At the bottom, a row of wooden slats, about 2 1/2 in. broad, 1/2 in. thick and 13 in. long, are placed edgeways, and upon these the weed is laid carefully piece by piece in the frame, the sides of which are kept in position by a rope stretching across the top; a movable plank at the back, which is raised as the workman proceeds, keeps the weed thoroughly even. When the frame is full - about 2 tons going into one press - a similar lot of slats to those at the bottom are placed on the top of the seaweed, and the whole is pressed as tightly as possible by means of a rough capstan, to get rid of all unnecessary moisture, and to render the mass firm enough for cutting. The frame is then laid down flat; and one of the side planks being removed, the compressed weed is planed with an ordinary carpenter's plane, so as to cut it to the required thickness - about 1/20 in. - along the edges and with the grain. The object of the slats is to enable the workman to plane to the edges, and they are removed one by one as he progresses with his work. Each man can plane on an average 170 lb. of seaweed per day.
After planing, the cut seaweed is taken out of doors and shaken out to dry on mat?; under favourable circumstances, one day is sufficient for this operation, but it frequently happens that as many as 3 days are required before it is dry enough to pack away. After the final drying, the weed is ready for the market, and is packed away in boxes containing about 66 lb. each. The rejected ends of the first-class seaweed are used up together with ordinary long seaweed of an inferior quality, to make cut seaweed of a lower class. While undergoing the various processes, the material loses 20 per cent, in weight, and that fact, joined to the price of the labour expended in its manufacture, brings the cost to more than double the average of long seaweed. (Soc. Arts Jl.)
Tkao is a very interesting substance, and one which is likely to come into considerable demand in the future. It is a gelatinous preparation made in Cochin China, as well as in other eastern countries, from seaweed. In the English market, it has frequently appeared, under the name of Chinese or Japanese isinglass, in three different forms. That which is prepared in Cochin China is in bundles of threadlike pieces a foot or more long, about the thickness of whipcord. The specimens prepared in Japan occur in two forms, one in square sticks about 11 in. long and 1 to 1 1/2 in. in diameter, and full of cavities, each weighing only about 3 dr.; and the other in bundles of long shrivelled pipe-like pieces about 1/8 to 1/4 in. in diameter and about 14 in. long. The bundles are fastened at the ends with the stems of some grass. When immersed in water, these pieces are seen to have the same square shape as the other varieties. One side of the pieces is always more full of diatoms and other foreign bodies, as if the pieces had been formed in a mould in which the sediments of the jelly had gone to the bottom. The cord-like variety made in Cochin China is in long loose bundles.
It has much the polished appearance of the Chinese vermicelli made from rice, but that substance will not bend and is much more slender. Various trials have been made with it in France since 1874, especially by D. Gantillon and Co. at Lyons, and the Industrial Society at Rouen. The thao is prepared for use in the following way: - After having been soaked in cold water for about 12 hours, it is boiled for J hour, during which it absorbs about 100 times its weight of water. If allowed to cool, it becomes a jelly; but if passed through a sieve and stirred until cold, it remains fluid, and in this state is more easily employed than when hot. The yellowish matter which some specimens contain can be removed by boiling for some time, when it forms an insoluble scum which appears to consist of very thin fibres, and which remain attached to the sides of the vessel. A singular property, and one which perhaps might be turned to valuable account, is, that thao jelly does not decompose solution of permanganate of potash, even when left in contact with it for 24 hours.
According to Heilmann, of Rouen, thao produces, in the proportion of 1 part to 100 of water, a dress ing which is supple and strong, and which gives substance rather than stiffness to calico; while dextrine, like starch, make the tissue drier and harder, and gives less facing to the thread. The addition of glycerine gives a dressing still more flexible and soft, and while rendering the tissues less stiff it communicates more body to them. The addition of talc gives still greater smoothness. Once dissolved, according to Gantillon, thao will mix while hot with any gum, starch, dextrine, or gelatine. The principal advantages of thao in dressing silk fabrics is, that while preserving their suppleness it gives them greater glossiness and makes them soft to the touch. The mixture of thao with gum tragacanth is said to be the best method of using it. Thao should, however, be used alone for materials which it is not necessary should be stiffened. As thao is only soluble at a high temperature, a moist atmosphere, fog, or even rain does not affect the material dressed with it. It combines well with sulphate of copper and the chlorides of aniline and potassium, and can be used in double dyeing. It also answers well for sizing paper, etc. The only obstacle to its extensive use is its high price.
There is, however, no reason why a similar substance should not be made from our common native seaweeds, of which Gelideum corneum and Qracilaria confercoides approach most nearly in character the algae from which thao is made. Gelose, of which thao consists, differs from the carra-geenin obtained from Chondrus (rispus in its power of combining with a very large quantity of water to form a jelly; it yields 10 times as much jelly as an equal weight of isinglass. For purposes of food, thao jelly is not quite so pleasant as animal jelly, as it does not melt in the mouth; it also contains no nitrogen. A great advantage which it possesses is, that it is but little prone to undergo change - so much so that the jelly is sometimes imported from Singapore, sweetened, flavoured, and ready for use, and may in this state be kept for years without deterioration. The west coast of Australia also yields a seaweed possessing similar properties. Porphyra vulgaris (the " laver " of English coasts) is given as the source of the seaweed isinglass in square sticks. In Cochin China, this variety appears to be known under the name of mat.
A number of other seaweeds are, however, collected, and are known to the Annamites under the general name of rau-cau, while in Chinese medicine they are called hai-thao. These algae are gathered in considerable quantities in the islands of Cu-lao-Khaoi and Cu-lao-re*, those collected in the latter being considered of the best quality. (Pharm. JL)