162 NON-METALLIC ELEMENTS IN BINARY COMPOUNDSwhich the primary positive valence of the metallic constituent is
just equaled by the primary negative valence of the non-metallic
constituent. The peroxides could rather be classed with such
compounds as nitrates and sulphates in which there is a compound
negative radical.
- Dioxides. To about 1 gram each of manganese diox-
ide, MnO 2 , and lead dioxide, PbO 2 , in separate test tubes add
10 cc. of water and 5 cc. of 6iV H 2 SO 4 or HN0 3 and warm
for a few moments. Note that the dark-colored powders
do not dissolve or change their appearance in any way,
nor is there any effervescence. Filter off the insoluble pow-
der and add titanium sulphate to the filtrate. Note that
there is no yellow coloration.
These two oxides do not react at all with these acids, and indeed
we should not expect on that account to find any hydrogen perox-
ide produced. These results are merely negative, therefore, and
leave us in doubt as to the nature of the oxides, whether they are
ordinary binary oxides in which case the valence of the manganese
or lead is 4, or whether they are peroxides in which the valence
of the metal is 2 like that of barium in barium peroxide. - Different Behavior of Dioxides and Peroxides with Hy-
drochloric Acid, (a) Treat 0.5 gram of finely powdered lead
dioxide with 5 cc. of ice-cold 12 N HC1. Note that a yellow
solution is formed. Dilute 1 cc. of the solution with 100 cc. of
water and add 1 cc. of titanium sulphate. Note that no yellow
color is produced. Heat the rest of the solution. Note that
yellow gas (chlorine) is given off, that the yellow color of the
solution disappears, and that a white crystalline solid settles
out as the solution cools. (6) Treat 0.5 gram of barium perox-
ide in the same way with 5 cc. of ice-cold 12 N HC1. Add cold
water until all the crystalline residue is dissolved; dilute 5 cc.
of this solution with 100 cc. of water and add 1 cc. of titanium
sulphate. The yellow color indicating the presence of hydro-
gen peroxide is obtained. Warm the remainder of the solu-
tion. Note that little or no chlorine is evolved. Dilute
5 cc. of the remaining solution with 100 cc. of water and again
add titanium sulphate. Note that the test for hydrogen
peroxide is still obtained unless the solution had been heated
too long.