OF SULPHURIC ACID UPON VARIOUS CLASSES OF VEGETABLES. 
469 
that crude furfurol always contains a considerable quantity of acetone, a circumstance 
which appears to have escaped the notice of preceding experimenters. 
In addition to the substances which had been previously employed for preparing 
furfurol, I may mention that I have obtained it from oil-cake, from cocoa-nut husk, 
and from the raspings of mahogany. The two first substances, from their cheapness 
and the large quantity of oil which they yield, are very well fitted for this purpose. 
The furfurol from mahogany, though smaller in quantity, is pretty free from resin, and 
is therefore more readily purified than that from bran or oil-cake. 
Crude furfurol, from whatever source it is prepared, always contains a quantity of 
another essential oil, which has a much higher boiling-point and does not form a 
crystallizable amide. This second oil is exceedingly oxidizable, and every time it is 
distilled a considerable portion of it is changed into a brownish resin, which instantly 
strikes a deep red colour when mixed with a few drops of cold muriatic, nitric or sul- 
phuric acids. In a previous paper I mentioned this reaction as characteristic of fur- 
furol, and in this statement I have been followed by Dr. Fownes. It is a mistake, 
however, as furfurol never yields this deep red colour with acids when it has been 
freed from this accompanying oil, which, as it appears to be invariably formed along 
with furfurol, I shall call meta-furfurol. 
Furfurol may be pretty readily freed from this oil by being repeatedly rectified with 
water ; the meta-furfurol, as it is much less volatile, remains chiefly in the retort, where 
it is rapidly oxidized. Two, or at most three rectifications, are therefore sufficient to 
render furfurol perfectly free from meta-furfurol. The absence of meta-furfurol may 
be easily ascertained by boiling an aqueous solution of furfurol with an excess of lime 
for a few minutes. The furfurol is immediately oxidized, and the solution acquires a 
deep yellow colour. If this solution is then treated with an excess of muriatic or 
sulphuric acids, not the slightest reddening is produced if the furfurol is free from meta- 
furfurol, but if even a trace of this latter oil is present, the characteristic deep red 
colour immediately appears. When pure furfurol is added to strong muriatic or sul- 
phuric acid in the cold, it instantly changes to a brownish black colour, being rapidly 
oxidized, but not the slightest reddening is visible. Meta-furfurol is also much less 
soluble in water than furfurol. It also dissolves with difficulty in aqueous ammonia, 
with which it forms no crystallizable amide, but is rapidly changed into a brownish 
amorphous resin. When meta-furfurol is digested with strong nitric acid, it is changed 
into a nitrogenated crystallizable acid, which is either oxypicric acid, or a closely 
analogous compound. It yields chloropicrine when it is treated with either muriatic 
acid or hypochlorite of lime. Furfurol, on the contrary, when digested with nitric 
acid, is wholly converted into oxalic acid. Crude furfurol made from bran contains 
a good deal of meta-furfurol, but the crude furfurol from mahogany and other hard 
woods is comparatively free from meta-furfurol. 
Furfurol stains the skin of a deep yellow colour, but if the part moistened with it 
is also touched with a few drops of aniline it becomes of a bright red colour. The 
