interest whether these are in chemical combina- 
tion or merely mixed together. If, therefore, in- 
spection does not lead to distinguish the ingre- 
dients, their separation is effected as if it were a 
chemical combination, without reference to its 
mixed nature. 
It has already been stated that all substances 
are either elementary bodies or their chemical 
combinations, or mechanical mixtures of both. 
Those substances which chemistry is not capa- 
ble of separating into others, it calls elementary 
bodies, and then proves all the rest to be formed 
by their union or combination. Two elements 
form, by their union, binary combinations, but 
when these again combine, the result is a more 
| compound body, containing three or more ele- 
ments. On the other hand, most of the more 
| compound bodies may again be separated into 
| binary, or at least less compound bodies. 
| latter are then said to be the proximate consti- 
These 
tuents of the more compound body; while the 
elementary bodies into which it is finally resolved 
are called its wltimate constituents or elements. 
Thus, oxygen combines with sulphur, forming 
sulphuric acid, and with potassium, forming oxide 
of potassium or potash; but sulphuric acid com- 
| bines again with potash, and forms sulphate of 
| potash. Oxygen, sulphur, and potassium, are 
then said to be the ultimate constituents or ele- 
| ments of sulphate of potash, while sulphuric acid 
—— = 
and potash are its proximate constituents. When 
the proximate constituents of a substance are 
known, we may generally infer from them the 
ultimate constituents; and, vice versa, if the ulti- 
mate elements are known, theoretical chemistry 
will generally teach us which are the proximate 
constituents. Analysis may, therefore, in more 
| compound bodies, discover and determine either 
the proximate constituents, or the elements. This 
is altogether accidental, and depends on the pe- 
culiar method adopted, or on the facility with 
which either the proximate constituents or the 
elements are detected and estimated. Thus, for 
instance, if the above substance, sulphate of pot- 
ash, were unknown to us, and therefore sub- 
jected to analysis, whether we should first dis- 
cover the sulphur or the sulphuric acid, would 
probably depend on the method adopted. If we 
first examine it by the blowpipe, the sulphur 
would probably be first made apparent; while, 
if we first tested it in the moist way, we should 
recognise the sulphuric acid. In the same man- 
ner, in determining the relative quantity of the 
constituents, we should neither estimate directly 
the quantity of sulphur by itself, nor that of the 
sulphuric acid, but transfer them both to a com- 
bination, from the quantity of which, either that 
of the sulphur or of the sulphuric acid may be 
calculated with equal facility. It is therefore 
indifferent of itself, whether we give the result 
of the analysis in so many parts of sulphur, oxy- 
gen, and potassium, or so many parts of sulphu- 
ric acid and potash. Convenience and custom, 
- ANALYSIS. 
165 
or theoretical notions, decide here, as in other 
matters. 
In regard to the analysis of chemical combina- 
tions, it may be remarked that, as it is a neces- 
sary consequence of chemical combination that 
the constituents, either ultimate or proximate, 
which enter into combination, necessarily alter 
more or less their original nature and properties, 
none of the constituents of an unknown chemical 
combination can be recognised with certainty in 
it from its nature and properties. It will there- 
fore be seen, that in order to find what consti- 
tuents it is composed of, it becomes necessary to 
overcome the afiinities by which the latter are 
held in combination, so as either to set them free 
and make them appear with their original pro- 
perties, by which they may be recognised, or to 
transfer them to other combinations, which are 
either known or may be recognised. It would 
thus be impossible to recognise hydrogen or chlo- 
rine in chlorohydric acid gas; nothing could be 
more totally different from either of its consti- 
tuents. But, if we introduce a piece of metallic 
zinc into the gas, the affinity of the zinc to the 
chlorine will overcome the affinity of chlorine to 
hydrogen. The chlorine will therefore be taken 
up by the zinc, and leave the hydrogen in its 
free state, which can then be recognised by its 
usual properties. 
Another mean which analytical chemistry em- 
ploys for overcoming existing affinities and set- 
ting the ingredients free, or transferring them 
to other combinations, is héat, which often will 
induce the gaseous elements to separate and as- 
sume their free state. Oxide of mercury may 
thus be separated into its two elements, oxygen 
gas and metallic mercury. Carbonate of lime is 
separated by ignition into carbonic acid gas and 
lime. Volatile liquids and solids may also be 
expelled by heat from their combinations, by their 
tendency to assume the gaseous state at higher 
temperatures. Thus, chemically combined water 
is generally discovered by heating the substance 
in the closed end of a glass tube, when it will be 
expelled, and condense in the colder part of the 
tube. 
Electricity is another agency for overcoming 
affinity. It was by this agency that Sir Humphrey 
Davy discovered the metallic radicals, and the 
compound nature of the alkalies. 
But the mean most often made use of in ana- 
lyses of substances is chemical affinity itself, either 
single or double elective affinity. In the former 
case we have a combination of two constituents, 
and present to it a third substance, for which 
one of the constituents has a greater affinity than 
for the other, and therefore leaves the latter in 
its free state, and combines with the substance 
added. Thus, if uric acid be in a solution, com- 
bined with a base, and a stronger acid be added, 
to which the base has a greater affinity, it will 
combine with the latter, and leave the uric acid, 
which thereby is separated in its free state, as 
