CHEMISTRY. 175 
•nary preparations have taken place ; thus, it would be 
uleiefs to leave fnlplmr and mercury together in a veffe), 
becaufe they would form no combination ; but, if caloric 
be added, they will readily unite. In the fame manner, 
in making of glafs, if one of the fubftances which en¬ 
ters into the compofition be not rendered, fluid, there 
would be no action between them: we are therefore 
obliged to add caloric ; the alkali is thus rendered fluid, 
the land then melts ; and thus glafs is made. The union 
of an acid with any earth whatever, is another proof of 
the neceiTity of one body being liquid : from this phe¬ 
nomenon arifes what is called a Jolution. Examples 
of the various phenomena of folutipn may be noticed 
from fugarin lump or in powder; fea-falt cryftallifed, or 
in powder, &c. 
V. When the attraction of compofition takes place between 
bodies, their temperature changes. —By applying experiment 
to theory, the truth of this affertion will appear. When 
lime is hilled, we know that there is a. di.'engagement of 
caloric. If concentrated fulphuric acid be mixed with 
watir, a confiderable heat is produced, fo that by plung¬ 
ing in a tube containing water, it will be made to boil: 
the proportion necefihry for this, is four parts of the 
acid to one of the water. If muriat of ammoniac be 
difl'olvecl ip water, a thermometer plunged therein will 
fall confiderably. This effedt will be much more fenfible 
in a mixture of muriat of foda with ice. If a quantity 
of water of .60 degrees of heat be' poured on an equal 
quantity of ice, the melted refult will be o ; 60 degrees of 
heat will therefore have been combined. 
VI. Bodies between which the attraction of cotnpnfilion 
takes place, acquire different qualities from what the bodies 
themfelfoes pojfejfed before. — I his truth is a fundamental 
axiom in chemillry, and infinitely worthy of attention. 
Chemifts in general have thought that the properties of 
a compound body held a medium between the properties 
of the fubftances which compofed it ; this is an error 
which it is important to correCl; a prejudice which it is 
elfential to remove, b'ec'aufe it tends to hinder the pro- 
grefs of the art. This rule therefore requires to be exa¬ 
mined under different points of view. 1. In the tajle, 
exemplified ,by oxygenated muriat of mercury, and ful- 
phat of potafli. Thefe prove, that the taller is very dif¬ 
ferent when the bodies are combined. The firft is moll 
deadly poifon ; yet its conllituent parts (muriatic acid 
and mercury) may be taken feparately without injury to 
the human frame. The fecond is bitter and flightiy pur¬ 
gative, while neither the fulphuric acid nor the potafli 
have of thenrfelves either of thefe properties. 2. In fmell, 
exemplified by muriate of ammoniac, and fulphur of 
'potafli. The muriat of ammoniac affords an example of 
two odorous bodies, which form a compofition without 
fmell. Sulphure of potafli, on the other hand, when 
moillened, gives out a fetid fmell; yet neither fulphur 
nor potafli, in their dry flate, have any fmell. 3. In 
colour, exemplified by red and yellow oxyds of lead : blue 
oxyd of cobalt: green oxyd of copper, &c. By com¬ 
paring thefe different oxyds with the pure metals, it 
will be eafy to fee the difference between them. It is the 
fame thing with relpebt to form, confluence, infufimlity. 
See. Two fubftances which are very infufible, or'very 
difficult to fufie feparately, become very fufible when 
united ; the combinations of fulphur and of metals, af¬ 
ford very ftriking examples of this faft. 
VII. The force of the attraction of compofition is- meafur'ed- 
by the difficulty of feparating the component parts. —Many 
chemifts have taught the contrary of this fact, for the fol¬ 
lowing reafons :—Nitrous acid eafily combines with mer¬ 
cury ; but the muriatic with great difficulty ; he : .ce they 
concluded that the nitrous acid had more affinity with 
mercury than the muriatic acid. This fpecious reafoning 
is erroneous for, if the nitrous acid combines ealiiy with 
mercury, it quits it as eafily ; and, if there is a difficulty 
in uniting the muriatic acid with the mercury, the dif¬ 
ficulty of difengaging it is alfo equally great. Farther, 
if muriatic acid be poured over nitrat of mercury, it 
will unite with the mercury, and f.parate the nitrous 
acid ; which is an evident proof of the truth of this law. 
VIII. There is a <ve>-y different attraction of compofition 
between all bodies in nature .—This we iludl eafily demon- 
ftrate, Fourcroy divides this attraction into Ample or 
Angle elefiiive attractions, and double or compound elec¬ 
tive attractions. If into a diffolution, containing two 
fubftances, we add a third body which produces a fepa- 
ration of one of the difiolved bodies, this body, re-ap¬ 
pearing under a folid-form, takes the name of precipitate, 
and is an example of limple'eleCfive attraction or affinity. 
But there are feveral kinds of precipitates: true, falle, 
pure, and impure. A true precipitate is when the body 
feparated falls to the bottom of the veffel; it is falfe, 
when the mixture is precipitated. A precipitate is pure 
when with the refults the original body may be recom- 
pofed ; it is impure when this cannot be done, and when 
it is poflible to reduce it ftill farther from its original 
ftate. But it is neceffary to obferve that precipitation 
does not always take place in the body expelled or difen- 
gaged ; for it frequently happens, in decompofing a 
body formed of two fubftances by the intervention of a 
third, that the expelled body volatilifes, or is diffipated 
in the form of an aerial fluid. We have an inftance of 
this in the decompofition of muriat of ammoniac by 
means of quick-lime; a calcareous muriat is formed, 
and the ammoniac is volatilifed. 
Double or compound eleCti-ve attraction .—Double affinity, 
is the decompofition of one body by another compolfid 
of two or three fqbftance, but which could not be done 
by thole fubftances taken feparately. This attraction or 
affinity may be considered.in two ftates. 1. Neceffary. 
2. Superfluous; and which may be illuftrated by the fol¬ 
lowing formula : 
Nitrat of foda. 
A 
Soda 
7 . . D . 
O Nitric acid. 
of led-f ^ S- RdMcent "altraClions4=i2 )- ous 
B 
£r. 
o' 
Sulphuric acid 5 Lime 
13 
Calcare- 
ni- 
trat. 
L_ 
Sulphat of lime. 
This table is thus explained : a compofition of fulphu¬ 
ric acid B, and one of foda A, cannot be decoinpofed 
by the lime C, nor by the nitric acid D, taken leparate- 
ly ; but the analyied compound CD will decompole the 
compofition, BA, becaule C and D have lefs affinity to¬ 
wards BA than B and A have to each other, and CD 
have more affinity towards one of thole bodies than that 
body has towards them. The firft are called duvellejit af¬ 
finities, the lall quiefeent. When the quiefeent affinities- 
are ftronger than the diveilenf, it makes no change in. 
the combinations; but, if the divellent affinities are 
ftrongeft, the txilting combinations are broken, and new 
ones are formed. This method of affinities may be fur¬ 
ther explained by the following formula : 
Muriat of potafh. 
Muriat 
of . 
b ary ter. | Barytes 
Muriatic acid. 32 
4- 
36 
P-ctafn 
; 45 
14 Carbonic acid 
'46 
I Carbo- 
/” nat of 
potafh 
Carbonat of barytes. 
If 
