J. R. Long — Polarisation of Tartrate Solutions. 281 



of phenol-phthalein, was titrated with half normal KOH, of 

 which exactly 30 c.c. was required to give color. This is the 

 volume needed to neutralize the acid or precipitate the anti- 

 mony of the last equation. The solution remained quite clear 

 until about 12 c.c. of the alkali had been added, when it be- 

 came opalescent and finally turbid before the color reaction ap- 

 peared. In an experiment with 5 grms. of the tartrate in cold 

 solution without the acetate exactly the same amount of alkali 

 was required for coloration, but an opalescence appeared im- 

 mediately, and no actual precipitation occurred until all the 

 alkali had been added. This experiment amounts, of course, 

 to a titration of the tartrate : 



2KSbOC 4 H 4 6 + 2KOH=K 2 C 4 H 4 6 +Sb A • H 2 0. 



Finally, the experiment was varied in this way. 5 grms. of the 

 tartrate and 10 of the acetate were dissolved and mixed at a 

 low temperature. Phenol-phthalein was added and then alkali 

 to coloration. JSTow, as before, 30 c.c. was required to give color, 

 but the reaction took place in a different manner, as a precipi- 

 tate formed immediately and grew heavy as more alkali was 

 added. This behavior seems to indicate that the antimony is 

 held in a peculiar manner, partly at least, in the solution con- 

 taining the acetate. Possibly a preliminary reaction is this : 



KSbOC 4 H 4 6 +NaC 2 H 3 2 =KNaC 4 H 4 6 4-SbOC 2 H 3 2 , 



the last being stable in cold dilute solution but decomposed by 

 heat or alkalies, 



2SbOC 2 H 3 2 +2KOH=2KC 2 H 3 2 +Sb 2 3 . HX>. 



If the above equations express the truth we can readily 

 account for the polarization phenomena. In fresh solutions 

 prepared in the cold the rotation is decreased because of the 

 abstraction of a part of the antimony to form acetate. In the 

 boiled solutions, or in those prepared cold, after long standing, 

 the rotation may be still further reduced by the action of free 

 acetic acid on the tartrate. Some results obtained with solu- 

 tions of sodium phosphate are given below : 



In 100 c.c. 



a D 



a D 



Tartrate. 



Phosphate. 



3 hrs. 



72 hrs. 



5 grms. 



0-2 grm. cold. 



27°'350 



27°-345 no ppt, 



5 



0-4 



26°'700 



26°-727 



5 



0-7 



25°-732 



25°-690 



5 



1-0 



24°-755 



24°\350 



5 



1*5 boiled 



21°-303 





5 



2-0 



19°-448 





5 



5-0 



11°'502 





