1835. 1836. 1835. 1836.
1,814 cwts. | 1,735 cwts. | _£_4,290 | _£_4,125
ISLAND MOSS (_Lichen d’Islande_, Fr.; _Flechte Isl._, Germ.); is a
lichen, the _Cetraria islandica_, which contains a substance soluble in
hot water, but forming a jelly when it cools, styled _lichenine_ by M.
Guerin. Lichenine has a yellowish tint in the dry state, is transparent
in thin plates, insipid, inodorous, and difficult to pulverize. Cold
water makes it swell, but does not dissolve it. It is precipitated in
white flocks by alcohol and ether. Iodine tinges it of a brownish green.
Sulphuric acid converts it into sugar; and the nitric into oxalic acid.
Lichenine is prepared by extracting first of all from the plant a bitter
colouring matter, by digesting 1 pound of it in 16 pounds of cold water
containing 1 ounce of pearl-ash; then draining the lichen, edulcorating
with cold water, and boiling it in 9 pounds of boiling water, till 3
pounds be evaporated. The jelly which forms, upon cooling the filtered
solution, is dark coloured, but, being dried and redissolved in hot
water, it becomes clear and colourless. Lichenine consists of 39·33
carbon, 7·24 hydrogen, and 55·43 oxygen. With potash, lime, oxide of
lead, and tincture of galls, the habitudes of lichenine and starch are
the same. The mucilage of island moss is preferred in Germany to common
paste for dressing the warp of webs in the loom, because it remains
soft, from its hygrometric quality. It is also mixed with the pulp for
sizing paper in the vat.
IVORY (_Ivoire_, Fr.; _Elfenbein_, Germ.); is the osseous matter of the
tusks teeth of the elephant, the hippopotamus, or morse, wild boar,
several species of phocæ, as well as the horn or tooth of the narwhal.
Ivory is a white, fine-grained, dense substance, of considerable
elasticity, in thin plates, and more transparent than paper of equal
thickness. The outside of the tusk is covered by the cortical part,
which is softer and less compact than the interior substance, with the
exception of the brown plate that sometimes lines the interior cavity.
The hardest, toughest, whitest, and most translucent ivory, has the
preference in the market; and the tusks of the sea-horse are considered
to afford the best. In these, a rough glassy enamel covers the cortical
part, of such hardness, as to strike sparks with steel. The horn of the
narwhal is sometimes ten feet long, and consists of an ivory of the
finest description, as hard as that of the elephant, and susceptible of
a better polish; but it is not in general so much esteemed as the
latter.
Ivory has the same constituents as the teeth of animals, three-fourths
being phosphate, with a little carbonate of lime; one-fourth cartilage.
See BONES.
It is extensively employed by miniature painters for their tablets; by
turners, in making numberless useful and ornamental objects; by cutlers,
for the handles of knives and forks; by comb-makers; as also by
philosophical instrument makers, for constructing the scales of
thermometers, &c. The ivory of the sea-horse is preferred by dentists
for making artificial teeth; that of the East India elephant is better
than of the African. When it shows cracks or fissures in its substance,
and when a splinter broken off has a dull aspect, it is reckoned of
inferior value. Ivory is distinguishable from bone by its peculiar
semi-transparent rhombohedral net-work, which may be readily seen in
slips of ivory cut transversely.
Ivory is very apt to take a yellow-brown tint by exposure to air. It may
be whitened or bleached, by rubbing it first with pounded pumice-stone
and water, then placing it moist under a glass shade luted to the sole
at the bottom, and exposing it to sunshine. The sunbeams without the
shade would be apt to occasion fissures in the ivory. The moist rubbing
and exposure may be repeated several times.
For etching ivory, a ground made by the following recipe is to be
applied to the polished surface:--Take of pure white wax, and
transparent tears of mastick, each one ounce; asphalt, half an ounce.
The mastick and asphalt having been separately reduced to fine powder,
and the wax being melted in an earthenware vessel over the fire, the
mastick is to be first slowly strewed in and dissolved by stirring; and
then the asphalt in like manner. This compound is to be poured out into
lukewarm water, well kneaded, as it cools, by the hand, into rolls or
balls about one inch in diameter. These should be kept wrapped round
with taffety. If white rosin be substituted for the mastick, a cheaper
composition will be obtained, which answers nearly as well; 2 oz.
asphalt, 1 oz. rosin, 1/2 oz. white wax; being good proportions.
Callot’s etching ground for copper plates, is made by dissolving with
heat 4 oz. of mastick in 4 oz. of very fine linseed oil; filtering the
varnish through a rag, and bottling it for use.
Either of the two first grounds being applied to the ivory, the figured
design is to be traced through it in the usual way, a ledge of wax is to
be applied, and the surface is to be then covered with strong sulphuric
acid. The effect comes better out with the aid of a little heat; and by
replacing the acid, as it becomes dilute by absorption of moisture, with
concentrated oil of vitriol. Simple wax may be employed instead of the
copperplate engravers’ ground; and strong muriatic acid instead of
sulphuric. If an acid solution of silver or gold be used for etching,
the design will become purple or black, on exposure to sunshine. The wax
may be washed away with oil of turpentine. Acid nitrate of silver
affords the easiest means of tracing permanent black lines upon ivory.