66 
MANUFACTURE OF OXALIC ACID. 
A large quantity of mother-liquor remained, from which 
no crystals were attempted to be obtained, as these may be 
set against the small produce of experiment No. 1. If then 
we omit this experiment altogether, we shall have an aver- 
age of the seven following, showing that 196 of sugar and 
128S of diluted nitric acid, have produced 214f of oxalic 
acid and 150| of carbonic acid, and that the proportion of 
carbon in the oxalic acid obtained almost exactly equals 
that in the carbonic acid, and that by the action of nitric 
acid in the way described, one-half of the carbon of any 
given quantity of sugar, is converted into oxalic acid, and 
the other half into carbonic acid. I have made many ex- 
periments with nitric acid of various densities and at various 
temperatures, but without obtaining in any instance so 
large a produce of oxalic acid, as with acid of the strength 
indicated. When strong acid is employed, the temperature 
rises too high, and a quantity of formic acid is occasionally 
produced, which distils over into the receiver, and materially 
diminishes the produce of oxalic acid. From these experi- 
ments it would appear that no more than 124lbs. of oxalic 
acid can be obtained from a cwt. of sugar. This, I am 
aware, is much below the quantity generally supposed to 
be produced on the large scale, and which is stated to vary 
from 135 to 140 lbs. for the cwt. of sugar; such acid is how- 
ever contaminated with nitric acid and mother liquor, and 
is moreover decidedly damp, as shown by the manner in 
which the crystals cling to the sides of the bottle in which 
they are contained — some allowance must also be made for 
the tendency to exaggeration which prevails in our manu- 
factories. Of this at least I am sure, that in some hundreds 
of attempts conducted on a pretty large scale, I have never 
once exceeded the amount here stated (124 lbs.) when the 
acid was properly purified and freed from adhering moisture. 
The following diagram in my opinion represents the nature 
of the ultimate decomposition which ensues in this manu- 
facture, although other substances are unquestionably pro- 
duced in the first instance : — 
