the compounds of chromium. 
2S1 
2. Dichromate of Lead. 
Chromate of lead constitutes one of the richest orange 
coloured pigments in existence ; but it is too well known to 
require any description. The dichromate of lead is easily 
formed by digesting chromate of lead in caustic potash. Half 
the chromic acid combines with the potash, the remainder 
continues united with the oxide of lead. Dichromate of lead 
has a rich scarlet-colour : like chromate of lead it is tasteless, 
and insoluble in water. When heated to redness it becomes 
brick-red, but recovers its original colour on cooling. When 
digested in nitric acid, one-half of the oxide of lead is dis¬ 
solved and chromate of lead restored. The following ex¬ 
periment will show the constituents of this salt. 58-96 grains 
of anhydrous chromate of lead were digested in caustic potash. 
The undissolved scarlet powder being edulcorated and ig¬ 
nited weighed 49’58 grains. 
The potash solution was saturated with acetic acid and 
thrown down by acetate of lead. The chromate of lead ob¬ 
tained weighed after ignition 29-5 grains. But 29*5 is 
almost exactly the half of 58.96 grains, the original quantity 
of chromate of lead employed. It is plain, from this, that 
just one-half of the chromic acid in the salt had been removed. 
All the oxide of lead remaining, and the original salt having 
been neutral, it is clear that the red powder is a compound of 
1 atom chromic acid - 6 5 
2 atoms protoxide of lead 28 
34*5 
