with it, produces a still softer and at the same time stronger finishing. The addition of a mineral finishing material, such as talc, pipe-clay, &c., gives the goods a greasy touch, and they feel much more tender and delicate than if treated with a decoction of dextrine or potato starch. Moreover, thao finishing continues on the texture in cold water, while dextrine and potato starch soften and dissolve in it. Thao should never be used without ultramarine, because it gives the cotton a yellow tinge. Even with ultramarine a greenish tinge is observable. Lastly, on checked goods it has the property of contracting them.

Heilmann comes to the conclusion that thao should be used only for fine fabrics, to which it is desired to give a soft and at the same time solid touch, but it is not suitable for taking the place of dextrine or potato starch where it is desired to give a heavy stiff finishing. The price also of this product must be considerably reduced before it can compete successfully with the other two substances.