62 
MICRO-CHEMICAL EXAMINATION OF MINERALS. Ma r ; 1889 
hole from one side by means of a fine wire, so as to avoid the 
formation of air bubbles. The preparation must be gently 
heated, a tin box full of hot water, with a lid on which to lay 
the glasses, answers well; and when the first quantity has 
evaporated, a second, and, if necessary, a third and fourth 
drop may be added. Finally the acid is replaced by water, 
and the soluble salts removed by a very fine pipette made of a 
piece of narrow glass tube drawn out to a very fine point. 
This solution is then distributed into separate drops on a glass 
slide, and the further examination proceeded with. 
If a minute grain can be separated, the decomposition of 
it may be effected in a little platinum spoon, such as is used 
in blowpipe analysis. The action of the acid is much 
facilitated by the fine grinding of the specimen to be 
examined. This should be effected either on a polished steel 
anvil with a polished steel pestle, using a ring of glass to 
prevent the dispersion of the powder, or in an agate mortar. 
If porcelain were used the abrasion of the mortar might 
occasionally introduce sufficient impurity to falsify the results 
of the subsequent tests. 
The hydrofluoric acid may be replaced by fluoride of 
ammonium, which can now be procured in a state of very 
great purity. In this case, however, the residue of salts must 
be heated to redness, in order to be sure of getting rid of all 
trace of ammonia, as this, by the similarity of its reactions, 
might easily be taken for potash. The action also is said 
to be less energetic than that of hydrofluoric acid, so that 
probably the acid is the better of the two, although being 
solid the salt is by far the more convenient. In any case 
when the fluoride compounds are dried up, or nearly so, a 
drop of sulphuric acid, diluted somewhat with water, must 
be added, and the whole again gently heated. If the 
sulphuric acid has been added in sufficient quantity the 
excess will be driven off in a dense cloud, and if this does not 
take place another drop must be added, and the evaporation 
repeated. It is advisable not quite to dry up the mass of salts, 
as when quite dry they dissolve in the water which is next 
added with much greater difficulty. 
If the operations have been successfully performed, we 
shall have a solution of all the bases of the mineral in 
combination with sulphuric acid, and, as before stated, this 
must be distributed in drops on to glass slips by means of a 
finely drawn out glass tube. 
If one of these drops is allowed slowly to evaporate, and 
is observed from time to time with a power of about 100, the 
presence of Lime will be shown by the formation in the drop, 
