ACETIC ALDEHYDE, ETC. 107 



at 43, which are decomposed by keeping. It is a 

 base, and yields crystallizing salts with acids. 



, The remaining aldehydes of this series are prepared 

 either by carefully oxidizing the corresponding alco- 

 hols with potassium bichromate and dilute sulphuric 

 acid, the apparatus being so arranged that the aldehyde 

 formed may distil over immediately ; or by subjecting 

 an intimate mixture of the calcium salt of the corre- 

 sponding acid with calcium formate to dry distillation. 

 To purify them and separate them from foreign sub- 

 stances, they are shaken with a concentrated solution 

 of potassium or sodium bisulphite. The aldehydes 

 combine with these substances, forming crystalline 

 compounds, which are difficultly soluble in cold water. 

 These are then pressed, washed with alcohol, or recrys- 

 tallized from a little warm water, and, finally, decom- 

 posed by distillation with a solution of an excess of 

 sodium carbonate, the pure aldehyde now passing over. 

 The most important aldehydes are the following: 



3. Propionic aldehyde, C 3 H 6 O = CH 3 .CH 2 .CHO. A 

 liquid, possessing a suffocating odor, very similar to 

 acetic aldehyde. Specific gravity, 0.8327 ; boiling point, 

 49.5. 



4. Butyric aldehyde, C 4 H 8 = CH 3 .CH 2 .CH 2 .CHO. 

 Colorless liquid ; specific gravity, 0.834 at ; boiling 

 point, 75 ; soluble in 27 parts water. 



Chlorbutyric aldehyde, C 4 H 7 C10. Is produced by di- 

 rect combination of crotonic aldehyde (which see) with 

 hydrochloric acid gas. Colorless needles ; fusing point, 

 96-97 ; insoluble in water, scarcely soluble in alcohol. 



Isobutyric aldehyde, C 4 H 8 = CH.CHO. Color- 



less liquid ; specific gravity, 0.8226 at ; boiling point, 



62. 



5. Normal valeric aldehyde, C 5 H 10 = CHACIP.CH 2 . 

 CIP.CHO. A liquid, boiling at 102. 



