242 
ON THE MANUFACTURE OF OXALIC ACID. 
Instead of cane-sugar or treacle, the saccharine substance form- 
ed by the action of sulphuric acid on potato or other starch (as in 
Mr. Nyren's process) is employed. For this purpose the potatoes 
are well washed, and then reduced into a fine pulp by rasping, 
grinding, and other suitable means ; such pulp is then washed two 
or three times by placing it in water and well stirring it therein, 
then permitting the pulp to subside, and running off the water. 
The pulp thus obtained is next placed in an open vessel of lead, 
or wood lined with lead, with as much water as will allow of the 
mixture being boiled freely by means of steam passed through 
leaden pipes placed therein. Into the mixture of pulp and water 
about 2 per cent, by weight (of the potatoes employed) of sulphu- 
ric acid is to be stirred in, which will be at the rate of from 8 to 
10 per cent, of acid on the quantity of farina contained in the po- 
tatoes ; the whole is now to be boiled for some hours until the 
pulp of the potatoes is converted into saccharine matter ; the com- 
pletion of this process being readily ascertained by applying a 
drop of tincture of iodine to a small quantity of boiling liquor 
placed on the surface of a piece of glass, when, if there be any 
farina remaining unconverted, a purple color will be produced. 
The saccharine product thus obtained is then filtered through a 
horse-hair cloth, after which it is carefully evaporated in any con- 
venient vessel until a gallon of it weighs about 14 or 14| lbs. It is 
now in a proper condition to be employed in the manufacture of 
oxalic acid, by the application of nitric acid, as in the case of ope- 
rating upon sugar or treacle. Horse-chestnuts, deprived of their 
outer shells, are also applicable to the manufacture of oxalic acid 
when treated in the way above described for potatoes. 
Instead of operating with sulphuric acid, the farina of potatoes 
and of chestnuts may be treated with diastase, and converted into 
a liquor similar to that obtained after evaporation from the farina 
and sulphuric acid before mentioned, using about the same pro- 
portion of diastase as above directed for sulphuric acid. In this 
case the liquor is made of the required strength at once, and the 
processes of filtration and evaporation are rendered unnecessary. 
The apparatus required in the conversion of the saccharine mat- 
ter (whether of cane-sugar or formed of starch in the way above 
mentioned) into oxalic acid is very simple. Usually, earthenware 
jars of about two gallons capacity, are employed, which, when 
