234 C H E M I 
Oils which contain mucilage, extractive bodies, &c. 
are generally coloured: they may be purified by water 
only, which feizes on the mucilage, &c. The water (hould 
be ftrongly agitated.; or it may even be (lightly heated. 
If water be thrown on burning oil, it caufes it to give a 
ftronger flame, and a fudden detonation takes place, pro¬ 
ceeding from the decomposition ot the water, which af- 
fords oxygen to the oil, and allows much hydrogen gas 
to efcape ; tome carbonic acid is formed alfo. 
Sulphur unites with oil, forming fulphure of oil, or 
rubies of fulphur, or balfam of fulpbur. Boil fublimed 
fulphur with four times its weight of oil of olives,, till 
the folution has acquired a dark-red colour. When the 
oil is well (aturated, the fulphur will be obtained in a 
regular form, and is precipitated in cryltals by cooling. 
By diftilling this combination, fulphurated hydrogen gas 
•will be obtained. 
Oil diflblves phofphorus; by this means Pelletier ob¬ 
tained it in cryltals. It is fuppofed that fulphurated 
and carbonated hydrogen a6t upon oils alio. Charcoal 
has the property of clarifying or whitening oil; boil the 
•oil over charcoal; after a flight ebullition, pafs the oil 
through a cloth, or.filter it; the oil thus obtained is very 
clear, and makes no depofit. 
Fixed oils do not appear capable of uniting with pure 
metallic fubllances, excepting copper and iron, on which 
they have a conliderable action. But they combine with 
metallic oxyds., and form thick concrete combinations, 
of afoapy appearance, as may be obferved in the prepara¬ 
tion of unguents and plaifters. In docimaftic operations, 
fixed oils are ufed to reduce metallic oxyds. Berthollet 
defcribes an ingenious and Ample proceis for immediate¬ 
ly combining a fixed oil with any metallic oxyd, in the 
iaponaceous form. It conlifts in pouring a folution of 
foap into a metallic folution ; the acid of the latter feizes 
the fixed alkali of the foap, and the metallic oxyd is pre¬ 
cipitated in combination with the oil, to which it com¬ 
municates its colour. In this manner a beautiful green 
foap is formed with fulphat of copper, and a brown foap 
with fulphat of iron ; thefe compounds may perhaps be 
ufeful in painting. Scheele has difcovered, that by 
•combining oil of fweet almonds, of olives, of rape, or 
of linfeed, with half the quantity of the oxyd of lead, 
and adding a fmall quantity of water to the mixture, a 
fubftance is feparated, which he calls the fiveet principle. 
By evaporating the water, this principle is obtained, of 
the confidence of fyrup. By a ftrong heat it takes fire ; 
part is volatilized in the diflillation without burning ; 
the refidual coal is very light. The fweet principle does 
not cryftallize, nor does it appear fulceptible of fermen¬ 
tation ; nitric acid, diddled four times from it, produces 
oxalic acid. This principle appears to be a kind of 
mucilage. Scheele imagined that it might be decompo- 
ed by repeated diflillation. When the oil or fat is frefli, 
thefulphuric acid finds no appearance of the oxyd of lead, 
and the liquor does not grow thick. If the oil be dale and 
rancid, oxyd of lead is difcovered, which is precipitated by 
the fulphuricacid. Its diflillation requires the fame heat as 
,for the fulphuric acid; part of the lweet principle pafiesover 
undecompofed, in form of a thick fyrup, preserving 
its tafle; it then becomes empyreumatic ; then a brown 
oil rites.; and a light friable coal remains in the retort, 
which contains no lead. The fweet principle mixes with 
.alcohol, and is precipitated with it in the gelatinous form. 
The preparations called oinlinents or plaijfers, may be 
made by combining fixed oils with metallic oxyds. 
Take three parts of the l'emi-vitreous oxyd of lead, fix 
parts of oil of olives, and fix parts of water ; put thefe 
into a copper vefiel, over a fire which will keep up a mo¬ 
derate ebullition ; ftirthe mixture without ceafing, with 
a wooden fpatula, till the mafs becomes of a white colour, 
and has acquired the confidence of a foftilh ointment. 
Take care to add warm water from time to time, as that 
in the vefiel evaporates, that the ointment may never be 
dry. When the ointment is of a proper confidence, take 
S T R Y. 
the vefiel off the fire, let it cool, then pour the matter into 
cold water to form it. into a mafs. 
Acids a£t more readily upon fixed oils than do the me¬ 
tallic oxyds. Achard, Cornette, and Macquer, have 
made experiments refpefiting thefe compounds. Achard 
added concentrated fulphuric acid, by fmall portions, to 
fixed oil. This mixture, being continually triturated, be¬ 
comes at length converted into a brown mafs, foluble in 
water and alcohol. The concentrated fulphuric acid ren¬ 
ders fixed oils black, and caufes them to refemble bitu¬ 
mens. This phenomenon appears to arife from the re¬ 
action of the hydrogen of the oil on the oxygen of this- 
acid. 
Weak nitric acid a£ts upon oil by yielding a portion 
of its oxygen ; in which cafe the oil thickens, and takes 
the form of fat. But if the acid be concentrated, and 
aflifted by heat, then there is inflammation, particularly 
with the drying oils. The muriatic and carbonic acids 
aCt but weakly on fixed oils; the former, however, in a 
concentrated flate, combines with them to a certain de¬ 
gree, according to Cornette. The oxygenated muriatic 
acid thickens them much and appears, by the abforption 
of its oxygen, to convert them into a lubflance nearly re- 
fembling wax. This affinity of oil for oxygen occafions 
the aftion of oils in the revivification of metals. 
Barytes, lime, ftrontian, magneiia, and alkalis in ge¬ 
neral, unite with oils, and form what is called foap. The 
earthy foaps are eafily produced by the aftion of double 
affinity. For this purpofe, pour into a folution of foap a 
nitric folution of bar :es, lime, or ftrontian ; the acid 
unites with the alkali or the foap, and the earthy lubflance 
is precipitated with the oil. 
Soaps prepared with alkalis are more or lefs folid or 
hard; with potalh they are generally foft; thofe with 
foda are therefore preferred. To make the amygdaline 
foap, firft prepare lbme cauftic loda : Boil one part of 
good Alicant ioda.and two parts of quicklime, 1 in a fuf- 
ficient quantity of water, filtre the liquor through a 
cloth, and then evaporate, till a phial which would con¬ 
tain eight parts of clear water may contain eleven parts 
of this liquid, which is now called foap-lye. Mix in a 
glazed pan one part of this foap-lye with two parts of the 
oil of fweet almonds ; let this digeft in a heat that will 
juft keep it fimmering ; continue the coftion, ftirrjng it 
gently with a piece of wood, till, by dropping fome of 
the mixture on a fmoctli (tone, it appears that the foap 
coagulates, and that the water runs from it. Takeout 
the foap before it get's cold, and run it into moulds. 
This l'oap may be prepared alfo without heat, by mix¬ 
ing the oil and the foap-lye in the proportions belt fuited 
to the purpofe, which proportions cannot be exactly let 
down unlefs the alkali could be always at the fame point 
of concentration ; it mu ft therefore be added by degrees, 
till the matter becomes of a folid confidence, or rather till 
the combination is complete ; finiffi the operation by 
ftirring the mixture well, and then leave it to fettle in a 
cool place. In the arts, they ufe oil of olives, of nuts, 
of rape-ieed, fat, fifh-oil, and even animal fubllances, as 
wool, cuttings of cloth, &c. Chaptal prepared foap with 
fuch matters; we fliall lpeak of them when we come to 
treat of animal fubllances. 
Coloured foaps are made alfo; in which cafe the ma¬ 
terials are foda, fulphat of copper, cinnabar, &c. accord¬ 
ing to the colour required. In the union of oil with al¬ 
kali in the cold, there is a difengagement of caloric. In 
general the drying oils, or thofe of the fecond genus, do 
•not make fuch good foaps as thofe of the firft and third. 
What caufes the thickening of the foaps, is, firft the tem- 
peratuie; and fecondly becaule the alkalis have more af¬ 
finity with oil than they have with water; befid.es;this, 
there is an abforption of oxygen during ikponification, 
that is, the oil beqomes concrete by ablorbing oxygen. 
Soaps Ihould have a lweet or infipid talte. Soaps, if pro¬ 
perly made,are all foluble in water; the folution Is always 
thick and opaque, even when filtered. Diftilled in a re¬ 
torts 
