20 Dr. Bevan Lean on the 



the solution of these acids in potassium hydrate, which, as 

 shown by phenol phthalei'n, has been neutralised by hydro- 

 chloric acid, a distinctly blue coloration is produced. On 

 adding more hydrochloric acid, the blue coloration changes 

 gradually to a red tint, and the solution appears to become 

 really neutral only when sufficient hydrochloric acid has 

 been added to neutralise one half of the potassium hydrate, 

 which was equivalent, as shewn by phenol phthalei'n, to the 

 tetracarboxylic acid present. 



In view of these results, obtained in determining the 

 basicity of the acids, it appeared of interest to examine 

 some of their salts. While the silver and calcium salts 

 prepared in the usual way from dimethyl and diethyl- 

 butanetetracarboxylic acid are found to be tetrabasic, those 

 prepared from dibenzylbutanetetracarboxylic acid are found 

 to have the formulae C 22 H2o0 8 Ag2, and C22H 2 o0 8 Ca + 2 H 2 

 respectively ; so also the salts prepared from dicetyl- 

 butanetetracarboxylic acid are found to be dibasic. 



On the different behaviour of Indicators. 



By these observations is brought out, in the first place, 

 the fact of the different behaviour of indicators towards one 

 and the same acid. It has been shown that the tetrabasic 

 potassium salts of dimethyl-, diethyl-, and dicetyl- butanete- 

 carboxylic acids are neutral to phenol phthalei'n, but 

 alkaline to litmus, and in titrating these acids with litmus 

 the final colour-changes are very indefinite. 



To illustrate further the different behaviour of indi- 

 cators, reference may be made to a systematic investigation 

 of the use of litmus, methyl-orange, and phenol-phthalei'n 

 as indicators, which was carried out by Smith 1 in 1883. 

 The following table, compiled from his results, shows the 

 character of the final colour-changes with several organic 

 acids : — 



1 Smith, Chem. News, 47-136. (1883). 



