1 } 0T 
P 0 I 
4/2 p O I 
Point 'is also an iron or steel irtstrdmelit, 
used with some variety in several arts. En- 
gravers, etchers, cutters in wood, ike. use 
points to trace their designs on the copper, 
wood, stone, &c. See Engraving, &c. 
Point, in the manufactories, is a general 
term, used for all kinds of laces wrought with 
the needle; such are the point de Venice, 
point de France, point de Genoa, &c. which 
are distinguished by the particular economy 
and arrangement of their points. 
Point-Blank, in gunnery, denotes the 
shot of a gun levelled horizontally. 
POINTING the cable, in the sea-lan- 
guage, is untwisting it at the end, lessening 
the yarn, twisting if again, and making all 
fast with a piece of marline, to keep it from 
ravel ing out. 
POISONS. Poisons are commonly di- 
vided into the animal, vegetable, and mineral 
kinds. 
f. Poisons, animal. Several animals 
are furnished with liquid juices of a poison- 
ous nature, which when poured into fresh 
wounds, occasion the disease or death of the 
wounded animal. Serpents, bees, scorpions, 
Hud spiders, are well-known examples of such 
animals. The chemical properties of these 
poisonous juices deserve peculiar attention ; 
because it is only from such an investigation 
that we can hope to explain the fatal changes 
which they induce on the animal economy, 
or to discover an antidote sufficiently power- 
ful to counteract their baneful influence. 
Unfortunately the task is difficult, and per- 
haps surpasses oftr chemical powers. For 
the progress already made in the investiga- 
tion, we are indebted almost entirely to the 
labours of Fontana. 
1 . The poison of the viper is a yellow 
liquid, which lodges in two small vesicles in 
the animal’s mouth. These communicate by 
a. tube with the crooked fangs, which are hol- 
low, and terminate in a small cavity. When 
the animal bites, the vesicles are squeezed, 
and the poison forced through the fangs into 
the wound. This structure was partly ob- 
served by Fedi, an Italian philosopher ; and 
his discoveries were completed and confirmed 
by the experiments and observations of Fran- 
cini, Tysson, Mead, and Fontana. 
This poisonous juice occasions the fatal 
effects of the viper’s bite. If the vesicles are 
extracted, or the liquid is prevented from 
flowing into the wound, the bite is harmless. 
If it is infused into wounds made by sharp in- 
struments, it proves as fatal as when intro- 
duced by the viper itself. Some of the pro- 
perties of this liquid were pointed out by 
Mead; but it was Fontana who first subjected 
it to a chemical examination, sacrificing 
many hundred vipers to his experiments. 
The quantity contained in a single vesicle 
scarcely exceeds a drop. 
It has a yellow colour, has no taste; but 
when applied to the tongue, occasions numb- 
ness. It has the appearance of oil before the 
microscope, but it unites readily with water. 
It produces no change on vegetable blues. 
When exposed to the air, the watery part 
gradually evaporates, and a yellowish-brown 
substance remains, which has the appearance 
of gum arabic. In this state it feels viscid, 
like gum, between the teeth ; it dissolves 
readily in water, but not in alcohol ; and a - 
to hoi throws it down in a white powder from 
water. Neither acids nor alkalies have much 
effect upon it. It does not unite with vola- 
tile oils, nor sulphuret of potass. When 
heated, it does not melt, but swells, and does 
not inflame till it has become black. These 
properties are similar to the properties of 
gum, and indicate the gummy nature of this 
poisonous substance. Fontana made a set of 
experiments on the dry poison of the viper, 
and a similar set on gum arabic, and obtained 
the same results. 
From the late observations of Dr. Bussel, 
there is reason to believe that the poisonous 
juices of the other serpents are similar in their 
properties to those of the viper. 
This striking resemblance between gums 
and the poison of the viper, two substances of 
so opposite a nature in their effects upon the 
living body, is a humiliating proof of the 
small progress we have made in the chemical 
knowledge of these intricate substances. The 
poison of the viper, and of serpents in gene- 
nal, is most hurtful when mixed with the 
blood. Taken into the stomach, it kills if the 
quantity is considerable. Fontana has ascer- 
tained that its fatal effects are proportional 
to its quantity, compared with the quantity 
of the blood. lienee the danger diminishes 
as the size of the animal increases. Small 
birds and quadrupeds die immediately when 
they are bitten by a viper; but to a full-sized 
man the bite seldom proves fatal. 
Ammonia has been proposed as an anti- 
dote to the bite of the viper. It was intro- 
duced in consequence of the theory of Dr. 
Mead, that the poison was of an acid nature. 
The numerous trials of that medicine by Fon- 
tana robbed it of all its celebrity ; but it has 
been lately revived and recommended by 
Dr. Bamsay as a certain cure ior the bite of 
the rattlesnake. 
2. The venom of the bee and the wasp is 
also a liquid contained in a small vesicle, 
forced through the lioliow tube of the sting 
into the wound inflicted by that instrument. 
From the experiments of Fontana, we learn 
that it bears a striking resemblance to the 
poison of the viper. '1 hat of the bee* is much 
longer in drying when exposed to the air than 
the venom of the wasp. 
3. The poison of the scorpion resembles 
that of the viper also ; but its taste is hot 
and acrid, which is the case also with the ve- 
nom of the bee and the wasp. 
4. No experiments upon which w’e can re- 
ly have been made upon the poison of the 
spider tribe. From the rapidity with which 
these animals destroy their prey, and even 
one another, we cannot doubt that their poi- 
soirtfc sufficiently virulent. 
If. Poisons, vegetable, seem in general to 
prove fatal from an eyeess of narcotic matter ; 
but this is a subject which requires still farther 
examination. See Narcotic principle. 
III. Poisons, mineral. In general these 
substances, as arsenic and corrosive mercury, 
seem to attack the solid parts of the stomach, 
and to produce death by eroding its sub- 
stance ; but the antimonials seem rather to 
attack the nerves, and to kill by throwing the 
whole system into convulsions. 
Poison of copper. This metal, though 
when in an undissolved state it produces no 
sensible effects, becomes exceedingly active 
j when dissolved ; and such is the facility with 
; which the solution is effected, that it becomes 
a matter of some consequence to prevent the 
metal from being taken into the human body 
even in its proper form. It does not, how- 
ever, appear that the poison of copper is 
equally pernicious with those of arsenic or 
lead. The reason of this is, that it excites 
vomiting so speedily as to be expelled, even 
though taken in considerable quantity, before 
it has time to corrode the. stomach. Blue 
vitriol, which is a solution of copper in the 
vitriolic acid, has been used as a medicine in 
some diseases with great success. Verdigris 
also, which is another very active preparation 
of the metal, has been by some physicians 
prescribed as an emetic, especially in cases 
where other poisons had been swallowed, in 
order to procure -the most speedy evacuation 
of them by vomit. Where copper is not used 
with this view, it has been employed as a to- 
nic and antispasmodic, with which view it is 
admitted into the Edinburgh Dispensatory 
under the title of cuprum ammoniacale. The 
effects of the metal, however, when taken in 
a pretty large quantity, and in a dissolved 
state, or when the stomach abounds with acid 
juices sufficient to dissolve it, are very disa- 
greeable, and even dangerous ; as it occasions 
violent vomitings, pains in the stomach, faint- 
ings, and sometimes convulsions and death. 
T he only cure for these symptoms is, to expel 
the poison by vomiting as soon as possible, 
and to obtund its acrimony ; for which pur- 
pose drinking warm milk will probably be 
found the most efficacious remedy. In or- 
der to prevent the entrance of the poison into 
the body, no copper vessels should be used in 
preparing food but such as are either well 
tinned, or kepi ex eedingly clean. The 
practice .. gi . . g a fine blue or green colour 
| to pickier by prt paii.-g them in copper ves- 
sel-, ought not to be tolerated; tor Dr. Fal- 
coner, in a tr -:atise on this subject, assures us, 
| that Hr se are sometimes so strongly impreg- 
nated by this method of preparing them, that 
a small quantity of them will produce nausea. 
Mortars of brass or bell-metal ought, for the 
same reason, to be avoided ; as by this means 
a considerable quantity of the pernicious me- 
tal may be mixed with our food, or with me- 
dicines. In other cases, an equal caution 
ought to be used. The custom of keeping 
pins in the mouth, of giving copper halfpence 
to children to play with, &c. ought to be 
avoided ; as thus a quantity of the metal ■ 
may be insensibly taken into the body, after 
which its effects must be uncertain. It is pro- 
per to observe, however, that copper is much 
more easily dissolved when cold than when 
hot ; and therefore the greatest care should 
be taken never to let any thing designed for 
food, even common water, remain long in 
copper vessels when cold ; for it is observed, 
that though the confectioners can safely pre- 
pare the most acid syrups in clean copper ves- 
sels without their receiving any detriment 
whilst hot, yet if the same syrups are allowed 
to remain in the vessels till quite cold, they 
become impregnated with the pernicious qua- 
lities of the metal. 
Poison of lead. This metal, when taken 
slowly into the stomach with our food, is ca- 
pable of producing the disease usually called 
Devonshire colic, which, after a length of 
time, is succeeded by palsy. Dr. Flotilston, 
in his Essay on Poisons, has given a remark- 
able instance of a whole family who, having 
successively fallen a prey to" paralytic dis- 
