Mention may here be made of Pochin and Wooley's method. Thoroughly dried starch is mixed with 121-25 per cent. of butter-milk or sour milk passed through a sieve of 40 meshes per sq. in., redried, and gently roasted till the colour is yellow to brown.
Experinionts to produce dextrine from cellnloso have been total failures.
Commercial dextrine is never quite pnre, and rarely required to be so, bnt it may be rendered so by first dcoolorizing its aqueons solution by means of bone-black, filtering off, evaporating down, and treating with alcohol to soparate the sugar ; the flocculent precipitate of dextrine is filtered off, dissolved in water, and treated with alcohol, this rotation being repeated 10-12 times. The purifi cation of dextrii le made by diastase is a much more complicated matter.
Commercial dextrine varies widely in quality. It occurs most commonly as a dirty-white or pale-yellow powder, and formerly was made exelusively in this form ; but latterly, it has boen extensively manufactured in lumps bearing a close resemblance to Arabic and Senegal gums. Finally there is dextrine-syrnp, a pale-yellow, transparent, tough, glntinous mass, used by brewers in Franee, but little known elsewhere. An idea of the percentage composition of dextrine intended for industrial application may be gained from the following analyses :— Its composition is so various, and it is so often adulterated, that it should always be bonght on analysis, and carefully tested.
It is very largely used in printing calicoes, glazing paper, gumming envelopes and stamps, making inks and printing-rollers, coating sticking-plaister and bandages, baking bread, and brewing beer. It is said never to be,come mildewed. Its approximate value is 30s. a cwt. in G-cwt. casks..
Dhoura, Thoura, or gum exudes from incisions made in the bark of Anogeissus (Conocarpus] latifolia. The tree inhabits Islamabad, the Kennery jungles, the valleys of Concan rivers, and the inland Dekkan ; it is very plentiful in the Melghat. A good tiptei men of the tree yields about 4 lb. of the gum. It is gathered carelessly, before it is sufficiently d ry to come away by itself, and is much contaminated with bark, leaves, and sand. Picked samples con sist of cylindrical or vermiform tears, i in. (barn., in. long, clear, transparent, almost colour less, forming a clear, colourless mucilage with cold water, but with a small proportion of insoluble bassorine swelling up. When the latter is strained off, the mucilage is quite clear, and as tenacious as arabie. Four reports on an unpicked ordinary sample of the gum placed the probable market value at sums varying from 0 to 25s. a cwt. It was classed as a very low arabic ; but if picked clean, and offered in quantity, it would probably soon command a better price than the maximum estimate.
Dika-mali or Cumbi, and Ouligru5.—Two species of Gardenia, G. lucida and G. gurnmifera [arboreal which are common in many parts of India, yield a resinous exudation ; it occurs in irregular earthy-looking masses of dull olive-green colour, consisting of a mixture of the resin and.
its natural impurities. Its odour is peculiar and very offensive. A spirituous solution is used iu dressing ulcers and to prevent mortification. Both the resin and the twigs coated with it are sold in the Indian bazars.
In New Caledonia, a yellow, aromatic resin, of disagreeable flavour and glossy fracture, is obtained from the buds of G. Ouliepe, G. edulis, and G. sulcata. It occurs as a powder, and in compact lumps. It closely resembles the Indian dika-mali or cumbi, and is ernployed by the natives as a cement and for caulking ships.
Dragon's-blood (FR., Sang dragon ; GER., Drachenblut).—This name is applied to resins obtained from several different species of plants. The most important of the resins, and :the one usually known by the name of dragon's-blood, is afforded by Calamus Draco, of E. Asia. Other kinds of minor significance, which will be described after the chief sort, are (2) Socotran, (3) Canary Islands', (4) W. Indian, and (5) Mexican.
1. E. Asian.—The distribution of Calamus Draco, whose stems constitute the bulk of the rattan canes of commerce, has been recorded under Cane, pp. 595-8. The abundant fruit, on arriving at maturity, is covered with an exudation of red resin, of naturally friable character. This is dislodged by gathering the fruits, and shaking or beating them in a sack or basket, when the freed resin can be sifted clean frorn impurities. Exposed then to the heat of the sun, or of boiling water in a closed vessel, it is softened so that it can be moulded into sticks or balls, which are immediately wrapped in a palm-leaf, generally from Licuala spp. This forms the best kind, or jernang, the " dragon's-blood in reeds " or " sticks," of commerce. The sticks have some times a length of 13-14 in., and a diameter of i-1 in., weighing about 5 oz. ; smaller ones are more comtnon. The surface of the resin appears of an intense blackish-brown ; in thin pieces, it is trans_ parent, and of a pure brilliant crimson. It has a sweetish flavour, and gives a blood-red streak on paper. The sp. gr. is about 1.2, being somewhat higher in the good qualities, and lower in the inferior. These inferior qualities are produced by boiling the pounded fruits in water, and making the resin into a mass, frequently increased by the fraudulent addition of darnmar and other foreign matters. The article is known as " lurnp." It has a slightly acrid flavour, a weaker colour, and a much la] ger percentage (40 or more) of insoluble matters. Dragon's-blood melts at about 120° (248° F.), with evolution of benzoic acid. It is soluble in the alcohols, benzol, chloro form, carbon bisulphide, the oxygenated essential oils, petiolenni-ether, glacial acetic acid, and caustic soda ; sparingly so in ether. and still less in turpentine-oil. It is largely sent into Chinese, Indian, and European commerce from Singapore, Batavia, and Banjarmassing. It is used as a colouring agent in pharmacy, but much more extensively for making varnishes, particularly those ernployed by furniture-polishers.