MTCROCHEMICAL REACTIONS OF THE COMMON ACIDS 
415 
9. Always test the precipitate obtained by NH4OH for Al, Mg, Fe, Mn, Cr, Sn, (Si), 
(Bi), (Sb), (Hg). 
Take a portion, treat v/ith HNO3 and evaporate to dryness. Repeat several times to 
convert any Sn into the oxide. Dissolve any insoluble material in HNO3 + HCl and test 
for Sn and Sb with CsCl. 
Test another portion with HNO3 and a fragment of KCIO3 and heat to boiling. Mn will 
be precipitated as Mn02, Cr will be oxidized to a chromate. Decant or filter. Test residue 
for Mn and solution for Cr04. 
10. To a drop of H2O or HNO3 solution add HCl:—^ Ag, Pb, Hg. Treat any amor¬ 
phous precipitate with NH4OH: — Ag, Hg. 
11. To a drop of solution add dilute H2SO4. A crystalline precipitate indicates Ca, Ag, 
Hg; under certain conditions Sb, Bi may yield crystalline precipitates as may also a num¬ 
ber of difficultly soluble stable salts. An amorphous precipitate indicates Sr, Ba, Pb. 
(Rarely all three of these elements yield crystalline precipitates.) 
12. Evaporate to dryness a drop of the solution of the substance after acidifying with 
HNO3. Dissolve the residue in a drop of water and add a fragment of potassium mercuric 
thiocyanate reagent. 
A cr>stalline precipitate Zn, Cu, Cd, Co, Ag, Pb, Au, (Ni), (Mn). 
Amorphous precipitate, Pb, Ag. 
Red or pink color, Fe. 
(If the oxidation of Fe or Mn salts has not been complete, an amorphous or crystalline 
precipitate may be obtained, see page 356. Around the edges of the drops, crystals of the 
components of the reagent always eventually separate.) 
13. To a moderately concentrated solution add a fragment of KI: — Pb, Hg, Ag, (Cu). 
14. To a very concentrated drop of the substance to be tested (which must not contain 
free HNO3) add a drop of dilute HCl. Introduce zinc sulphide fibers, warm and examine. 
Evaporate to dryness, add NH4OH. Examine the fibers again and introduce one or two 
new fibers. 
In acid solution the fiber is: 
Lemon j'ellow — As, Cd. 
Reddish yellow — Sb, Bi. 
Straw yellow — Sn. 
Brownish yellow — Ag, Bi, Cu, Hg, Pb, Sb (Co, Fe, Mn, Ni). 
Black — Ag, Bi, Cu, Hg, Pb. 
In acid solution no color, but in alkaline solution the fiber may turn: 
Brownish — Co, Fe, Mn, Ni. (These elements rarely give good reactions with the 
fibers.) 
15. To a moderately concentrated drop containing a trace of HNO3 add CsCl and KI 
(see page 400); crystalline precipitates are obtainable with Sn, Sb, Bi, Pb, Hg. Amor¬ 
phous precipitates with Ag, Hg. Iodine often separates, especially in the presence of Cu. 
16. In the above outline no satisfactory indication for the presence of the following have 
been obtained: Na, NH4, Ni, Si, Bo, As. Hence apply suitable identity tests for these 
elements. 
17. Remember that carbonates and hydroxides must be converted into chlorides or 
nitrates (or sulphates) before being tested for bases. 
18. The material is insoluble in water and in acids: Crush to the finest possible powder 
in a tiny agate mortar. Fuse with Na2C03, with K2CO3, or with HKSO4, using the smallest 
possible amount of reagent. Test in the usual way for Si with NH4F and NaCl and for 
the bases after treatment with acid and removal of tlK Si02. 
In some cases silicates may be decomposed by heating in a tiny platinum cup with NH4F 
and H2SO4. 
19. Rernember to te.st for NH4 and for Mg. In the presence of ammonium salts Mg is 
not precipitated by NH4OH, or if a precipitate is formed it slowly disappears. 
THE COMMON ACIDS. 
In the elementary course whose outline is covered by this 
textbook the identification of the acid radicals in simple sails 
or simple mixtures alone is undertaken. With materials of this 
nature the qualitative analysis is comparatively easy and no 
elaborate directions or schemes of procedure are necessary. 
Most of the tests for the acids have already been studied and 
