RES 
RES 
leadensis, a tree which grows in Arabia, es- 
pecially near Mecca. It is so much valued 
by the Turks that it is seldom or never im- 
ported into Europe. We are of course ig- 
norant of its composition. It is said to be at 
first turbid and white; and of a strong aroma- 
tic smell, and bitter, acrid* astringent taste; 
but by keeping, it beco mes limpid and thin, 
and its colour changes first to green, then to 
yellow, and at last it assumes the colour of ho- 
ney. 
9. Copaiva, or balsam nf errpaiva. This 
resin is obtained from the cop.tifera oil! ema- 
ils ; a tree which grows in South America, 
and some of the West Indian islands. The 
resinous juice exudes from incisions made in 
the trunk of the tree. The juice thus ob- 
tained is transparent, of a yellowish colour, 
an agreeable smell, a pungent taste, at iirst of 
the consistence of oil* but it gradually be- 
comes as thick as honey. It is a combination 
of volatile oil and resin ; the oil is easily ob- 
tained by distillation with water. It is em- 
ployed in medicine. 
10. Dragon's blood. This resin is obtain- 
ed from different plants, as the calamus ro- 
tang, dracama draco, and pterocarpus draco. 
It comes both from the East Indies and Spa- 
nish America; and it cannot be doubted that 
different vegetable substances have been con- 
founded under the same name, the red colour 
having been formerly considered as sufficient 
to constitute dragon’s blood. The substance 
of that name described by French writers has 
an astringent taste, and is partly soluble in 
water. This seems to be the dragon’s blood 
of America, in which Proust detected abund- 
ance of tan. The dragon’s blood which 
comes to this country from the East Indies is 
tasteless, and insoluble in water ; but it dis- 
solves in alcohol, which it tinges of a fine 
crimson. It dissolves also in fixed oils, 
tinging them red. It is in small masses 
wrapt in leaves. Colour dark red. Powder 
crimson, Brittle. Fracture glassy. Opaque. 
Melts when heated, and readily burns. These 
properties prove it to be a resin. We must, 
then, distinguish two distinct substances hi- 
therto confounded under the same name. 
According to Brisson, the specific gravity of 
dragon’s blood (probably the species which 
contains tan) is 1.204. 
1 1 . Guniac. This resin is obtained from 
the guaiacum officinale, a treee which is a 
native of the West Indies. The resin exudes 
spontaneously, and is driven out melted by 
heating one end of the wood in billets previ- 
ously bored longitudinally ; the melted resin 
runs out at the extremity farthest from the 
fire. Guaiac is of a green colour, has some 
transparency, and is brittle. Its fracture is vi- 
treous. AVhen heated, it melts. It has no 
smell, and scarcely any taste. Alcohol dis- 
solves it ; but water has no effect upon it. 
When thrown on burning coals,, it diffuses a 
fragrant odour. When swallowed in powder, 
it causes a burning sensation in the throat. 
12. Botany Bay resin. This resin is said 
to be the produce of the acarois resinifera ; a 
tree which grows abundantly in New Holland, 
especially near Botanv Bay. Specimens of it 
were brought to London about the year 1 799, 
where it was tried as a medicine. Some ac- 
count was given of it in governor Philips’s 
Voyage, and in White’s Journal of a Voyage 
to New South Wales; but it is to professor 
Lichtenstein that we are indebted for an ac- 
count of its chemical properties. The resin 
exudes spontaneously from the trunk of the 
singular tree which yields it, especially if the 
bark is wounded. It is at first fluid, but be- 
comes gradually solid when dried in the sun. 
According to governor Philips, it is collect- 
ed usually in the soil which surrounds the 
tree, having doubtless run down spontane- 
ously to the ground. It consists of pieces of 
various sizes, of a yellow colour unless when 
covered with a greenish-grey crust. It is 
firm, yet brittle; and when pounded, does 
not stick to the mortar nor cake. In the 
mouth it is easily reduced to powder without 
Ticking to the teeth. It communicates merely 
a slight sweetish astringent taste. When mo- 
derately heated, it melts ; on hot coals it 
burns to a roal, emitting a white smoke which 
has a fragrant odour something like storax. 
When thrown into the fire, it increases the 
flame like pitch. It communicates to water 
the flavour of storax, but is insoluble in that 
liquid. When digested in alcohol, two-thirds 
dissolve : the remaining third consists of one 
part of extractive matter, soluble in water, 
and having an astringent taste; and two parts 
of woody fibre and other impurities, per- 
fectly tasteless and insoluble. The solution 
has a brown colour, and exhibits the appear- 
ance and the smell of a solution of benzoin. 
Water throws it down unaltered. W T hen 
distilled, the products were water, an empy- 
reumatic oil, and charcoal ; but it gives no 
traces of any acid, alkali, or salt, even 
when distilled with water. 
Twelve parts were boiled in a solution of 
pure soda in water. Two parts of the resin 
were dissolved ; the .remaining ten parts were 
floating on the solution, cohering together in 
clots. No crystals were obtained by evapo- 
rating part of the solution ; and when sulphu- 
ric acid was dropt into another portion, resin 
separated unaltered. When mixed with 
twice its weight of nitric acid, the resin swims 
unaltered on the surface ; but when heat is 
applied, a considerable effervescence takes 
place. The digestion was continued till the 
effervescence stopped, and the resin swam on 
the surface of the liquid, collected together in 
clots. It was then separated by filtration. It 
had lost T-th of its weight. The resin thus 
treated had acquired a bitterish taste, was not 
so easily melted as before, and alcohol was 
capable of dissolving only one-half of it. The 
solution was brown, tasted like bitter al- 
monds ; and when mixed with water, let fall 
a yellow resinous precipitate of a very bitter 
taste. The insoluble portion mixed with 
water, but formed a turbid liquid, which 
passed through the filtre. The nitric acid so- 
lution separated from the resin by filtration, 
was transparent ; its colour was yellow ; its 
taste bitter; and it tinged substances dipped 
into it of a yellow colour. By evaporation it 
yielded oxalic acid, and deposited a yellow 
earthy-like powder. This last substance was 
insoluble in water, and scarcely soluble in al- 
cohol. Its taste was exquisitely bitter, like 
quassia. It mixed with the saliva, and rea- 
dily stained the skin and paper yellow. The 
residuum continued bitter and yellow, but 
yielded no precipitate with potass and nitrat 
of lime.. The bitter substance, into which 
this resin was thus converted by nitric acid, 
deserves particular attention. He suspects 
that it is capable of producing the same 
RES 5C>7 
changes on all the resins: but this conjecture 
has been verified only with regard to colu- 
phonium, which lie found to yield equally a 
yellow bitter substance. 
13. The green resin which constitutes the 
colouring matter of the leaves of trees, and 
almost all vegetables, is insoluble in water, * 
and soluble in alcohol. From the experi- 
ments of Proust we learn, that when treated 
with oxy muriatic acid it assumes the colour ot 
a withered leaf, and acquires the resinous pro- 
perties in greater perfection. 
14. Copal. This substance, which de- 
serves particular attention from its importance 
as a varnish, and which at first sight seems to 
belong to a distinct class from the resin, is 
obtained from the rims copal linum, a tree 
which is a native of North America ; but the 
best sort of copal is said to come from Spa- 
nish America- Copal is a beautiful trans- 
parent resinous-like substance, with a slight 
tinge of brown. When heated it melts like 
other resins; but it differs from them in not 
being soluble in alcohol, nor in oil of turpen- 
tine without peculiar management. Neither 
does it dissolve in the fixed oils with the same 
ease as the other resins. It resembles gum 
anim6 exactly in appearance ; but is easily 
distinguished by the solubility of this last in 
alcohol. The specific gravity of copal va- 
ries^ 
RESISTANCE, or resist ins-force, in phi- 
losophy, denotes, in general, any power 
which acts in an opposite direction to another, 
so as to destroy or diminish its effect. 
There are various kinds of resistance aris- 
ing from the various natures and properties 
of the resisting bodies, and governed by vari- 
ous laws ; as, the resistance of solids, the re- 
sistance of fluids, the resistance ot the air, 
&e. 
Resistance of solids, in mechanics, is 
the force with which the quiescent parts of 
solid bodies oppose the motion of others con- 
tiguous to them. 
Of these there are two kinds : The first 
where the resisting and the resisted parts, i.e. 
the moving and quiescent bodies, are only 
contiguous, and do not cohere ; constituting 
separate bodies or masses. This resistance 
is what Leibnitz calls resistance of the sur- 
face, but which is more properly called fric- 
tion ; for the laws of which, see . the article 
Friction.' 
The second case of resistance, is where 
the resisting and. resisted parts are not only 
contiguous, but cohere,- being parts of the 
same continued body or mass. This resist- 
ance was first considered by Galileo, and 
may properly be called renitency. % . 
Theory of the resistance, of the fibres of 
solid bodies. To conceive an idea of this 
^resistance, or tendency. of .the parts, suppose 
a. cylindrical body suspended vertically by 
one end. • Here all its parts, being heavy, 
tend downwards, and endeavour to separate 
the two contiguous planes or surfaces where 
the body is the weakest; but all the parts of 
them resist this separation by the force with 
which they cohere, or are bound together. 
Here then are two opposite powers, viz. 
the weight of the cylinder, which tends to 
break it ; and the force of cohesion of the 
parts, which resists the fracture. 
If now the base of the cylinder is increased 
without increajiqg its length, it is evident 
