162 ODOROGRAPHIA, 
a Jong time, each being clearly distinguishable, and it is only 
after several months of contact that they unite or blend into a 
single odour, which is that of heliotrope. 
Vanillin forms white needles, generally occurring in stellate 
aggregates, which possess a very strong taste and smell of vanilla. 
It melts at 80°-81°, sublimes readily, boils at 285° C. without 
decomposition when heated in an atmosphere of carbon dioxide, 
and dissolves in 90 to 100 parts of water at 14° and in 20 parts at 
75°-80°. It is scarcely soluble in cold, more readily in hot petro- 
leum spirit. Its aqueous solution is coloured bluish violet by ferric 
chloride; if this solution be heated, white needles of dihydro- 
vanillin separate out. 
Glucovanillin is formed by the oxidation of coniferin with a 
dilute solution of chromic acid. It is readily decomposed by 
emulsin into grape-sugar and vanillin. 
Vanillin is frequently adulterated with benzoic acid to a very 
large extent. Upon treating such a mixture with dilute solution 
of sodium carbonate, the benzoic acid is dissolved and can be pre- 
cipitated from the solution by adding excess of water; or the 
filtrate, after neutralization with hydrochloric acid, will give with 
ferric chloride a red-brown precipitate of ferric benzoate. The 
acid, or the benzoate, can be reduced by means of sulphuric acid 
and magnesium ribbon to benzaldehyde, which is recognizable by 
its characteristic odour of bitter almonds *, 
Vanillin should be stored in well-stoppered bottles, as by ex- 
posure to a damp atmosphere it is converted into vanillic acid, 
which, when pure, is odourless. In the natural state as it exists 
in the pods the aromatic resmous substances with which it is in 
contact help to prevent this change; but it is always advisable to 
keep the pods in well-stoppered glass jars. 
Artificial Vanillin. 
The crystalline coating of vanilla pods (givre de vanille) was first 
prepared artificially by Tiemann and Haarmann from Coniferin 
(C,,H,,0,), which occurs in the cambium sap of the fir-tree and is 
decomposed by emulsin in the presence of water into grape-sugar 
and the compound C,,H,,0;, forming odourless crystals which, 
after standing in the air for some time, have a faint smell of vanilla. 
The investigators therefore oxidized coniferin with chromic acid, 
* Deutsch. Amerik, Apotheker-Zeitung, July 1888, p. 103, 
