M. Marchand on the Reduction of Chromate of Lead. 533 
Many persons imagine that in organic analysis with chromate of 
lead it is necessary to use a very strong heat in order to perfect the 
operation. This is a mistake, for carbon as well as hydrogen very 
easily reduces the chromate. If however it is required to libe- 
rate oxygen, then the temperature must be very great, and the 
salt must be fused. This circumstance, as may be easily conceived, 
is inconvenient and liable to introduce error. 
When chromate of lead is heated in a current of hydrogen gas, it 
commences to glow at a heat far below redness, and a quantity of 
water is formed. The yellow colour of the salt disappears ; it be- 
comes black, and very small metallic globules are disseminated 
through the mass. 
3-049 grammes lost 0*307 gram, or 10'07 per cent, of oxygen ; 
this loss may be increased by a continued and strong heat. 
1*91 grammes lost in another experiment 0*224 gram., or ITS 
per cent, oxygen. At the commencement of the reduction of this 
portion the temperature was kept moderate, by which it lost 0-2045 
grm., or 10*7 per cent. Oxygen gas was then passed over it 
while in a heated state. At a low degree of heat, the mass burnt 
with great brilliancy, turned brown, at least partly so, which was 
very evident on cooling. It absorbed 0*133 grm. oxygen, which 
calculated for the original quantity (1‘91) amounted to 7 per cent.; 
a small quantity of water was formed during the operation, amount- 
ing, however, to but a few milligrammes. It would therefore 
appear that hydrogen was condensed in the pores of the reduced 
mass, but in a small quantity ; heating in a stream of carbonic acid 
gas would have entirely driven it out. The oxidated quantity 1*839 
grm. which had lost from the first 3*7 per cent, of oxygen, was 
again reduced in hydrogen gas, by which it lost 0*152 grm., this 
upon the whole quantity is equal to 8 per cent. Upon heating in 
oxygen gas the same appearances again took place, and the mass 
absorbed 0*128 grm., therefore, a similar quantity as before. A 
subsequent reduction at a very high temperature occasioned a loss 
of 0*128 grm. while a repeated oxidation only gave an increase 
of 0*119. This was again driven out by hydrogen, but without any 
further decrease of oxygen. 
If we examine these experiments, keeping in view the results, 
we shall find that 1*91 grm. lost 0*224 grm. equal to 11*8 per 
cent, while the last oxidation was only 1*19 grm. or 6*2 per cent. 
Chromate of lead contains 19*54 per cent, of oxygen, equal to four 
atoms, Cr Pb. 11*8 j5er cent, is equal to 2*4 atoms or nearly ^ths of 
the whole amount of oxygen. This would be 12*2 percent. The 
reduction, if complete, would convert all the oxide of lead into the 
metallic state and the chromic acid into the state of oxide of chrome. 
2 Cr + 6 O 2Pb -f 2 O 
3 0 2 0 
2 Cr + 3 O 2 Pb. 
By oxidation about half of the oxygen is recombined ; this takes 
place the more readily when the metallic lead is in a finely divided 
