6 
employed. The latter consists principally in the applica¬ 
tion of the blowpipe, the former in the solution of bodies 
in water, acids, etc., and the application of certain re-agents 
by which precipitates of particular colours and conditions 
are thrown down. In both cases the object is either to 
obtain decomposition or new combinations, which may 
once more be analysed. 
In using the blowpipe, small fragments of the mineral 
may be held either on charcoal or in platinum forceps, so 
that first the fusibility, and then the escaping vapour, or 
the deposit left on the charcoal, as well as the residue, is 
examined, either by reducing it in the inner flame, or 
by forming from it, along with borax, soda, and salt of 
phosphorus, a pearl-like drop, which is also to be con¬ 
sidered with reference to its colour and appearance. It is 
to be kept in mind, in using the blowpipe, that the point 
of the flame has an oxidising power, and the inner blue 
cone has a reducing influence, that is, it has the power of 
deoxidising ; also, that metals easily fused or reduced 
should not be held in the platinum forceps. Many bodies, 
such as chalk, become exceedingly brilliant when heated, 
others colour the flame at once, or after being held in it 
for some time. Thus, for example, all calcareous minerals 
colour it vermillion-red, strontium gives a brilliant purple- 
red, lithium a pale purplish-red, potassium a violet, 
sodium a pure intense yellow, baryta a green, boracic 
acid a pale green, acetate of copper a green, chloride of 
copper a blue, and the presence of chlorine may be easily 
distinguished in this way by the addition of some oxide of 
copper; while, on the other hand, the presence of copper, be 
it of ever so small amount, may be easity recognised by 
the bright blue flame on moistening the test with a drop of 
hydrochloric acid. The colour which certain metallic 
oxides impart to a bead or pearl of borax, which has been 
obtained by burning on charcoal, when heated on a 
platinum wire, is likewise important. Thus, the oxide of 
cobalt colours it blue, the oxide of copper imparts a green 
colour, and, if a granule of tin is added, it becomes red, 
peroxide of iron makes it yellow when hot and an olive- 
green when cold, protoxide of iron gives a grass green, 
oxide of chromium an emerald green, oxide of manganese 
an amethyst red, oxides of manganese and iron together 
give a blood red or garnet colour, and so on ; while the 
oxides of zinc, lead, and bismuth, do not change the colour 
of the bead. Further details will be found in the descrip¬ 
tions of the individual minerals. The analysis by water 
is best performed in a closed glass tube, or in a small 
retort over a spirit lamp, by which means small drops are 
deposited on the colder part of the tube. This experiment 
serves at the same time to distinguish the water from the 
carbonic acid, both of them producing small beads in the 
borax pearl. 
The presence of carbonic acid is best recognised in the 
moist way, by solution in hydrochloric and nitric acids 
until effervescence takes place. 
Sulphur and sulphuric acid may be detected by using 
finely-powdered specimens along with soda in the inner 
flame, by the aid of which a sulphuret of soda is produced, 
and this, when moistened by a drop of water, and brought 
info contact with a silver coin, leaves a brown stain, and 
gives off an odour of rotten eggs (sulphuretted hydrogen). 
The presence of siliceous earths is best ascertained by 
melting the powdered mineral along with borax or soda, 
while to the clear pearl which is formed there is to be added 
salt of phosphorus ; and thus, after continued heating, the 
siliceous earths may be recognised in the shape of beads 
or points. The analysis by the moist way may be per¬ 
formed either with acids or water. 
Water can only dissolve a few natural salts, as, for 
example, rock salt, alum, carbonate of soda, sulphate of 
soda, potass, salts of magnesia, protoxide of iron, oxides of 
copper and tin, and lime ; the solution of each of these has 
a peculiar taste, and when evaporated in a watch-glass, 
leaves behind the dissolved salt, which may now be readily 
analysed by the ordinary chemical process. 
The acids act on several compounds of silica, espe¬ 
cially such as contain water (the hydrous silicates), as, for 
instance, the zeolite; they have also a solvent action on 
calcareous felspar, so that the silica separates like a jelly 
or slime; other silicates must first be melted, or mixed 
with alkalis, if they are to be further examined. On the 
other hand, the acids dissolve most metallic oxides with a 
determined colouring, which is indicated to some extent in 
the accounts of the individual minerals. 
RELATIONS OF THE CHEMICAL CONSTI¬ 
TUENTS TO CRYSTALLINE FORMS. 
Each mineral, the chemical composition of which has 
been determined, appears, when viewed externally, to be 
physically and crystallographically endowed with the same 
properties, so that not only the hardness, weight, colour, 
and lustre, but also the form of the crystal, show a certain 
constancy. There are instances, however, in which the 
same chemical compounds, or even simple bodies, crys¬ 
tallise in two or three different primary forms, and under 
these circumstances, the hardness and weight also present 
modifications. Such bodies are called dimorphous or di¬ 
morphous • the oxide of titanium, Ti, which occurs as 
rutile, anatase, and brookite, offers a fine example^f 
this, as well as sulphuret of iron, sulphur, and even a few 
metals. On the other hand, different, but chemically related 
elements often present very harmonious relations of form, 
so that, in their composition, the one may be totally or par¬ 
tially substituted for the other, and the crystalline form 
remain unchanged ; this is called isomorphism. Thus, for 
example, magnetic iron ore, composed of like equivalents 
of the protoxide and peroxide of iron, is isomorphous with 
octahedral titanic iron, chromic iron, franklinite, galenite, 
or zinc spinel, and generally with the spinel. In all there 
is a one-atom base, RO or R, with one equivalent of a 
one-and-a-half-atom negative constituent, R 2 0 3 , or R, and 
all crystallize as regular octahedrons. The protoxide of 
iron is sometimes replaced by oxide of tin, sometimes by 
magnesia, the peroxide by oxide of titanium, oxide of 
chromium, or alumina. There are many similar examples 
of this; many bodies, moreover, occur both in the amor¬ 
phous , or glassy, and compact form, in the gaseous or 
vapour-like condition of aggregation, or in a state which 
admits' of their transformation thereinto. 
