Chemistry. — ''The double acid from normal- and allo-cinnamic 

 acids''. By A. W. K. de Jong. (Communicated by Prof. P. 

 VAN Romburgh). 



(Communicated in the meeting of January 26, 1918). 



This double acid can be piepared by well known methods, for 

 instance by allowing a solution, saturated at ordinary temperature 

 with respect to both acids, to crystallize slowly, or by dissolving 

 in such a solution equal quantities of the tw^o acids by heat, when 

 on cooling the double acid separates. 



It can be readily prepared from normal cinnamic acid as follows: 

 A dilute aqueous solution of sodium cinnamate (lOgrm. of cinnamic 

 acid per litre) is exposed to light in open tanks (at Buitenzorg about 

 3 months suffice for tanks of about 12 litres capacity and 500 cm' 

 surface, with illumination in the fore-noon only). The solution is 

 then evaporated to dryness; the acids are liberated by concentrated 

 hydrochloric acid and are separated from the sodium chloride by 

 hot motor spirit. The petrol solution often gives on cooling crystals 

 of /?-cinnamic acid, which on standing pass into the «-variety. After 

 cooling, the solution is exposed to the air in a dish. Generally 

 crystallisation begins soon and well formed, often rhomb-shaped 

 crystals of the double acid separate. On further evaporation of the 

 solution either crystals of alio cinnamic acid are formed, or this 

 acid separates as an oil. 



Since there exist two moditications of the normal acid, and three 

 are known of the allo-acid, it would be quite possible that several 

 different double acids should exist. 



Now it is not difficult to prepare a solution, saturated with 

 respect to both acids, which is at the same time in equilibrium with 

 one of the three different forms of allo-cinnamic acid. For this 

 purpose a warm concentrated solution of the two acids is prepared 

 and should then be boiled for ^1^ hour. The flask is plugged with 

 cotton wool, to prevent infection, and the contents are cooled, which 

 causes separation of the double acid, together with melted allo-acid 

 (the temperature here is 25 — 30°). This solution is in equilibrium 

 with allo-acid of melting point 42°. If the solution is inoculated 

 with allo-cinnamic acid melting at 58° or 68°, it soon crystallizes 



