A Manual of the Chemistry of the Carbon Compounds

412 THE CHBMI8THY OF
Pare aurin is also readily obtained by heating pure phenol with
oxalic acid and sulphuric acid for several days to 100°—110*. The
product is boiled with water, dissolved in caustic soda, and precipitated
with an acid. The crystalline precipitate is then crystallized
from alcohol
Aurin is also obtained by using formic acid in the place of oxalic
acid, and its formation may therefore be expressed by the equation: —
SC0H0O + 200 = CjjHyOg + 2HjO
When sulphur dioxide is passed into a hot concentrated alcoholic
solution of auriu, the compound (CJDH^OJJJSOJ + 5H2O is formed,
separating on cooliug hi brick-red orusts, or garnet-red granular
crystals.
Aurin-potamum, Sulphite CMH,4O8 4- KHSO3 is obtained by adding
a solution of acid potassium sulphite to a hot alcoholic solution ot
aurin. It is a crystalline white powder, resembling precipitated
chalk. The sodium and ammonium-compounds are similar bodies;
they are easily decomposed by acids and alkalis.
Leucwiirin CMH1(}08 is formed by heating an aqueous alkaline or
acid alcoholic solution of aurin with zinc-dust. It crystallizes in
thick colourless prisms or needles. It contains three hydroxyls,
yielding with acetyl chloride tri-acetyldmcanrin CJQHJJOJ^JHJOJJ,
crystallizing from alcohol in white silky needles.
JPIwnol-pntJMlein CLH14O. is produced by heating phenol with
phthalic anhydride and sulphuric acid to 120°.
C8H4Os = C49HHO4 + HaO
It is a colourless body, dissolving in caustic potash with a splendid
red colour, which disappears on heating it with xinc-dnat. Hydrochloric
acid precipitates from the colourless solution plimol-pkthalin
C^H,^ hi white granular crystals.
Fluorescdii, or Besortin-phthaMn CWH,8O,, is formed by heating
resorcin with phthalic anhydride. It forms small dark-brown crystals,
dissolving in ammonia with a red colour; this solution exhibits, even
when very diluted, a most beautiful green fluorescence. Zinc-dust
reduces it to colourless fliutrescin, and by heating it with sulphuric
acid it is converted into a red compound, dissolving in alkalis with a
blue colour, which, on adding zinc-dust, changes into red.
ffydrogwhonc-jihthakin. CMH,206 is obtained by heating hydroquinone
with phthalic anhydride and sulphuric acid; it forms white
crystals, melting at 232°, and dissolving in alkalis with a violet
colour.
Gallein C^H^Oy has been produced by heating pyrogallol with
phthalic anhydride. It forms granular crystals, appearing brownishred
by reflected light, and blue by transmitted light. It dissolves in
alcohol with a dark-red, and in alkalis with