ON THE MANUFACTURE OF OXALIC ACID. 
243 
charged with nitric acid and the saccharine material used, are 
placed in water-baths capable of holding a hundred or more of 
these jars. These baths are constructed of brick and lined with 
lead, and are heated by means of steam passed through coils of 
lead pipe placed therein. 
Instead of earthenware jars, vessels of lead, or of wood lined 
with lead, may be employed in the manufacture of oxalic acid. 
For this purpose, square open vessels, 8 feet square and 3 feet 
deep, are a convenient size, the liquor being heated by means of 
steam passed through a coil of lead pipe. A coil of about 48 feet 
of one-inch pipe, in a vessel of the size above mentioned, is suffi- 
cient to keep the liquor at the required temperature. In using 
these vessels, the liquor (whatever it may be) to be converted into 
oxalic acid is put into them, together with the acid employed, and 
heated until the required decomposition is effected. The liquor is 
1hen drawn off by a syphon, or by a cock placed at the bottom of 
the vessel, into shallow leaden vessels, or wooden vessels lined 
with lead, to cool and crystallize, and the mother-waters are 
drawn off from the crystals and used in the next operation. 
When the manufacture of this acid is conducted in large ves- 
sels as above mentioned, the specific gravity of the nitric acid em- 
ployed may be less than when the earthenware jars are used. 
From 1.200 to 1.270 are about the limits of the range allowed for 
the gravity of the acid. As regards the temperature of the baths, 
this should be maintained at or about 125° F. Whilst the opera- 
tion is in progress, the active evolution of gas, without the appear- 
ance of red fumes, and the emission of a peculiar smell, slightly 
indicative of the presence of nitric oxide, are amongst the signs 
that everything is in good working condition. The judicious ad- 
dition of sulphuric acid is found to contribute to an increase of the 
quantity of oxalic acid produced. The product of acid from a given 
quantity of sugar has been much understated by chemical writers; 
this has most probably arisen from the circumstance of boiling 
the sugar with strong nitric acid, by which means a large quantity 
of oxalic acid becomes converted, as soon as formed into carbonic 
acid ; and the result is, that the actual product of oxalic acid ob- 
tained represents only about one-half of the sugar employed, and 
therefore not above one-half the quantity which should have been 
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