1904.] KELLER AND MAAS — DIMETHYL RACEMIC ACID. 107 



characteristic crystalline precipitate. Its separation may be pro- 

 moted by the introduction of a few particles of the solid salt. 



The free acid is readily obtained from tliis barium salt by means 

 of sulphuric acid. The theoretical quantity of the latter, diluted 

 with water, is added to the finely powdered substance, and the 

 mixture heated with occasional stirring. When the decomposition 

 appears complete, the barium sulphate formed is filtered off, and 

 the filtered solution evaporated to crystallization. The dimethyl 

 racemic acid thus prepared generally forms large transparent crys- 

 tals, and is easily purified by repeated crystallizations. This pro- 

 cess of extracting the dimethyl racemic acid from the products of 

 the action of hydrochloric acid and diacetyl dicyanhydrin, is more 

 convenient and gives a better yield than that described by Fittig 

 and Keller. More than 60 grammes of material have been made 

 by its means. 



Properties of Dimethyl Raceifiic Acid. — The physical properties 

 of the acid have been accurately described by its discoverers, and 

 little can be added here to their description. Although remarkably 

 fine crystals have been repeatedly obtained, a definite determina- 

 tion of their form remains to be made. There is reason, however, 

 for believing that racemic acid is not isomorphous with its dimethyl 

 derivative. Contrary also to a previous statement, it has been 

 observed that when crystals of dimethyl racemic acid are kept for 

 a long time they do effloresce, though far more slowly than those 

 of racemic acid. 



The water of crystallization is completely expelled at 105*^, rede- 

 terminations of its amount gave 9.05% and 9.12 % ; theory requires 

 9.18%. Above 110° there is a further loss of weight, owing no 

 doubt to a slow decomposition of the molecule. 



The solution of dimethyl racemic acid in water, like that of other 

 synthetic compounds containing assymetric carbon atoms, is opti- 

 cally inactive. 



Salts of Dimethyl Racemic Acid. — With the very limited amount 

 of acid at their disposal, Fittig and Keller were able to prepare but 

 a small number of the salts, and three of these only were obtained 

 in a pure state and in quantities sufficient to permit analytical 

 determinations. The data thus secured were, however, sufficient 

 to confirm the composition of their acid, and to establish its close 

 analogy with the tartaric acids. At the same time certain anom- 

 alies in the composition and some of the properties of the dim- 



