e:\ipyreumatic oils, etc. 391 



produced by boiling any kind of madder with solution of 

 aluminium sulphide. 



Crude furfurol prepared by any of the above processes requires 

 to be rectified to purify it from Mdafurfurol, with which it is 

 always contaminated. The purity of the product may be tested 

 by boiling an aqueous solution of the furfurol for a few minutes 

 with caustic potash, and treating the dark yellow liquid with 

 excess of sulphuric or hydrochloric acid. If metafurfurol is 

 present, a deep red colour is produced ; if not, the colour remains 

 unchanged. 



When recently prepared, Furfurol is an almost colourless oil, 

 but it gradually changes by contact with the air, becoming darker 

 even in the dark, and ultimately blackening. Under water these 

 changes take place quickly. Pure Furfurol, which will not alter 

 by keeping, can only be obtained by repeated rectification. It 

 possesses great refractive power. Its odour resembles that of a 

 mixture of cinnamon or cassia, and bitter almonds. Its taste is 

 agreeable, resembling that of cinnamon. It has the property of 

 staining the skin yellow. Its sp. gr. is 1-648 at 15^-6 C. Boiling 

 point, 162'-^-8 to 16o^-o C. with the barometer at 29-9.* Stenhouse 

 stated the boiling point at 166^,t and its solubility in 11 parts of 

 water at 13^0. Fow^nes states it to be soluble in 12 parts of w^ater 

 at 15^-6 C. It is very soluble in alcohol. It volatilises unchanged, 

 and is very infiammable, burning with a yellow, very smoky tiame. 

 It is related to Pijromucic acid in the same way as common 

 aldehyde is to acetic acid. It likewise exhibits the characters of 

 an aldehyde in combining with acid sodium sulphite. 



A somewhat analogous product can be prepared by distilling 

 certain marine alge« (fuscus vesiculosiis, f. nodosus and f. serraUts) 

 with dilute sulphuric acid. The resulting oil has the same com- 

 position and odour as furfurol, but it is a less stable body. 



Metacetone. An oil occurring among the products of the 

 dry distillation of sugar, starch, gum or mannite with lime. It 

 also occurs among the volatile oils formed by the destructive 

 distillation of wood. Fremy prepared metacetone by gently 

 heating an intimate mixture of at least 500 grammes of sugar w^ith 



* Fownes, Phil. Trans., 1845, p. 253. 



+ Phil. Mag. [3], xviii., p. 132 ; xxxvii., p. 226. 



