174 C H E M 
and bring back the wood to its original Hate, is im- 
poffible. This is therefofe what conltiLutes compound 
analyfis. 
Synthcfs, is that operation which ferves as a proof of 
the analyfis. Many fynihefes are made in analyfing a 
body ; for, if that body contains three or four 1'ubltances, 
two or three of them often unite while we are feparating 
the third or fourth. Ecfides, the order and proportion 
which enter into the competition of a body, give occa- 
fion to many iynthefes. By order is meant the nature of 
the bodies which combine ; and proportion is the quantity 
of the parts of each of the bodies which unite together. 
And this intimate and reciprocal a 51 jon of bodies upon 
each other is produced by attraction. 
Chemical attraction, is the principle of the intimate 
aftion of the molecules of the body, which we are to 
diftinguilh from the viral a£tiori. Mr. Kirwan, defines 
it to be, “ that power by which the invilible particles of 
different bodies intermix and unite with each other ib ill - 
timately, as to be inseparable by mere mechanical means. 
Tn this refpeftit differs from magnetic and ele£trical at- 
traftion. It alfo differs from the attraftion of cohefion 
in this, that the latter takes place betwixt particles of al¬ 
most all forts of bodies wholelhrfaces are brought into 
immediate contact with each other; for chemical attraction 
does not aft with that degree of indifference, but canfes a 
body already united to another, to quit that other and unite 
with a third; and hence it is called 'elective attraction.” 
This principle was well known in the earlielt times, but it 
was not attended to with fufiicient care, till experience had 
Ihown that its influence on the praftice, is equal to that on 
the theory, of the fcience we are treating of. It is this doc¬ 
trine that mult g.uide the praftitioner in the refearches 
neccffiry for the advancement of chemiftry, and muff 
be confulted by the philofopher who collefts and com¬ 
pares the fadts. It is the compafs. by which both muff 
tteer; and it may be truly affirmed, that he w r ho clofely 
inveftigates the chemical attractions, will fpeedily know 
every thing that the fublimell chemiftry has to offer. 
There are two kinds of chemical attraction: the mole¬ 
cular, or attfaftion of aggregation; and the atcraftion 
of compofition. The difference between tliefe two kinds 
of attraction, is, that aggregation gives always the lame 
body for the l'efult, becaule it confilts only in the fuc- 
cefiiveand conitant collection of fimiiar molecules. Hence 
where the attraction of aggregation tcafes, the aftion of 
compofition begins. The attraction of compofition, on 
the contrary, forms different bodies, according to the 
order and proportion in which the different molecules 
ox elementary particles are brought together. Thefe 
operations, as may be imagined, are infinite as to form, 
colour, and all other modifications. 
Examples of the At t raff ion of Aggregation. —Two drops 
of water, and two globules of mercury, occafion an ag¬ 
gregation; but nothing can thence arile but an increale 
of the mafs, without the nature of the fubftance under¬ 
going the lead: change. But here aggregation muft not 
Be confounded with colleffion : in the latter, the integral 
parts have no fenfible adhefion. Aggregation and col- 
leftion, again, muff be diftinguilhed from mixture: a 
mixture always contains conftituent parts of a different 
nature; as gun-powder; and, in general, all the phar¬ 
maceutical compound powders. There are alfo different 
forts of aggregates; hard or folid, foft, fluid, and gaieous. 
Solid, as wood, fulphur, &c. Soft, as pitch, the fat of 
meat, Sec. Liquid, as water, oil, alcolial, &c. Gafeous, 
as air, and the different vapours or Itearas. Aggregates 
are likewife divided into, irregular , as native ltone; re¬ 
gular, as cryltallized ftone; organical, as wood, and 
bone. Def ruffian of aggregation, denotes the mecha¬ 
nical means employed by analyfis to divide bodies. By 
kftening the aggregation, bodies prelent lets adhefion 
and more furface : thus is the aftion of chemical agents 
facilitated, and their energy increaied. 
Examples of the Attraction of Compofition. —Ten Laws, 
2 
S T R Y. 
eftabliflied by Fourcroy include all the , phenomena of 
the attraftion of compofition. 
I. It takes place only between different bodies. —To de- 
monftrate that two heterogeneous bodies aft mutually 
upon each other, by reciprocally giving out their parti¬ 
cular properties, put into a glafs a little potalh, or pow¬ 
dered marble, pour thereon lome nitric acid. The phe¬ 
nomenon which takes place, and the compofition which 
refults, prove, that thefe bodies, though heterogeneous, 
combine extremely well. 
II. It takes place Only between the leaf moleciilcs of bo¬ 
dies. —To Ihew that attraftion afts ienfibly only on the 
elementary molecules of bodies, put fulphur in lubftance 
in contaft with alcohol, and there will be no aftion ; but, 
it powdered fulphur be put with the alcohol, then they 
will form an union. To perform this, powdered fulphur 
is to be put into a glals cucurbit, fufpended within a 
vefiel containing alcohol, as fliewn in Plate I. fig. i. of 
the chemical apparatus : put on the head or top, 'and 
fatten a linall matrafs to its neck; then lute all the join¬ 
ings clofe, and heat the apparatus. The fulphur fub- 
limes, the alcohol vclatilifes ; in this ftate the two bodies 
meet; the alcohol diffolvts the fulphur; and a flightiy- 
coloured fluid is found in the matrafs : this is fhlpburate.l 
alcohol. To prove that the fulphur has been dillolyecL 
by the alcohol, add thereto fome diltilled water, and fui- 
phur is precipitated. By putting together ammoniac 
and muriatic acid, the fame elfcft is produced. A white 
linoke immediately arifes ; the muriatic acid mixes with 
the ammoniac, and hence is produced the comnolition, 
called muriat of ammoniac. 
III. Attraction tnay take place between federal bodies , 
as in Darcet’s Mixture.—This is a mixture of eight parts- 
of bifmuth, live of lead, and three of tin. The com¬ 
binations of acids with alkalis may alfo, be brought as 
examples to this rule; the formation of the fulphuric 
acid, or the combination of fulphur with oxygen, &cu 
which Fourcroy denominates complicated attiadfions. 
This term, however, has been rejedted by Morveau, as 
conveying an incorreft notion of what occurs in the 
cafes of chemical combination to which it refers. “ It 
frequently happens, lie obferves, that three feparate bo¬ 
dies, meeting in a fluid ftate, unite and form a Angle 
mals, which has all the charafters of a homogeneous, 
compound, and which retains this charafter, till its com¬ 
pofition has been altered l?y chemical means. Such, for 
example, is the alloy of gold, fiiver, and topper. It has been 
faid, that this triple compound is formed by complicated 
affinity-, but this kind of'expreffion ferves only to divert 
the mind from taking a juft view of the experiment. It 
is not the fimultaneous and reciprocal aftion of the three 
metals on one another, that is eflential to the fuccels of 
the experiment; we have this proof of it, that precifely 
the fame alloy is obtained, whether the gold be firifc 
united to the iilver or to the copper, or though the coo¬ 
per be firft united to the fiiver. We have, therefore, two 
fucceflive combinations during the experiment. In the 
firft of thefe, a particle of one of the metals comes into 
contaft, and unites with a particle of one of the other 
metals ; and, in thefecond, this newly formed compound 
unites to a particle of the third metal, in confequence 
of the aflinit)^ which, as a compound, it acquires for 
that metal. There is nothing peculiar or extraordinary 
in this. We have, as in other cafes, two chemical forces 
afting in fucceffion, and two fucceflive combinations 
formed. What has been faid of the alloy of three me¬ 
tals, may be applied to all fimiiar cafes, whatever be the 
nature or the number of the fubftances employed.” See 
article Affinity of the chemical part of the Encyclopedie 
Metbodique, page 550. 
IV. That bodies may unite chemically, one of the two at 
leaf mttf be liquidorfiuid. —There are bodies which cannot 
analyle themtelves, though they conilantly obey the law 
of fynthefis. There are others which cannot analyle, 
and then unite with other bodies, till after feme prelimi¬ 
nary 
