242 HALOIDS AND HALOID BASES. 



duced, according to Berzelius,* on heating 1 part of glycerine, dried 

 at 120, with 2 parts of dry tartaric acid; it is a semi-solid trans- 

 parent body, which is solid at 0, but at 25 admits of being drawn 

 out in long threads ; it deliquesces in the air, does not dissolve in 

 alcohol, and with bases forms soluble uncrystallisable double salts, 

 which are readily decomposed by an excess of base. The relations 

 of biracemate of glycerine are similar to those of this salt. 



Products of its metamorphosis. Acrolein, C 6 H 4 O 2 , discovered 

 by Redtenbacher,t is obtained from glycerine by submitting it to dry 

 distillation with a little anhydrous phosphoric acid in a stream of 

 dry carbonic acid gas ; the distillate, consisting of a thick oil, of 

 an acid fluid swimming on it, and of acrolein floating on the 

 latter, must be digested with oxide of lead and distilled at 52 into 

 a receiver containing carbonic acid, by which means we obtain the 

 acrolein. It is an oily fluid, which strongly refracts light, has an 

 acrid, burning taste, irritates the eyes and respiratory organs, and 

 forms a neutral solution in water devoid of air, which, however, very 

 soon assumes an acid reaction on exposure to the atmosphere. 

 It instantly reduces oxide of silver, and it decrepitates b h with 

 nitric acid and with potash. 



Acrylic acid, C 6 H 3 O 3 + HO, is formed when acrolein is 

 oxidised either by exposure to the air or by oxide of silver ;it is a 

 limpid fluid, with an odour resembling that of very strong acetic 

 acid, and a pure, acid taste ; nitric acid converts it into acetic and 

 formic acids ; it forms soluble, crystallisable salts with bases. 



Disacrone, disacryl, C 10 H 7 O 4 , is gradually deposited from acro- 

 lein exposed to the atmosphere ; it is idio-electric, devoid of 

 odour and taste, and insoluble in all menstrua. 



Preparation. Glycerine is formed, as we have already men- 

 tioned, during the saponification of the fats, from the oxide of 

 lipyl contained in them combining with 4 atoms of water. It is 

 usually prepared from the aqueous fluid which separates during the 

 preparation of lead- plaster, and contains it, together with oxide of 

 lead, in solution. After the removal of the lead by sulphuretted 

 hydrogen we concentrate the solution first in the water-bath and 

 subsequently in vacuo. We may also obtain it from the mother- 

 liquid yielded in ordinary saponification by the alkalies, on satu- 

 rating the alkali of the ley with sulphuric acid, then heating it with 

 carbonate of baryta, evaporating the filtered fluid, and extracting 

 with alcohol. It may be obtained very readily, and in a state of 



* Jahresber. Bd. 27, S. 438. 



t Ann. d. Ch. u. Pharm. Bd. 47, S. 113-148. 



