282 Pheljps and Eddy — Hydrobromic Acid. 



esterification that had not been removed under the conditions 

 of the experiment, when half of the alcoholic mixture had 

 acted upon the acid. It is, however, a striking fact that two 

 grams of sulphuric acid with half the amount of alcohol acting 

 about one-third of the same time with the same amount of ben- 

 zoic acid gives theoretical yields of ester. 



In the work recorded here the catalytic action of zinc bro- 

 mide and hydrobromic acid at different temperatures on ben- 

 zoic acid with ethyl alcohol is brought into comparison with the 

 similar action of zinc chloride and hydrochloric acid recorded in 

 the paper to which reference has been made, as well as in this 

 paper. 



For this work ethyl alcohol was prepared as free from water 

 as possible by repeated distillations with calcium oxide. The 

 benzoic acid used was the pure benzoic acid of commerce. For 

 the preparation of pure, dry hydrobromic acid the pure bro- 

 mine of commerce was freed from chlorine by long standing, 

 with frequent shaking, in contact with an aqueous solution of 

 potassium bromide,* before distilling off the bromine. The 

 hydrobromic acid gas was prepared by allowing the purified 

 bromine to act on a mixture of red phosphorus and water, the 

 gas set free being purified by passing first through layers of 

 moist red phosphorus and glass wool contained in one leg of a 

 U-tube, the outer leg of which, to dry the gas completely, con- 

 tained layers of phosphorus pentoxide and glass wool. The 

 hydrobromic acid thus prepared was dissolved in chilled alcohol 

 in the concentrations given in the tables. These concentra- 

 tions were chosen of such values that the hydrobromic acid in 

 these experiments was in molecular proportion to the hydro- 

 chloric acid in the experiments to which reference has been 

 made. Pure zinc bromine was prepared for use in two different 

 ways. The pure zinc bromide of commerce was fused in an 

 atmosphere of pure hydrobromic acid before granulating the 

 melted zinc bromide. Zinc bromide was also prepared by heat- 

 ing in a flask connected to a return condenser the pure zinc of 

 commerce at a temperature above the melting point of zinc 

 with bromide purified, as described above, for the preparation 

 of hydrobromic acid, and then dried with sulphuric acid before 

 distilling. The pure zinc bromide made in this way was melted, 

 as in the case of the commercial sample, in an atmosphere of 

 dry hydrobromic acid, heated to expel any excess of hydrobro- 

 mic acid, and then granulated. The amounts of zinc bromide 

 used corresponded molecularly to the zinc chloride used in the 

 esterification of benzoic acid in the work to which reference 

 has been made. 



In all the experiments given in this paper the procedure was 



* Kichards and Wells, Proc. Amer. Acad., xli, 440. 



