322 ' C H E M 
if the matters to he dyed are foaked in a folution of mu- 
riatoftin, inftead of alum-water. But the heft precau- 
tion for fixing the extractive colour upon ftuffs, is to 
let them foak for fome time in oxygenated muriatic acid, 
and then to plunge them into a folution of extraCf. Ex¬ 
tracts diftilled with a naked fire give an acid produCl; 
but it contains much more ammoniac than when they 
are-diftilled in the humid way, with lime or an alkali. 
Extracts diffolved in water, and left to themfelves with 
an accefs of air, walte away entirely: nothing is found 
remaining in the water but carbonats of potafti, of am¬ 
moniac, of lime, and fome other mineral falts, which 
exifted in the extraCl before, and cannot be deftroyed 
by putrid fermentation. Several extracts are prepared 
in commerce by means of water, as liquorice,’ caout- 
chou'k, &c. Extracts are ufed in medicine as aperitive, 
folvent, diuretic, ftomachic, remedies, and are daily ad- 
miniftered with great fuccefs. 
Of GUMS and MUCILAGES. 
The mucilaginous parts of the juice of plants, when 
dried, are called gums. There are three kinds, x. Gum 
Arabic, which flows from the acacia-tree in Egypt and 
Arabia. 2. The gum of our own country, which flows 
from the apricot, pear, and plum, trees, &c. 3. Gum 
tragacanth, which flows from the adragant of Crete, 
ciJlrUgalus tragacanth a. 
Gum is foluble in water, to which it gives a vifcous 
confiflence. This folution is called mucilage ; and by eva¬ 
poration becomes dry, tra-nfparent, and friable. The 
roots of mallows, the greater comfrey, the bark of elm, 
linfeed, the feed of quinces, &c. afford vifcous fluids, 
by maceration in water, which, by evaporation, leave 
true gums. The decoCtion of tbefe plants is fubftituted, 
in medicine, inftead of gums. The mucilages are infipid, 
foluble in water, but not in alcohol; coagulate with the 
addition of weak acids ; are carbonated by fire without 
yielding any fenfible flame ; exhale a confiderable quan¬ 
tity of carbonic acid by combuftion 5 and take the acid 
fermentation when weakened with water. 
Gum, by diftillation, affords piuch water and pyro- 
rmicous acid, a fmall quantity of thick and brown oil, 
And carbonic acid gas, mixed with hydrogen gas. Its 
coal is very bulky, and contains a fmall quantity of the 
carbonaj: of potalh. Treated with the nitric acid, the 
product is mucous or faccho-laftic acid, acetous acid, 
and laftly oxalic acid. Take any one of the gums men¬ 
tioned before : reduce it to powder, which put into a 
glafs retort; pour over it fix times its weight of acid at 
35 0 , adapt a receiver, and diftil with a gentle he?it. It is 
eafy to diftinguifh the different acids which are obtained. 
The acetous acid is known by its fmell; but care muft 
be taken to obferve the moment of its formation ; the 
mucous acid is precipitated in powder; and the oxalic 
acid always cryltallizes in cooling. 
Of SUGAR. 
Sugar has fome refemblance to gum. The faccharine 
quality is abundant in many vegetables, and generally 
accompanies gums. We cannot here enter into detail 
upon the extracting and refining of fugar. Sugar is dif- 
tinguifhed into raw fugar, mufcovado, brown fugar, 
white fugar, See. That part of the fugar which is inca¬ 
pable of becoming concrete, is called either coarfe fyrup, 
fine fyrup, or molaffes. 
Sugar is a lubftance holding in fome refpeCfs an inter¬ 
mediate place between effential falts and mucilages. It 
poffefl'es the property of cryltallizing. It cryltallizes in 
hexahedral truncated prifms, and in this ftate is called 
fugar-candy. By diftillation it affords water, pyro-mu- 
cous acid, and fome drops of empyreumatic oil; at the 
fame time that a great quantity of carbonic acid gas, and 
hydrogen gas, holding charcoal in folution, are difen- 
gaged. The refidue is a fpongy light coal, which con- 
I S T R Y. 
tains a fmall quantity of carbonat of potalh. Sugar is 
inflammable. On hot coals it melts, and. fwells up very 
much, emits a penetrating vapour, and becomes convert¬ 
ed into a brown yellow matter, called caramel. It flight- 
ly attraCls the moifture of the air, and is very foluble 
in water, to which it gives much confidence, and confti- 
tutes a kind of faccharine mucilage, called fyrup. Syrup, 
diluted with water, is capable of fermentation, and affords 
ardent fpirit. 
Sugar is very extenfively ufeful. It is a food which, 
taken in too large a quantity, is capable of heating the 
animal fyftem. It is very much ufed in pharmacy, where 
it is the bafe of lyrups, conferves, and other preparations. 
It is.very ufeful, as a medium to favour the folution or 
fufpenfion of refins, oils, &c. in water. It preferves the 
juices of fruits, after they are reduced into a jelly. It may 
even be confidered as a medicine, fince it is incilive, ape¬ 
rient, flightly tonic, and ftimulant; and there are, ac¬ 
cordingly, inftances of diforders, ariling from obltruc- 
tions, wliich have been cured by the habitual ufe of fugar. 
Of VEGETABLE ACIDS. 
The fourth immediate principle of vegetables, is what 
the firft chemifts called, in general, effential falts of ve¬ 
getables ; but we now give that name only to fucli as are 
fufeeptible of cryftallizatiom Chemifts formerly pre¬ 
tended that all effential lalts were the fame, being nothing 
but tartar or vinegar. Such was the ftate of the fcience, 
when Scheele difcovered that the citric, malic, and gallic, 
acids, were very different from the tartarous and acetous 
acids. It has been already remarked, that the juices of 
fome vegetables afforded the principles of mineral falts: 
the falts moft commonly prefent are, the fulphat and ni- 
trat of potalh, the muriat of foda, See.' 
The ancient chemifts held, that nitre was formed in 
the vegetables during their vegetation ; the moderns, on 
the contrary, believe that it is formed in the earth, and 
communicated to the plant through the medium of its 
vefftfts. However this may be, the lalts are formed during 
the procels of vegetation ; for, by planting fun-flowers 
in earth well lixiviated, by analyiis of their juices nitrat 
of potalh will be found. 
Vegetable acids are all compofed of radicals, which 
are themfelves combined and united with oxygen : thefe 
radical fubftances are carbon, hydrogen, and oxygen. 
One grand mark of diftindtion between vegetable acids 
and mineral acids, is, that the firft are all reduced, by 
complete analyiis. All vegetable acids are convertible 
one into the other, which arifes from the different pro¬ 
portions of the conftituent principles ; but it muft be re¬ 
marked, that neither nature nor the chemifts can work 
retrograde; for, having produced oxalic acid, the citric 
or malic acids cannot be formed from this. 
There are five kinds of vegetable acids: 1. Vegetable 
acids, formed in the fame vegetables, and pure. a. Acids 
partly fatu rated with a bafe in vegetables. 3. Thole ob¬ 
tained by fire. 4. By fermentation. 5. By mineral acids. 
Of the acids completely formed in vegetables, and which 
are extrafted in a ftate of purity by very Ample proceffes, 
we may diftinguifli four Ipecies, the citric, gallic, ben¬ 
zoic, and malic ; to which Fourcroy thinks we may add 
the fuccinic, as that acid, he fays, poffeffes all the pro¬ 
perties of the reft. 
SUCCINIC ACID. ' 
To obtain this acid, reduce amber to grofs powder § 
put it into a retort with a receiver adapted ; place the 
apparatus in a fand-bath, and proceed to diftillation 
with a gentle graduabfire. A little winter is firft obtain¬ 
ed, wduch foon acquires acidity; and a concrete lub¬ 
ftance adheres to the neck of the retort; this is the fuc¬ 
cinic acid : laftly a thick brown oil paffes ever. 
The acid obtained by this firft diftillation is never 
pure, but always contains tome oil. The following is a 
very 
