192 FSOCEEDINGS OF THE aXEP.ICaN ACADEMY 



gave as its mean value lO-t" 17. Reboul gives the same angle in 

 crvsials of pentabromethan as 104r 20'. and Bourgoin as 104" 16 . 



The idendtr of the substance was still further established by 

 analysis* 



0.11-51 grm. substance gave 0.2547 grm. AgBr. 



Caknjased Sir CMBr^. Fonni. 



Br 9il2 94.17 



After we had proved that malonic acid was one of the final products 

 of the decomposition of mucobromic acid when boiled with an excess 

 of baric hydrate, we attempted, by various modifications of the mode of 

 decomposition, to isolate intermediate products, which might give us 

 infi^rmation concerning the nature of the reaction. After many 

 unsuccessful experiments, we foimd that such products resulted from 

 the action of alkalies at ordinary temperatures, and they were most 

 conveniently studied when baric hydrate was employed. 



Baric Dibromacn/late. Ba(CjH Br^O^\. If mucobromic acid is gradu- 

 ally addei to a solution of baric hydrate containing a large excess of 

 baric hydrate in suspension, it dissolves readily, and the crystals of 

 baric hydrate at the same time gradually disappear. After a while a 

 beautifully crystalline barium salt begins to separate, the amount 

 of which increases rapidly as the acid is added. In order to prepare 

 this salt, we found it best to add the mucobromic acid until one mole- 

 cule had been used for every one and a half molecules of baric 

 hydrate. At first we used two parts of crystallized baric hydrate and 

 four of water to one part of mucobromic acid, but subsequently we re- 

 duced the amount of water one half. After the necessary amount of 

 mucobromic acid had been added in small portions, care being taken 

 to prevent any elevation of temperature, the whole was allowed to 

 stand for a short time, and the crystals which had separated were 

 then filtered off on the pump. These were washed with a little cold 

 warer. exposed to carbonic dioxide imtil neutral in their reaction, 

 and then recrystallized from water or diluted alcohoL From alcohoL 

 the salt crystallized in pearly rhombic plates : from water, in irregular 

 leafy forms, or, on slow evaporation, in massive aggregates of rhombic 

 plates. When dried by exposure to the air, they lost nothing over 

 sulphuric acid or when heated to 80^. At 100^ they slowly lost 

 in weight. 



The air-dried salt gave on analysis the percentages required by the 

 barium salt o£ a dibromacrylic acid. 



