230 
B L E 
B L I 
B L l 
spots of oil or animal grease ; but it lias been 
long 'known that a weak solution of potash 
will effectually remove stains of tiiat kind. 
“ When I had to repair prints so torn that 
they exhibited only sciaps pasted upon other 
paper, 1 was afraid of losing these f ragments 
in the liquid, because tiie paste became dis- 
solved. In such cases I inclosed the prints 
in a cylindric glass vessel, which 1 inverted 
on the waiter in which I had put the mixture 
proper for extricating the oxygenated mu- 
riatic. acid gas. This vapour, by filling the 
whole inside of the jar, acted upon the print, 
extracted the grease as well as ink-spots, 
and the fragments remained pasted to the 
paper.” 
Easy method of preparing the oxygenated 
muriatic acid . — To oxygenate the muriatic 
acid, nothing is necessary but to dilute it, 
and mix it in a very strong glass vessel with 
manangese, in such a manner that the mix- 
ture may not occupy the w'hole contents ot 
the _ glass. Air-bubbles are formed on the 
surface of the liquor; the empty space be- 
comes filled with a greenish vapour ; and at 
the end of some hours the acid may be 
farther diluted with water, and then used. 
It has an acid taste, because the whole is not 
saturated with oxygen ; but it possesses all 
the virtues of the oxygenated muriatic acid. 
This process may be followed when there is 
not time to set up an. apparatus for distilling, 
in order to procure the oxygenated acid. 
BLECHNUM, in botany, a genus of 
plants of the class of the cryptogamia liliees ; 
the fructifications of which are disposed in 
two parallel lines, approaching to the rib of 
the frond. There are six species, all foreign 
plants. 
BLEEDING. See Surgery. 
BLENDE, or Black Jack. This ore 
very usually accompanies sulplmret ot lead. 
It is common, but seldom in such quantities 
as to make it worth working. It occurs both 
in amorphous masses and crystallized. r lhe 
primitive f orm of its crystals is the rhomboidal 
dodecahedron. 'I lie figure ot its integrant 
particles is the tetrahedron. 
Colour yellow, brown, or black. Streak 
reddish, brownish, or grey. Lustre vitreous, 
or that of the diamond. Generally some- 
what transparent. Refraction single. Tex- 
ture foliated. Clivage six-fold. Hardness (3 
to 8. Scratches sulphat of barytes. Specific 
gravity 4.000 to 4.1665. Before the blow- 
pipe decrepitates, and gives out white flowers 
of zinc, but does not melt. Borax does not 
affect it. When breathed upon, loses its 
lustre, and recovers it very slowly. It is 
usually divided into three subspecies. 
1. Yellow blende. Colour commonly sul- 
phur yellow, often passing into olive green or 
brownish red. Powder pale yellow. Streak 
yellowish or reddish grey, not metallic. Lus- 
tre that of the diamond. Transparency 
usually 2, sometimes 4. Often phosphoresces 
when scraped or rubbed. According to 
Bergman, it is composed of 
64 zinc 
20 sulphur 
5 iron 
4 fluoric acid 
1 silica 
6 water 
100 . 
2. Brown blende. Colour different shades 
of brown. Surface often tarnished. Powder 
brownish grey. Streak yellowish grey. Lus- 
tre internal, Vitreous. Transparency 0 to 2, 
sometimes 4. A specimen of this variety, 
analysed by Bergman, contained 
44 zinc 
17 sulphur 
24 silica 
5 iron 
5 alumina 
5 water 
100 . 
3. Black blende. Colour black or brownish 
black ; surface often tarnished blue ; tips of the 
crystals often blood-red. Powder brownish, 
black. Streak reddish grey. Lustre inter- 
nal, that of the diamond. Transparency 
0 to 1 ; the red parts 2. Hardness 8. A spe- 
cimen of this variety, analysed by Bergman, 
contained 
52 zinc 
26 sulphur 
4 copper 
8 iron 
6 silica 
4 water 
100 . 
BLENNIUS, the Blenny, a genus of 
fishes belonging to the order of jugulares ; the 
characters of which are : the head slants or 
declines to one side; there are six rays in 
the membrane of the gills ; the body tapers 
towards the tail ; the belly fins have only two 
blunt bones; and the tail fin is distinct. The 
species are 13, among which are : 
1. Blennius cornutus, with a simple ray 
above the eyes, and a single back tin. 
2. Blennius* galena, with a transverse mem- 
braneous crest upon the head, is found in the 
European seas. 3. Blennius gattorugine (See 
Plate, Nat. Hist. fig. 47), with small palmated 
fins about the eye-brows and neck. It is about 
seven or eight inches long, and is found in 
the European seas. 4. Blennius ocellaris, 
with a furrow betwixt the eyes, and a large 
spot on the back fin. It is found in the Euro- 
pean seas. (See Plate, Nat. Hist. fig. 48). 
5. Blennius raninus, with six divisions in the 
belly fins, is found in the lakes ot Sweden. 
It is remarkable that when this fish appears 
in the lake, all the other fishes retire ; and 
what is worse, it is not fit for eating. 6. Blen- 
nius viviparus, has two tentacula at the 
mouth. They bring forth 200 or 300 young 
at a time. Their season of parturition is a 
little after the depth of winter. Before mid- 
summer they quit the bays and shores, and 
retire into t lie deep, where they are com- 
monly taken. They are a very coarse fish, 
and eaten only by the poor. T hey are com- 
mon in the mouth of the Esk, at Y\ hitby, 
Yorkshire, where they are taken frequently 
from off the bridge. 'They sometimes grow 
to the length of a foot. Their form is slender, 
and the backbone is as green as that of a sea- 
needle. See Plate, Nat. Hist. fig. 49). 
BLIGHT, in husbandry, a disease incident 
to plants, which affects them variously, the 
whole plant sometimes perishing by it, and 
sometimes only the leaves and blossoms, 
which will be scorched and shrivelled up, the 
nut remaining green and flourishing. Various 
causes have been assigned for this disease, 
and various cures proposed. It sometimes is 
in the plant itself from imperfect secretion, 
but is more commonly the eff ect of cold winds 
in the spring. See Plants. 
BLINDS, or Blindes, in the art of war, 
a sort of defence commonly made of oziers, 
or branches interwoven and laid across be- 
tween two rows of stakes, about the height of 
a man, and four or five feet asunder, used 
particularly at the heads of trenches when 
they are extended in front towards the glacis; 
serving to shelter the workmen, and prevent 
their being overlooked by the enemy. 
BLINDNESS, a total privation of sight, 
arising from an obstruction of the functions < 
of the organs of sight, or from an entire de- 
privation of them. 
The causes of blindness' are various ; pro- ; 
ceeding from cataracts, gutta serena’s, &c. 
There are also periodical blindness, as a de- 
fect of sight in some towards night, in others ] 
only in the day ; the former of which is j 
termed nyctalopia, the latter hemeralopia. 
It is said, that in several parts of Persia, j 
there are found vast numbers of blind people j 
of all ages, sexes, and conditions, occasioned 
by a species of little flies, which prick the j 
eyes and lips, and enter the nostrils, carrying j 
certain blindness with them when they fight j 
. on the eyes. 
If we consider blindness in a moral or 
philosophical view; as there is not any sense j 
or faculty of the corporeal frame which affords j 
so many* sources of utility and entertainment ■ 
as the power of vision ; so is there not any j 
privation which can be productive ot disad- 1 
vantages so various and so bitter as the want j 
of sight. By no avenue of corporeal per- j 
ception is knowledge, in her full extent, so ' 
accessible to the rational soul, as by the glo- 
rious and delightful medium of light. 'J o i 
the blind, on the contrary, the visible uni- 
verse is totally annihilated; he has not even 
any r distinct idea ot space, except that in j 
which he stands, or to which his extremities j 
can reach. Sound, indeed, gives him some! 
ideas of distant objects; but these ideas are! 
extremely obscure and indistinct. r l hey are j 
obscure because they consist alone of the ■ 
objects whose oscillations vibrate on his ear, 
and do not necessarily suppose any other! 
bodies with which the intermediate space may 
be occupied; they are indistinct, because! 
sounds themselves are frequently ambiguous, 
and do not uniformly indicate their real 
causes. And though by them the idea of 
distance in general, or even of some part icu- 
lar distances, may be obtained; yet they 
never fill the mind with those vast and exalt- 
ing ideas of extension which are inspired by 
ocular perception. For though a clap ofl 
thunder, or an explosion of ordnance, may 
be distinctly heard after the sound lias tra- 
versed an immense region of space, yet, 
when the distance is uncommonly great, it 
ceases to be indicated by sound ; and there- 
fore the ideas acquired by auricular experi- 
ments, of extension and' interval, are ex- 
tremely confused and inadequate. r i lie 
comprehensive eye darts its instantaneous 
glance oxer extensive valleys, lofty moun- 
tains, protracted rivers, illimitable oceans. 
It views in an instant the mighty space from 
earth to heaven, cn from one star to another. 
By the assistance of telescopes, its power is 
almost infinitely extended, its objects mul- 
tiplied, and the sphere of its observation im- 
mensely enlarged. Ihus the imagination, 
