584 



to the polarisation of N". 3 (P), where 3 cm' of 1,06 normal NaOH- 

 solution had been added. 1 milligrammolecule of m.- and p. -hjdrox}^- 

 benzoic acid compensates therefore the action of 2 cm^ of normal 

 NaOH-solution. 



To avoid every accidental deviation in the comparison, experiment 

 N". 6 (F') served, from which could be concluded once more that 

 in alkalic solution salicylic acid behaves as monobasic acid. 



The intensity of colour of the solutions, which with these experi- 

 ments (P) was observed after 21 hours was in rather good agree- 

 ment with these results. ^) 



In the above we have met a difference in properties of salicylic 

 acid on the one hand and the meta- and para-hydroxybenzoic acids 

 on the other hand, which is not expressed by the usual constitution- 

 formula: 



OH OH OH 



COOH |/^\ /\ 



\/COOH \/ 



COOH 



ortho meta para 



h y d r o X y b e n z o i c acid. 



Indeed this difference had been stated in other directions, viz. : 



l^f . The slight solubility of salicylic acid in water and the strong 

 solubility in oil.'') 



2"'*. The slight liability to attack of salicylic acid by organisms, 

 compared with the strong liability to attack of the meta- and para- 

 hydroxybenzoic acids.') 



3'"^. The antiseptical action of salicylic acid, which is strongly 

 connected with the properties mentioned under 1 and 2.^) 



Furthermore in such compounds the presence of hydroxy Igroups 

 increases the solubility in water and decreases the solubility in oil. 



Finally in many cases the augmentation of the number of 

 hydroxylgroups causes that the compounds can be attacked easier by 

 organisms. ^) 



These considerations necessitate to reject the usual constitution- 



^) It must be remarked that the observations of intensity of colour have no 

 absolute but only a relative value; the results of a series of experiments therefore 

 can only be compared mutually and not with experiments belonging to another 

 series. To a certain degree this is also the case with the polarisation because the 

 temperatures at the beginning of the experiments are not always the same but 

 depend on the temperature of the laboratory. 



2) J. BöESEKEN and H. I. Waterman, These Proc. November 25, 1911 p. 608. 



