LABDANUM or LADANUM, is an unctuous resin, of an agreeable odour, found
besmearing the leaves and twigs of the _cystus creticus_, a plant which
grows in the island of Candia, and in Syria. It is naturally a
dark-brown soft substance, but it hardens on keeping. Its specific
gravity is 1·186. It has a bitter taste. Its chief use is in surgery for
making plasters.
LABRADORITE; opaline or Labradore felspar, is a beautiful mineral, with
brilliant changing colours, blue, red, and green, &c. Spec. grav. 2·70
to 2·75. Scratches glass; affords no water by calcination; fusible at
the blow-pipe into a frothy bead; soluble in muriatic acid; solution
affords a copious precipitate with oxalate of ammonia. Cleavages of
93-1/2° and 86-1/2°; one of which is brilliant and pearly. Its
constituents are, silica, 55·75; alumina, 26·5; lime, 11; soda, 4; oxide
of iron, 1·25; water, 0·5.
LABYRINTH, in metallurgy, means a series of canals distributed in the
sequel of a stamping-mill; through which canals a stream of water is
transmitted for suspending, carrying off, and depositing, at different
distances, the ground ores. See METALLURGY.
LAC, LAC-DYE. (_Laque_, Fr.; _Lack_, _Lackfarben_, Germ.) _Stick-lac_ is
produced by the puncture of a peculiar female insect, called _coccus
lacca_ or _ficus_, upon the branches of several plants; as the _ficus
religiosa_, the _ficus indica_, the _rhamnus jujuba_, the _croton
lacciferum_, and the _butea frondosa_, which grow in Siam, Assam, Pegu,
Bengal, and Malabar. The twig becomes thereby encrusted with a reddish
mammelated resin, having a crystalline-looking fracture.
The female lac insect is of the size of a louse; red, round, flat, with
12 abdominal circles, a bifurcated tail, antennæ, and 6 claws, half the
length of the body. The male is twice the above size, and has 4 wings;
there is one of them to 5000 females. In November or December the young
brood makes its escape from the eggs, lying beneath the dead body of the
mother; they crawl about a little way, and fasten themselves to the bark
of the shrubs. About this period the branches often swarm to such a
degree with this vermin, that they seem covered with a red dust; in this
case, they are apt to dry up, by being exhausted of their juices. Many
of these insects, however, become the prey of others, or are carried off
by the feet of birds, to which they attach themselves, and are
transplanted to other trees. They soon produce small nipple-like
incrustations upon the twigs, their bodies being apparently glued, by
means of a transparent liquor, which goes on increasing to the end of
March, so as to form a cellular texture. At this time, the animal
resembles a small oval bag, without life, of the size of cochineal. At
the commencement, a beautiful red liquor only is perceived, afterwards
eggs make their appearance; and in October or November, when the red
liquor gets exhausted, 20 or 30 young ones bore a hole through the back
of their mother, and come forth. The empty cells remain upon the
branches. These are composed of the milky juice of the plant, which
serves as nourishment to the insects, and which is afterwards
transformed or elaborated into the red colouring matter that is found
mixed with the resin, but in greater quantity in the bodies of the
insects, in their eggs, and still more copiously in the red liquor
secreted for feeding the young. After the brood escapes, the cells
contain much less colouring matter. On this account, the branches should
be broken off before this happens, and dried in the sun. In the East
Indies this operation is performed twice in the year; the first time in
March, the second in October. The twigs encrusted with the radiated
cellular substance, constitute the _stick-lac_ of commerce. It is of a
red colour more or less deep, nearly transparent, and hard, with a
brilliant conchoidal fracture. The stick-lac of Siam is the best; a
piece of it presented to me by Mr. Rennie, of Fenchurch-street, having
an incrustation fully one quarter of an inch thick all round the twig.
The stick-lac of Assam ranks next; and, last, that of Bengal, in which
the resinous coat is scanty, thin, and irregular. According to the
analysis of Dr. John, stick-lac consists, in 120 parts, of
An odorous common resin 80·00
A resin insoluble in ether 20·00
Colouring matter analogous to that of cochineal 4·50
Bitter balsamic matter 3·00
Dun yellow extract 0·50
Acid of the stick-lac (laccic acid) 0·75
Fatty matter, like wax 3·00
Skins of the insects, and colouring matter 2·50
Salts 1·25
Earths 0·75
Loss 4·75
------
120·00
According to Franke, the constituents of stick-lac are, resin, 65·7;
substance of the lac, 28·3; colouring matter, 0·6.
_Seed-lac._--When the resinous concretion is taken off the twigs,
coarsely pounded, and triturated with water in a mortar, the greater
part of the colouring matter is dissolved, and the granular portion
which remains being dried in the sun, constitutes _seed-lac_. It
contains of course less colouring matter than the stick-lac, and is much
less soluble. John found in 100 parts of it, resin, 66·7; wax, 1·7;
matter of the lac, 16·7; bitter balsamic matter, 2·5; colouring matter,
3·9; dun yellow extract, 0·4; envelopes of insects, 2·1; laccic acid,
0·0; salts of potash and lime, 1·0; earths, 6·6; loss, 4·2.
In India the _seed-lac_ is put into oblong bags of cotton cloth, which
are held over a charcoal fire by a man at each end, and, as soon as it
begins to melt, the bag is twisted so as to strain the liquefied resin
through its substance, and to make it drop upon smooth stems of the
banyan tree (_musa paradisa_). In this way, the resin spreads into thin
plates, and constitutes the substance known in commerce by the name of
_shell-lac_.
The Pegu stick-lac, being very dark coloured, furnishes a shell-lac of a
corresponding deep hue, and therefore of inferior value. The palest and
finest shell-lac is brought from the northern _Circar_. It contains very
little colouring matter. A stick-lac of an intermediate kind comes from
the Mysore country, which yields a brilliant lac-dye and a good
shell-lac.
_Lac-dye_ is the watery infusion of the ground stick-lac, evaporated to
dryness, and formed into cakes about two inches square and half an inch
thick. Dr. John found it to consist of, colouring matter, 50; resin, 25;
and solid matter, composed of alumina, plaster, chalk, and sand, 22.
Dr. Macleod, of Madras, informs me that he prepared a very superior
lac-dye from stick-lac, by digesting it in the cold in a slightly
alkaline decoction of the dried leaves of the _Memecylon tinctorium_
(perhaps the _M. capitellatum_, from which the natives of Malabar and
Ceylon obtain a saffron-yellow dye). This solution being used along with
a mordant consisting of a saturated solution of tin in muriatic acid,
was found to dye woollen cloth of a very brilliant scarlet hue.
The cakes of _lac-dye_ imported from India, stamped with peculiar marks
to designate their different manufacturers, are now employed exclusively
in England for dyeing scarlet cloth, and are found to yield an equally
brilliant colour, and one less easily affected by perspiration than that
produced by cochineal. When the lac-dye was first introduced, sulphuric
acid was the solvent applied to the pulverized cakes, but as muriatic
acid has been found to answer so much better, it has entirely supplanted
it. A good _solvent_ (No. 1.) for this dye-stuff may be prepared by
dissolving 3 pounds of tin in 60 pounds of muriatic acid, of specific
gravity 1·19. The proper _mordant_ for the cloth is made by mixing 27
pounds of muriatic acid of sp. grav. 1·17, with 1-1/2 pounds of nitric
acid of 1·19; putting this mixture into a salt-glazed stone bottle, and
adding to it in small bits at a time, grain tin, till 4 pounds be
dissolved. This solution (No. 2.) may be used within twelve hours after
it is made, provided it has become cold and clear. For dyeing; three
quarters of a pint of the solvent No. 1. is to be poured upon each pound
of the pulverized lac-dye, and allowed to digest upon it for six hours.
The cloth before being subjected to the dye bath, must be scoured in the
mill with fullers’ earth. To dye 100 pounds of pelisse cloth, a tin
boiler of 300 gallons capacity should be filled nearly brimful with
water, and a fire kindled under it. Whenever the temperature rises to
150° Fahr., a handful of bran, and half a pint of the solution of tin
(No. 2.) are to be introduced. The froth, which rises as it approaches
ebullition, must be skimmed off; and when the liquor boils, 10-1/2
pounds of lac-dye, previously mixed with 7 pints of the solvent No. 1.,
and 3-1/2 pounds of solution of tin No. 2., must be poured in. An
instant afterwards, 10-1/2 pounds of tartar, and 4 pounds of ground
sumach, both tied up in a linen bag, are to be suspended in the boiling
bath for five minutes. The fire being now withdrawn, 20 gallons of cold
water, with 10-1/2 pints of solution of tin being poured into the bath,
the cloth is to be immersed in it, moved about rapidly during ten
minutes; the fire is to be then re-kindled, and the cloth winced more
slowly through the bath, which must be made to boil as quickly as
possible, and maintained at that pitch for an hour. The cloth is to be
next washed in the river; and lastly with water only, in the fulling
mill. The above proportions of the ingredients produce a brilliant
scarlet tint, with a slightly purple cast. If a more orange hue be
wanted, white Florence argal may be used, instead of tartar, and some
more sumach. Lac-dye may be substituted for cochineal in the
orange-scarlets; but for the more delicate pink shades, it does not
answer so well, as the lustre is apt to be impaired by the large
quantity of acid necessary to dissolve the colouring matter of the lac.
_Shell-lac_, by Mr. Hatchett’s analysis, consists of resin, 90·5;
colouring matter, 0·5; wax, 4·0; gluten, 2·8; loss, 1·8; in 100 parts.
The resin may be obtained pure by treating shell-lac with cold alcohol,
and filtering the solution in order to separate a yellow gray
pulverulent matter. When the alcohol is again distilled off, a brown,
translucent, hard, and brittle resin, of specific gravity 1·139,
remains. It melts into a viscid mass with heat, and diffuses an aromatic
odour. Anhydrous alcohol dissolves it in all proportions. According to
John, it consists of two resins, one of which dissolves readily in
alcohol, ether, the volatile and fat oils; while the other is little
soluble in cold alcohol, and is insoluble in ether and the volatile
oils. Unverdorben, however, has detected no less than four different
resins, and some other substances in shell-lac. Shell-lac dissolves with
ease in dilute muriatic and acetic acids; but not in concentrated
sulphuric acid. The resin of shell-lac has a great tendency to combine
with salifiable bases; as with caustic potash, which it deprives of its
alkaline taste.
This solution, which is of a dark red colour, dries into a brilliant,
transparent, reddish brown mass; which may be re-dissolved in both water
and alcohol. By passing chlorine in excess through the dark-coloured
alkaline solution, the lac-resin is precipitated in a colourless state.
When this precipitate is washed and dried, it forms, with alcohol, an
excellent pale-yellow varnish, especially with the addition of a little
turpentine and mastic.
With the aid of heat, shell-lac dissolves readily in a solution of
borax.
The substances which Unverdorben found in shell-lac are the following: