OP ARTS AND SCIENCES. 243 



size of the surface of contact ; and therefore no constant results can 

 be expected. I have confirmed these observations, while studying 

 the action of water on the substituted benzylbromides, as will be de- 

 scribed later in this paper. Under these circumstances, alcohol seemed 

 to be the only solvent admissible ; but its use introduced a new source 

 of error, since it acts on the benzylbromides, forming the correspond- 

 ing ethyl ethers and liydrobromic acid, as is shown by the following 

 experiment. 



Some parabrombeiizylbromide was boiled with absolute alcohol for 

 fifteen minutes. After removing the organic matter by precipitation 

 with water and filtration, a precipitate was formed on the addition of 

 argentic nitrate. 



This defect was removed as completely as possible by taking pains 

 that the benzylbromides should be in contact with the alcohol for the 

 same length of time in each series of experiments. Then the results 

 depended, in each case, on two reactions, viz. : — 



CfiH.XCH.Br + NaaHgO., = CgH^XCH^C^H^O^ + NaBr 

 C6H,XCH,Br + aH.OH = CgH^XCH^OC^Hs + HBr 



but, as the time of each was the same in all the experiments of a 

 series, the occurrence of the second did not materially affect the result, 

 especially as the amount of substance entering into this second reac- 

 tion was very small. 



The adjustment of the amount of alcohol to be used was no easy 

 matter, because sodic acetate and bromide are very sparingly soluble 

 in absolute alcohol, and any considerable dilution interferes with the 

 solubility of the benzylbromides; nor could the difficulty be removed 

 by increasing to any great extent the amount of alcohol, as this would 

 have increased the length of time necessary to stop the reaction. 



More important than any of the sources of error yet mentioned is 

 that proceeding from the differences in volatility of the benzylbromides 

 with alcohol vapor, since this must alter the amount of substance 

 capable of entering into the reaction in each case by the quantity of 

 bromide volatilized with the alcohol in the upper part of the flask ; 

 and it is principally to this cause, which I could find no way of remov- 

 ing, that I am inclined to ascribe the considerable variations in my 

 results. 



This discussion of the defects in the process shows that no absolute 

 agreement in the numbers obtained can be expected ; but they agree 

 nearly enough to establish certain interesting relations between the 

 rates of decomposition of some of these compounds. 



