f/A'A" KKA L OPERA Tin A*,S'

porcelain is usually unsuitable because the funed material will
combine with the glaze, or even with the porcelain itself. For
such work platinum or oik* of the newer Hubst.Itutes, palau or
rhotanium, is (essential.
Marking Crucibles. Metal crucibles should have permanent
identification numbers stamped upon them by means of small
dies. These numbers form a part of the analytieal record and
they serve to prevent accidental transposition of weight records.
Porcelain crucibles may best be marked by means of n pen
and ink, the. marks being inconspicuous figure* or small dots,
When the crucible is strongly heated the iron of the ink forms
the red oxide, which burns into theglavse and forms a permanent
identification mark. ((Vrtain common inks do not- contain iron,
iso that they are unsuitable for this purpose.)
Some manufacturers of chemical porcelain now furnish cruci-
bles and dishes serially numbered with permanent marks. This
is a great convenience to tint analyst..
Care of Platinum.- Platinum wan* will deteriorate rapidly
unless the following precautions arc taken in its use and cure.
 1.	Handle*  carefully  to  avoid   bending,    I'se  clean  crucible
tongs and do not allow the tongs to come into contact, with fused
materials within the crucibles or dishes.
 2.	For cleaning apply the appropriate1 solvent, according to
the nature* of the material to  be removed,    C 'hromic ncid   is
suitable for removing organic nta.tt.cr, and hydrochloric or nitric
acids for insoluble  carbonates or metallic oxides;  fusing with
Bodiurn carbonate is suitable for removing silica or silicates, or
with sodium pyroBiilphate for .such metals or metallic oxide?* »,m
resist the* action of acids.
 3.	Do not heat platinum in contact, with the inner cone of the
laboratory burner, an britiU*nc*HH results from mtch t*x(Mwun*.
 4.	Do not  heat compounds of lead,  tin,  biwinuth,  HrHrmc,
antimony or mtc in run tart with platinum.    Reduction may
occur, the reduced metal alloying with the platinum,
f>. Do not attempt to remove Fusions from platinum eruribli'M
or dishes by means of files, glass rods or other bard too!*, l^r
solvents or a rubber-tipped rod.
0. Dull surfaces should her polished tightly with wet emery
slime or fine carborundum.

fcl