22 QUANTITATIVE AGRICULTURAL ,1 AM/,}'*/*
Sampling of Liquids.—In case the substance to be* analyzed
is a liquid the operation of sampling is usually a simple one,
,| consisting of thorough mixing before the removal of the proper
quantity for analysis.
Dissolving the Sample.—After the sample* of substance
has been properly selected and weighed the next operation i.s
usually one of solution. What the solvent shall be is determined
by the nature of the sample and by the character of the oj>era-
tions subsequently to be performed. Water may be used,
or concentrated or dilute solutions of acids, base* or .salts,
organic solvents or solid substances used as (luxes by heating
to high temperatures. In case gravimetric methods an* to bet
employed it is desirable to use a relatively small quantity of the
solvent, not only because it must finally be entirely removed,
but also because all precipitates dissolve to some extent and it is
only by keeping the amount of solvent down to the least cjuant.it y
that is workable that the loss of precipitate* is reduced to the
minimum.
Fusion.—For the purpose of quantitative analysis t he fusion
of materials is almost always accomplished with the end in view of
producing more soluble substances through the internet ion of
an added agent, called a flux, and the refractory material.
For instance, most of the natural silicates are practically insoluble
in water and all ordinary reagents and therefore they cannot
be analyzed by ordinary methods. By a preliminary heating
to a high temperature in contact with a basic substance like
sodium carbonate, a fusible mixture of new cxmipounds in formed
and these will, for the most part, be soluble* in water and hydro-
chloric acid so that the solution may be submitted to precipita-
tion and filtration processes for the separation and dctterminuf ion
of the elements. Similarly, refractory and insoluble metallic
oxides may be heated with sodium pyroBulphate with the forma-
tion of a fused mass consisting of soluble milphates of the inctjtR
The necessary qualities of any useful flux arc (1) that it muni
be of such a nature as to be capable of reacting with the refract ory
body when heated with it and (2) that the refilling eotiipouitdH
shall fuse at the prevailing temperature. To the.se. the* analyst
[1 adds a th"*d requisite: (3) that the resulting compounds Khali
[ \ be soluble in water or in the laboratory reagents. The* first