EMPYREUMATIC OILS, ETC. 389 



condenser, a stronger heat is applied. As soon as sulphurous acid 

 gas commences to be disengaged, 500 grammes of water are to be 

 poured in upon the mass, and the distillation continued until the 

 gas is given off in larger quantity. The distillate which has then 

 passed over is put back into the retort, and the heat continued until 

 half of the quantity of liquid which was in the retort has passed 

 over. The product is then neutralised with calcic hydrate and re- 

 distilled. A heavy yellow oil then passes over, and a further 

 portion may be obtained by rectifying the aqueous portion, which 

 distils at the same time. The oil is dried over calcic chloride and 

 finally rectified. In subsequent experiments, Fownes obtained by 

 distilling 64 ozs. troy of wheat-bran, with 33 ozs. sulphuric acid, 

 and an equal volume of water, 1 oz. of furfurol ; and from 64 ozs. 

 of wheat-flour treated in the same manner, Ih dram, of impure 

 furfurol. 



5" — Cahours found that in preparing this oil, the proportion of 

 sulphuric acid could be advantageously diminished : — 6 kilos of 

 bran, 5 kilos of sulphuric acid and 12 litres of water are mixed in 

 a capacious still, and distilled till a strong odour of sulphurous acid 

 is emitted. The distillate is partially and repeatedly rectified over 

 calcic chloride. The yield in this way is 158 grammes of furfurol, 

 equal to 2*6 per cent of the weight of bran used, but part of this 

 yield is held in solution in the watery distillate, from which it 

 may be precipitated by ammonia in the form of Fui'furamide* 



Crude furfurol always contains acetone and another oil (meta- 

 furfurol), which, is very liable to rapid oxidation and resinification. 

 These are easily removed by rectitication. The product obtained 

 from mahogany sawdust is purer than that obtained from bran or 

 the husk of linseed. 



To save the repeated rectifications, the first distillate may be 

 immediately saturated with ammonia, the mixture set aside for 24 

 hours in a cool place and shaken occasionally. The furfuramide 

 which separates is then to be distilled with dilute hydrochloric 

 acid (not in excess), and the distillate rectified over chloride of 

 calcium (Doebereiner). 



6^^ — According to Stenhouse, a very advantageous process is to 

 distil bran with more than half its weight of sulphuric acid 



* Cahours, Ann. Cliim. Phys, [3], xxiv., p. 277. 



