' rsL 
cured with salt, that must be dissolved by 
steeping th'jm in water before they are pre- 
pared for isinglass ; the fresh sound must 
then be laid upon a block of wood, whose 
surface is a little elliptical, to the end of 
■which a small hair-brush is nailed, and with 
a saw knife the membranes on each side of 
the sound must be scraped off. The knife 
is rubbed upon the brush occasionally, to 
clear its teeth; the pockets are cut open 
with scissars, and perfectly cleansed of the 
mucous matter with a coarse cloth ; the 
sounds are afterwards w'ashed a few mi- 
nutes in lime-water in order to absorb their 
oily principle, and lastly in clear water. 
They are then laid upon nets to dry, but if 
intended to resemble the foreign isinglass, 
the sound of the cod will only admit of that 
called book, but those of ling both shapes. 
The thicker the sounds are tiie better the 
isinglass. 
ISIS, coral, in natural history, a genus of 
the Vermes Zoophyta class and order. Ani- 
mal growing in the form of a plant ; stem 
stony, jointed, the joints longitudinally 
striate, united by spongy or horny junctures, 
and covered by a soft porous cellular flesh 
or bark ; mouth beset -vi'ith oviparous po- 
lypes. There are six species. I. hippuris; 
with white striate joints and black junctures ; 
it is found chiefly in the Indian seas, grow- 
ing to rocks, and is from two inches to two 
feet long. I. entrocha ; stem testaceous, 
round, with orbicular perforated joints and 
verticillate dichotomous branches. Inha- 
bits the ocean. The stem is about the 
thickness of a finger, with crowdeU flat or- 
bicular joints perforated in the centre, the 
perforation is pentangular, with the disk 
substriate from the centre ; outer bark or 
flesh unequal, and surrounded with a row 
of tubercles ; branches thin, dichotomous, 
continued, not jointed. Hence it is thought 
that those fossils, called entrochi, are speci- 
mens of this species of coral. 
ISLAND, or Iceland, crystal, a body fa- 
mous among the writers of optics, for its pro- 
perty of a double refraction; but impro- 
perly called by that name, as it has none 
of the distinguishing characters of crystal, 
and is plainly a body of another class. Dr. 
Hill has reduced it to its proper class, and 
determined it to be of a genus of spars, 
which he has called, from their figure, pa- 
rallelopipedia, and of which he has de- 
scribed several species, all of which, as well 
as some other bodies of a different genus, 
have the same properties. Bartholine, 
Huygens, and Sir Isaac Newton, have de- 
ISO 
scribed the body at large, but have ac- 
counted it either a crystal or a talc ; errors 
which could not have happened, had the cri- 
terions of fossils been at that time fixed ; 
since Sir Isaac Newton has recorded its 
property of making an ebullition with aqua- 
fortis, which alone must prove that it is 
neither talc nor crystal, both those bodies 
being wholly unaffected by that menstruum, 
isee Crystal, Oryctology, and Talc. 
It is always found in form of an oblique 
paralielopiped, with six sides, and is found 
of various sizes, from a quarter of an inch to 
three inches or more in diameter. It is 
' pellucid, and not much less bright than 
the purest crystal, and its planes are all to- 
lerably smooth, though, when nicely viewed, 
they are found to be waved with crooked 
lines made by the edges of imperfect 
plates. 
What appears very singular in the struc- 
ture of this body, is, that all the surfaces 
are placed in the same manner, and conse- 
quently it will split off into thin plates, ei- 
ther horizontally or perpendicularly ; but 
this is found on a miscroscopic examination, 
to be owing to the regularity of figure, 
smoothness of surface, and nice joining of 
the severalsinall paralielopiped concretions, 
of which the whole is composed ; and to the 
same cause is probably owing its remark- 
able property in refraction. See Optics, 
and Refraction. 
It is very soft, and eatdly scratched with 
the point of a pin ; it w'ill not give fire on 
being struck against steel, and ferments 
and is perfectly dissolved in aquafortis. It 
is found in Iceldhd, from whence it has its 
name ; and in France, Germany, and many 
other places. In England fragments of 
other spars are very often mistaken for it, 
many of them having in some degree the 
same property. 
ISNARDIA, in botany, so named in 
memory of Mons. Antoine Danti dTsnard, 
member of the Academy of Sciences, a 
genus of tlie Tetrandria Monogynia class 
and order. Natural order of Calycan- 
them®. Salicari®, Jussieu. Essential cha- 
racter; calyx four- cleft ; corolla none; cap- 
sule four-celled, covered by the calyx. 
There is but one species, viz. I. palustris, 
which bears a great resemblance to peplis 
portulaca ; it is creeping and floating ; the 
flowers are axillary, opposite, sessile, and 
green. It is a native of Italy, France, 
Alsace, Russia, Jamaica, and Virginia, in 
rivers. 
ISOCHRONAL, Isochrone, or Iso- 
