1867.] 



Dr. Hofmann on Methylic Aldehyde. 



157 



more than once induced me to attempt the preparation of methyl-aldehyde, 

 but it was only at the conclusion of my last summer course that I succeeded, 

 to a certain extent at all events, in attaining the object of my wishes. 



A substance possessing the composition and the properties of methylic 

 aldehyde is formed with surprising facility if a current of atmospheric air, 

 charged with the vapour of methylic alcohol, be directed upon an incan- 

 descent platinum spiral. 



The bottom of a strong three-necked bottle, of two litres' capacity, is 

 covered to the height of about five centimetres with moderately warm me- 

 thylic alcohol. The first neck is provided with a tube descending to the 

 very surface of the liquid ; into the second is fixed a loosely-fitting cork, 

 which carries the platinum spiral ; the third one, lastly, communicates with 

 the upper end of a condenser, the lower end of which is fastened into a two- 

 necked receiver. This receiver is in its turn connected with a series of wash- 

 bottles, and the last of these communicates with a water-jet aspirator, by 

 which a current of air can be sucked through the whole system. 



The apparatus being disposed in this manner, the platinum spiral is 

 heated to redness and introduced into the three-necked bottle. After a 

 few minutes the flameless combustion of the methyl-alcohol begins to mani- 

 fest itself by the evolution of a vapour powerfully affecting the nose and 

 eyes. Gradually the temperature of the apparatus rises, and soon droplets 

 of a colourless liquid are condensed in the receiver. The formation of 

 methyl-aldehyde is now fairly proceeding, and if the current of air be 

 appropriately adjusted, the platinum spiral remains incandescent for hours 

 and even for days. There is no difficulty in collecting from 50 to 100 

 grammes of a liquid rather rich in methyl-aldehyde. 



Instead of establishing the current of air by a water-jet aspirator, a pair 

 of bellows may be conveniently employed. I have often used with advan- 

 tage the bellows of an ordinary glass-blowing table. This mode of pro- 

 ceeding is more particularly adapted to the requirements of the lecturer, 

 who is thus enabled, by simply accelerating the movement of the foot, to 

 enliven the combustion, so as to keep the whole spiral in a state of incan- 

 descence. By thus proceeding it happens, however, occasionally that the 

 gaseous mixture in the three-necked bottle is fired ; but these explosions 

 are perfectly harmless, the whole effect being the forcible ejection of the 

 loosely-fitting cork which carries the platinum spiral. 



The liquid which is being collected in the receiver has all the properties 

 which theory assigns to the aldehyde of the methyl-series, or, more properly 

 speaking, to its methyl-alcoholic solution. When rendered slightly alkaline 

 by a few drops of ammonia, and mixed with nitrate of silver, it yields, on 

 gently warming, a silver mirror of irreproachable perfection, which is in- 

 deed more readily and more certainly produced than with the aldehyde 

 of the ethyl-series. The reduction in this case is the result of two conse- 

 cutive reactions ; in the first stage the aldehyde yields formic acid, which 

 in the second stage is converted into water and carbonic acid. 



n2 



