jy6 
CHEMISTR Y, 
If a folution of inurlat of barytes be mixed with a 
folution of carbonat of potalh, the affinity of the mu¬ 
riatic acid with the barytes, and that of the potaffi with 
the carbonic acid, are quiefcent affinities. The affinity 
of the muriatic acid with the potafh, and that of the 
barytes with the carbonic acid, are divellent. Thefe 
lalt are ftrongell or molt numerous : the firft combinations 
are broken; and, inftead of muriat of barytes and car¬ 
bonat of potalh, we have muriat of potaffi and carbo¬ 
nat of barytes, which, being inlbluble in water, is pre¬ 
cipitated. 
In every cafe where more than three bodies are requir¬ 
ed for the production of any chemical change, we are to 
confider the change as depending not on fimple affinities, 
or on the independent affinities of fmgle bodies to one 
another, but upon the fum of all the affinities that con¬ 
cur in tending to the lame end. To illuilrate the prin¬ 
ciple, that in double elective attractions, the condition 
by which decompofition is determined, is the relative 
fum of the divellent and quiefcent affinities, and not the 
itrength of any fingle affinity in particular, it may be 
proper to give an inftance in which no decompofition takes 
place, when two fubftances are ufed together, though 
either of them could have effected it if employed fepa- 
rateiy. The acetit of lime is decompofed by loda; it is 
alfo decompofed by the muriatic acid ; yet it refills the 
aftion of the muriat of foda. The following table will 
illuftrate this : 
Acetit f Acetous acid 25 Soda 1 Muriat 
of < 19 -j- 28 I —47 > of 
lime. I^Lime 20 Muriatic acid J 
= 45 I 
In this inftance the affinity of foda with the acetous acid 
is greater than the affinity of lime with the acetous acid; 
and the affinity of the muriatic acid with lime is greater 
than the affinity of the acetous acid with lime; but the 
fum of the quiefcent affinities is greater than the fum of 
the divellent affinities, and therefore no decompofition 
takes place. In many cafes of chemical mixture, the 
affinities of more than four fubftances are concerned ; 
and, though fuch cafes are of the fame nature with thole 
of double elebtive attraction, yet that term feems inap¬ 
plicable to them, as it implies the agency of only four 
fubftances. Morveau has, therefore, lubftituted the lan¬ 
guage of concurrent affinity (affinite par concours), as the 
general expreffion for that tendency to chemical combi¬ 
nation, which is rendered efficacious by the conjoined 
operation of more affinities than one. It is probable that 
this expreffion will be adopted in the place of Bergman’s, 
which is evidently too reftrifted in its literal application. 
It may alfo farther be obl'erved, that in every chemical 
combination which is preceded by decompofition, the 
divellent and quiefcent affinities mull be equally attend¬ 
ed to, in order to form a proper efcimate of the experi¬ 
ment ; for the quiefcent affinities, even when they cannot 
prevent decompofition entirely, are Hill able to diminilh 
the promptitude with which it takes place, and frequent¬ 
ly to Hop its progrefs at a lower point of faturation than 
the divellent l'ubltance would otherwife require. It will 
alfo happen, on fome occafions, that the concurrence of 
feveral divellent affinities, though not abfolutely necei- 
fary to produce a particular effedl, will yet accomplilh 
it more completely, and with greater facility, than any 
of them ftngly could have done. 
IX. Attraction in the inverfe Ratio of Saturation .—If 
fulphuric acid be brought in contadl with mercury, we 
Ihall obtain, by the help of caloric, fulphureous acid nnd 
fulphat of mercury. A part of the acid then is decom- 
poied; the oxygen which made it fulphuric acid has 
oxydated the mercury. The firft portions of the oxy¬ 
gen then are eaiily difengaged, while the laft adhere 
itrongly to the fulpliur; lienee it arifes that the firft 
molecules which unite to a body adhere much more ftrong- 
ly than the laft; and, in proportion as it approaches to 
the point of faturation, the molecules adhere lefs and lefs 
to the body, fo that it is often very eafy to feparate the 
firft molecules from the principles of a compound, while 
the latter molecules are feparuted with great difficulty : 
and of which the example above given is a linking proof. 
Predifpofng Attractions .—Sulphur works no change.up- 
on water; which proves that fulphur has lefs attrablion 
for oxygen than hydrogen has; but, if fulphur be united 
v.’ith an alkali, this compofiticn decompofes water, thougli 
the 3 lkali itfelf has no attraction for the oxygen ; the 
alkali then can onlylae attracted by the fulphuric acid, 
which Ihould be formed by the union of the fulphur with 
the oxygen of the water. This attraction favours the 
decompofition of the water, and is what is called predif- 
pofmg' attraction. The refults of the experiment are, an 
alkaline which has the property of decompofing water 
when brought into contafil; a fulphurated hydrogenous 
gas is expelled, and the oxygen of the water flies upon 
the.fulphur which is formed of the fulphuric acid, and 
which poffeffes itfelf of the alkali to form a fulphat. 
To thefe laws of chemical affinity propofed by Four- 
croy, M. Morveau has added the following two: I. He 
Ihows, by a variety of initances, that when two bodies 
are prefented to one another, the faturated compound 
which refults from their union is capable of combining 
with an accefs of one of its conftituents; but the affinity 
which produces this laft combination is not the fame with 
the affinity which unites together the conftituents of the 
compound itfelf; nor has it any known ratio to this lat¬ 
ter affinity, but appears in every cafe to be very much 
inferior to it in ftrength. The following is an appofite 
illuftration of thefe faffs and inferences. The fulphat of 
barytes is one of the ftrongeft combinations in chemiltry 
and one of the moll perfefl neutral falts. When the 
concentrated fulphuric acid is boiled over this fait, a 
confiderable quantity of it is diffolved by the acid, and 
this quantity is inftantly precipitated by the addition of 
water. We have in this cafe a faturated compound (the 
fulphat of barytes) uniting with an excels of the fnl- 
phuric acid, but forming with it a combination infinite¬ 
ly weaker than the fulphat of barytes, lince it is decom¬ 
pofed by the fingle affinity of the fulphuric acid with 
water. The following cafe will lerve as another example 
of a compound uniting with an excefs of one of its con- 
llituents, and at the fame time will explain an apparent 
exception to the ordinary laws of chemiltry. It is 
known that the fulphuric acid has a greater affinity w'ith 
potalh than the nitric acid has. Yet Baume, having 
diffolved the fulphat of potalh in an equal w’eight of the 
nitric acid, obtained, after filtrating and evaporating the 
liquid, a confiderable quantity of cryltallized nitrat of 
potalh. In this curious experiment there is a part only 
of the fulphat of potalh decompofed, and what remains 
is combined with an excefs of acid. From thefe data, 
and from analogous experiments with the muriatic and 
tartarous acids, Morveau has conftrufted the following 
table, to explain in what manner part of the fait is de» 
compofed. 
Nitrat of potalh#. 
_ 
r 
Nitric acid. 
58 
1 
Potalh faturating 
z 
+ 
about one third of 
the neutral fait. 
62 — 64 
Sulphatof potalh which 
34 
Sulphuric acid faturat- 
remains undecompofed. 
— 
ing the fame quantity 
_ 
— 9 Z 
of the fait. 
j 
; v— 
Sulphat of potalh with 
an excefs of acid. 
To take but one other example :—Morveau procured 
oxalate of lime, by adding lime-water to the oxalic acid; 
the liquor was lliil mamfeltly acid; he feparated the oxa¬ 
late. 
