THE ETHYL-SULPHURIC ACID REACTION. 385 



when the reaction is complete. The degree of completeness of the reaction 

 at any time can therefore be measured by titration of the reaction mixture 

 with standard alkali, if there are no complications due to other reactions, 

 This was the method followed, and methyl orange was used as the indicator. 

 Regarding complications due to other reactions, it might be feared that dilu- 

 tion of the mixture before titration might reverse the reaction appi-eciably 

 before the neutral point was reached, and the significance of the titration 

 results be thus impaired. Also, disappearance of acidity might be due in 

 appreciable measure to the reactions shown in equations (D), (E) and (F). 



To determine the first point, titrations were made at various time intervals 

 after dilution, and it was foimd unexpectedly that no increase in acidity oc- 

 curred even in twenty-four hours. This was surprising, considering the 

 rapidity of the reaction in the other direction (as will be shown), and the 

 fact that the conditions of equilibrium reached were found to be approximately 

 equivalent to half completeness in the original direction. There is apparently 

 some marked auto-catalytic effect involved. 



The essential correctness of the assumption that the completeness of the 

 ethyl-sulphuric acid reaction was really measured by the titration was con- 

 firmed by actually isolating the product in the form of its potassium salt, 

 as follows: To the mixture was added calcium carbonate as long as effer- 

 vescence resulted, converting both the ethyl-sulphuric acid and the unchanged 

 sulphuric acid into their calcium salts; the calcium sulphate was then 

 filtered out and washed, and to the filtrate containing calcium ethyl-sulphate 

 potassium carbonate solution was added until the precipitation of calcium 

 carbonate was just complete; the filtrate from this was evaporated to dryness, 

 and the potassium ethyl-sulphate weighed. The yield corresponded in one 

 ease to a 57 per cent completeness of reaction as compared with 59 per cent 

 by the titration method for the same conditions; in another ease the yield 

 indicated a completeness of 60.9 per cent, and the titration one of 60.0 per 

 cent. 



To determine the speed and completeness of the original reaction, as 

 shown by equation (A), the procedure was as follows: Equal molecular 

 quantities of absolute alcohol and pure sulphuric acid were mixed, with 

 precautions as to cooling to prevent a rise in temperature above that for 

 which data were sought; it was found practicable to obtain satisfactory 

 results at temperatures ranging from 20 to 140° C. The mixture was kept 

 in a bath of water or sulphuric acid maintained at a constant temperature; 

 duplicate samples were withdrawn at intervals, diluted with water, and ti- 

 trated with standard sodium hydroxide. 



Results. 



The results obtained may be briefly stated as follows: The completeness 

 of the reaction ranged f;-om 58 per cent at 20° to a maximum of 60.4 per 

 cent at 50°, and to 42.6 per cent at 140°, as calculated from the titrations, 

 being almost constant, at 58 to 60.4 per cent, from 30° to 90°. 



