310 PROCEEDINGS OF THE AMERICAN ACADEMY 



The observations recorded in this table divide these substances into 

 the following groups (indicated by the lines): — I. and II., most acid ; 

 III., IV., and v., less acid ; VI., less acid; VJI., less acid ; VIII., least 

 acid. The relative acidity of I. and II. was determined by data of the 

 second sort mentioned above, since I. gave a much stronger coloration 

 than II. with aqueous sodic carbonate, ammouic hydrate, or sodic hy- 

 drate. The order of III., IV., and V. was determined by the following 

 observations. With acid sodic carbonate and dilute alcohol. III. and 



IV. gave a stronger red color than V. With aqueous sodic carbonate, 

 III. gave a pale red, V. a much paler, in fact barely perceptible color. 

 With aqueous aramonic hydrate, III. gave a pale red, V. a very pale 

 barely perceptible red, and IV. stood between III. and V. in color. 

 With aqueous sodic hydrate, the color was confined to the crystals of 

 the organic substance, owing to the slight solubility of the salt in a 

 solution of sodic hydrate, and III. turned dark red, IV. pale red, while 



V. showed a mixture of pale red particles of the salt and white ones 

 of the ester. Upon adding alcohol to the mixture of the substance 

 and either aqueous sodic carbonate or ammonic hydrate, a dark red 

 color was obtained from all three, but much more alcohol was neces- 

 sary to produce this color with V. than with III. or IV. My obser- 

 vations on the intensity of the color with different reagents confirm 

 the order of compounds VI., VII., and VIII., but I do not think it 

 worth while to give the details. I should add, also, to show that the 

 personal equation did not enter to any great extent into these obser- 

 vations, that the substances during the experiments were arranged in 

 an order different from that of their acidity, and that the order of 

 acidity given above derived from these experiments was a surprise to 

 me in many particulars. 



These experimental results justify the following inferences in re- 

 gard to the effect of differences in composition upon the acidity of 

 these substances. 



(a.) The introduction of an additional nitro group (in the ortho 

 position) increases the acidity, since II. is more acid than III. 



(b.) The replacement of hydrogen (in the ortho position) by bro- 

 mine diminishes the acidity, since V. is less acid than III. 



(c.) Tlie replacement of bromine (in the meta position) by the 

 aniline radical CgH^NH reduces the acidity very considerably, since 

 III., IV., and V. are much more acid than VI., VIIL, and VII. 

 respectively. 



In all these cases the differences occur in the benzol ring, and the 

 effects are very marked (especially in c) when it is considered that 



