ALDEHYDE. 781 



To prepare aldehyde, a mixture is distilled by a gentle heat of 

 6 parts of sulphuric acid, 4 parts of water, and 4 parts of recti- 

 fied spirits of wine, and the product carefully condensed, so long 

 as chemical action appears to take place from the frothing up 

 of the materials in the retort. The distilled liquid, which is a 

 mixture of aldehyde with water and several other secondary pro- 

 ducts, is distilled by a water- bath from an equal weight of chlo- 

 ride of calcium, till one half of it passes over. But to free the 

 aldehyde from foreign bodies, it is necessary to unite it with 

 ammonia ; the product of the last distillation is therefore diluted 

 with an equal volume of ether, and the mixture saturated at a 

 low temperature with ammoniacal gas ; the compound, or am- 

 monia-aldehyde is deposited in colourless crystals, which are 

 afterwards washed with ether and dried in air. Two parts of 

 ammonia-aldehyde dissolved in 2 parts of water are distilled 

 with 3 parts of sulphuric acid diluted with 4 parts of water, and 

 the product condensed in a receiver surrounded with ice. It is 

 afterwards rectified from chloride of calcium, by a heat not ex- 

 ceeding 77 or 86 (25 or 30 cent.). 



Aldehyde is a colourless, highly-fluid liquid, of a peculiar 

 ethereal and suffocating odour, boiling at J\..6 (22 cent.) of 

 density 0.790 at 64.4 (18 cent.), neutral, and very combustible. 

 It is miscible with water, alcohol and ether. It changes in the 

 air into acetic acid by absorption of oxygen. It dissolves phos- 

 phorus, sulphur and iodine. 



When pure and anhydrous aldehyde is kept for some time 

 at 32, it gradually loses its power to mix with water, and is 

 transformed into a coherent mass, composed of long transparent 

 needles, resembling icy spiculse. This is Elaldehyde, which is 

 similar in composition to aldehyde, but of three times the atomic 

 weight, judging from the density of its vapour. Elaldehyde 

 fuses at 35.6 (2 cent.), and boils at 201.2 (94 cent.). 



Metaldehyde is another product of the condensation of the 

 elements of aldehyde, which appears at the ordinary temperature 

 in aldehyde left for some time in a well-stopped phial, in the 

 form of white and transparent needles, or colourless prisms, 

 which gradually attain a certain magnitude. It sublimes at 

 248 without fusing, and condenses in the air in snowy and very 

 light flocks. It is insoluble in water, but dissolves easily in 

 alcohol. The density of its vapour has not been determined. 



