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kinds of shellac varnish, where colour is not so much an object; for the best qualities of spirit varnishes only orange shellac is used.
Of late years some improvements have been adopted in one or two large lac factories in India. The lac is better washed, whereby more colouring matter is extracted from the crude lac; then, the appliances for melting and straining and converting the lac into its shell form are considerable improvements on the primitive methods described above.
Lac comes into commerce in three forms—shellac, in thin flakes of an orange colour, varying a little in shade and transparency; button lac, in large round flat masses of a dark colour; and as garnet lac, in irregularly shaped flat pieces of a dark ruby colour. It is rather brittle and easily broken up into small pieces. Occasionally it is artificially coloured with orpiment or mixed with rosin, but such adulterations are rare.
Lac is incompletely or only partially soluble in alcohol or nethylated spirit, forming a turbid brownish-orange solution, which is largely sold as French polish and varnish for cabinet and other work; it is soluble in amyl alcohol.
Lac is only partially soluble in ether, chloroform, and turpentine, while it is insoluble in petroleum spirit. It is soluble in solutions of caustic potash, and of caustic soda to dark red solutions. In borax solution and in weak ammonia it is also soluble, and such solutions are sometimes used as water varnishes. One point of interest in the solubility of shellac in such alkaline liquors is that the colouring matter is first dissolved away from the resin proper, leaving the latter of a pale colour; this property is taken advantage of in preparing white shellac. Chlorine passed through alkaline solutions of lac throws down the resin free from colour. Lac has a specific gravity of 1:113 to 1.214, the darker varieties being the heavier.
Crude stick lac freed from woody matter contains 66.67 per cent. of resin, 6 per cent. of wax, 6 per cent. of gluten, and 10-8 per cent. of colouring matter. In shellac five distinct resins have been separated—(1) resin soluble in alcohol and ether; (2) resin soluble in alcohol, but insoluble in ether; (3) resin slightly soluble in alcohol; (4) a crystallisable resin; and (5) an uncrystallisable resin. These constitute about 90 per cent. of the shellac. There are in addition (6) fatty matter; (7) wax; (8) gum; and (9) colouring matter.
Bleached or White Shellac.—Shellac may be bleached in two or three ways. One method is to boil ordinary shellac in a weak solution of carbonate of potash, and when dissolved passing a current of chlorine through it; the lac precipitated is collected, melted under water, and then, while soft, pulled so as to give it
a fibrous satiny appearance.
Another method is to boil the shellac in a weak solution of potash, and, while melted, pulling and working together until the desired whiteness has been attained. Then the shellac is remelted and repulled in clean warm water. White shellac is sold in the form of long cylindrical pieces having a fibrous satiny appearance. It is used for making white varnishes and for other purposes where a white shellac is required; as it is sold in rather a wet condition it is necessary to dry it before using it. White shellac deteriorates on keeping, becoming insoluble in alcohol and borax.
Elemi.- Under this name several varieties of a resinous matter come into commerce which are used as a softener or toughener for varnishes.
1. Manila Elemi.—This comes from the Philipine Islands and is the product of a tree known as Canarium commune to botanists, which principally grows in the island of Luzon; the supply is sent through Manila. This variety of elemi is white when quite pure and of good quality, although some samples have a grey appearance and others appear to be composed of two or three sorts of resins. The resin is soft and has a granular appearance ; when exposed to the air for some time it becomes hard, owing to the evaporation of the volatile oil present in freshly-gathered elemi. The odour is slightly turpentiney.
When distilled this eleri yields about 10 per cent. of an oil resembling turpentine in its composition. Elemi begins to soften at about 750 to 80° C., and is quite liquid at 120° C. It is soluble in alcohol and in most other solvents. It is used in varnishes to give elasticity or toughness.
2. Mexican Elemi.—This variety is obtained from a tree known as Amyris elemifera. In its essential properties it resembles Manila elemi, but is rather darker coloured and harder in appearance and consistency. It is not very common.
3. Brazilian elemi is supposed to come from trees belonging to. the genus Icica, but is not an article of regular importation into this country:
4. Mauritius elemi is supposed to come from the tree Colophonia Mauritiana, and is stated to resemble Manila elemi in appearance and properties.
Benzoin.-Gum benzoin or gum benjamin is a balsamic resin which exudes from Styrax benzoin, a native of Sumatra, Java, Borneo, Siam, Laos, and other places in the same region. The commercial product comes principally from Siam and Sumatra. The Malays know it by the name “kaminian.” In the coast regions of North and East Sumatra it is cultivated from seed. In about seven years it obtains a diameter of 6 to 8 inches and is
then ready to be cut. The natives make incisions in the tree and the resin exudes from them very freely, each tree yielding about 3 lbs. annually; for the first three years the product is of firstclass quality, of a yellowish-white colour and soft with a fragrant odour; after the third year the product is darker in colour, harder and not so fragrant; after about nine years it is not worth collecting. In the interior regions the resin is collected from wild trees.
The benzoin imported into England mainly comes from Siam and Sumatra. The two varieties differ slightly in appearance and properties.
Siam benzoin occurs either in agglutinated, flattened, somewhat opaque, milk white tears or in large agglomerations of white masses distributed through an amber-coloured, rather translucent matrix. It is brittle, and has a strong characteristic vanilla-like odour. It is readily softened by heat; it is quite soft at 75o C. and fluid at 100° C.
Sumatra benzoin is rather greyer, and is in the form of an agglomerate mass with white tears distributed through a darker translucent matrix. Its odour is not so strong as that of Siam benzoin and it does not melt so easily.
Ludz states that it contains about 12 to 15 per cent. of ligneous matter. The resin contains cinnamate of benzoresinol, 5 per cent. ; cinnamate of resinotannol, 64 per cent. ; cinnamic acid, 30 per cent.; with small quantities of vanillin and benzoic acid; it is therefore a source for the preparation of cinnamic acid; while the benzoresinol and the resinotannol can be employed in making picric acid.
Penang benzoin contains about 10 per cent. ligneous matter, much benzoic acid, and little or no cinnamic acid.
Palembang benzoin contains 7 to 8 per cent. of impurities, benzoic acid, and no cinnamic acid.
Benzoin has a peculiar fragrant odour, and is slightly heavier than water; its specific gravity being about 1.092 to 1.145. It melts at a gentle heat and gives off wbite vapours of benzoic acid with a small quantity of volatile oil. Alcohol dissolves most of it, ether rather less, but turpentine and petroleum spirit dissolve very little. Treated with sulphuric acid, benzoin or an alcoholic solution turn bright red, while with ferric chloride a green colour is produced.
Benzoin finds a small use in varnishes, chiefly on account of the odour which it imparts to the varnish; it is also used in making perfumes, incense, &c.
3rd. GUMS.-The true gums, such as gum arabic (the type of a true gum), gum tragacanth, and a few others are, like the resins,
exudations from trees, and are collected much in the same manner. They differ from resins in one or two important particulars. In the first place, they are more or less soluble in water; some, like arabic or acacia gums, are completely soluble ; others, like gum ghatti, are partially soluble; while others again, like tragacanth, are not properly dissolved by water, although acted upon by that vehicle. The true resins are quite insoluble in water. On the other hand, the gums are quite insoluble in alcohol and other similar solvents.
The gums, which belong to the third group of varnish materials, are almost exelusively used for making water varnishes, or (as in water-colour painting and in some kinds of distemper work) as fixing agents to fasten the pigment on to the work.
Besides the gums proper there are used in making water varnishes gelatine or glue, dextrine or British gum and albumen.
Gum Arabic.—The name of this gum is a misnomer, because it would indicate that it comes from Arabia, whereas but little, if any, now comes from that country; probably in early times it may
have been obtained from that country, or, at least, imported through it and hence the term “arabic" arose. It is also known as gum acacia, from the trees which yield it; but gum arabic, despite its error, is the name by which it is best known in the trade, and therefore it will be retained here.
The species of Acacia are profusely distributed throughout the tropical parts of Africa, Asia, and Australia, and are all gumproducers. The gums vary a little in appearance and properties, but all are more or less soluble in water, and give with that solvent a strongly adhesive mucilage useful for a great variety of purposes. These gums are distinguished in the trade by terms descriptive either of their place of origin or of their quality, such as picked Turkey, white Sennaar, Senegal, Cape, Mogador, Indian, Ghatti, Wattle, brown Barbary, &c. It is not necessary to enter into a very full description of all the varieties of gum arabic, as these are of little importance in connection with the topics dealt with in this book
Picked Turkey or white Sennaar arabic is the produce of Acacia Senegal, a tree growing in the Upper Nile regions and in Kordofan, where it is collected by the natives and shipped to Egyptian ports for exportation. Gum Senegal is the produce of the same species of Acacia, and is collected in the French province of Senegal. This variety of gum is very varied in quality, ranging from a fine white gum to a dark somewhat reddish gum. It is exported from Senegal almost entirely to Bordeaux, and but little comes into England. The best qualities are used for pharmaceutical,
confectionery, and other purposes, while the common qualities find a use in textile industries, varnish-making, and for making mucilages. Suakim or Soudan gum is a variety of gam arabic derived from two other species of Acacia, A. stenocarpa, the talch or talha tree of the Arabs, and A. Seyal, the soffar tree of the natives. This variety is collected in the Upper Nile regions and in the districts through which some of its tributaries flow. It is sent into commerce either through Khartoum, or, more largely, through Suakim, a port on the Red Sea. Very large quantities of this gum come into the English market, and it forms the main source of the gum arabic used for general commercial purposes. Its quality varies somewhat, from a good fine white gum to a dark discoloured sort. Morocco gum arabic is said to come from Acacia gummifera, but its source is somewhat uncertain. It is only collected in small quantities, and is chiefly exported through Mogador. It occurs in large globular tears of a brownish tint, from which circumstance it is sometimes known as brown Barbary gum. Cape gum.-The doornboom, Acacia horrida, one of the commonest trees of South Africa, yields a large quantity of a brownish gum, which differs from gum arabic in not being so completely soluble in water. It is used in the Cape Colony and surrounding districts in place of gum arabic, and is exported to a small extent. East Indian gum.-Much of what is sold as East Indian gum arabic is African produce, exported by way of Aden and Bombay, and does not differ, therefore, from Suakim gum in quality. Several species of Acacia grow in India and yield gum, which is collected and used locally, but a little finds its way into this country. Not much is known about these Indian gums. The Acacia arabica grows in Bengal, the Deccan, and Coromandel. The Acacia catechu, the cutch tree, yields a gum of rather dark colour, but otherwise equal to gum arabic in quality. Acacia speciosa yields a gum, known in India as the siris gum, which is of good quality. From other Indian Acacias gums are obtained in smaller quantities. Besides the Acacias other trees yield gums which sometimes find their way into the English market, such, for example, as gum ghatti; these gums are not so good as true gum arabic. The gums from the Australian wattles (which are various species of Acacia, the principal tree being the green wattle) A. decurrens, A. pycnantha, A. homalophylla, A. harpophylla, and A. Bidwilli, are of smaller importance. The quantity of gum obtained is rather larger than from African trees, and is of good quality.
The following description is nearly applicable to all the above varieties of gums. Gum arabic occurs in roundish or ovoid or