128 ACROLEIN. 



Linoleic acid (C 16 H 28 2 ?), in linseed oil, and ricinie 

 acid, C 18 H 34 3 , in castor oil, are similar to, but not 

 homologous with, oleic acid. Both are contained in 

 the oils as glycerin compounds, and are prepared by 

 saponifying the oils and decomposing the alkali salts 

 with hydrochloric acid. Ricinie acid can be purified 

 by dissolving its lead salt in ether. It is an almost 

 colorless liquid, congealing at ; not volatile without 

 decomposition. Like oleic acid, it is transformed into 

 an isomeric, crystalline acid, ricinela'idic acid, fusing at 

 50. Conducts itself towards bromine like oleic acid. 



D. ALDEHYDES, C n H 2n ~ 2 0. 



1. Acrolein. 

 C 3 H 4 = CH 2 :CH.CHO. 



Formation and preparation. From allyl alcohol by 

 careful oxidation ; by the distillation of glycerin and 

 the fats. Can be most readily prepared by distilling 

 1 part glycerin with 2 parts potassium bisulphate. 



Properties. Colorless liquid, the vapor of which 

 attacks the eyes and nose violently. Boiling point, 

 52. Lighter than water and but slightly soluble in 

 it. "When kept it becomes changed, sometimes in a 

 very short time, into a white, amorphous substance. 

 It forms no crystallizing compounds with alkaline 

 bisulphites ; with nascent hydrogen it yields allyl alco- 

 hol. Alkalies convert it into a resinous mass. It 

 combines directly with hydrochloric acid, forming 

 C 3 H 5 C10 (colorless needles, fusing at 32, insoluble in 

 water), which, when subjected to distillation, are con- 

 verted into acrolein and hydrochloric acid. 



Metacrolein (polymeric acrolein, probably C 9 H 12 3 ) 

 is formed when the compound of acrolein with hydro- 

 chloric acid is distilled with caustic potassa. Colorless 

 crystals ; fusing point, 50 ; boiling point, 170 ; insolu- 

 ble in water, easily soluble in alcohol and ether. When 

 distilled it is partially reconverted into acrolein. 



