280 J. H. Long — Polarization of Tartrate Solutions. 



If we calculate the theoretical rotation from this equation 

 much closer results will be obtained than are given in column 

 six of the above table, where only half as much carbonate was 

 supposed to take part in the reaction. These equations would 

 suggest an explanation of the behavior of solutions 9, 10 and 11, 

 on standing. We may suppose at first a condition of equilib- 

 rium reached in which HNaC0 9 or SbONaCOg exists in solution. 

 This equilibrium is destroyed by standing or by slight change 

 of temperature so as to liberate C0 2 and permit the Na 2 C0 3 

 formed to react on a fresh portion of the tartrate, giving fur- 

 ther reduction in the rotation. When the rotation finally 

 becomes constant quite different amounts of antimony may be 

 left in solutions of the same original strength, as shown in the 

 fourth column of the table, opposite numbers 5 and 11. The 

 amount of antimony finally precipitated and the rapidity with 

 which it precipitates seem to depend to some extent on the 

 mechanical agitation which the solution receives. 



Further light is thrown on the question of decomposition by 

 the experiments next to be explained. 



Experiments with sodium acetate and phosphate. 



As I have before shown, acetates decompose the potassium 

 antimony tartrate solution slowly in the cold but rapidly when 

 heated. A solution containing 5 grms. of crystallized sodium 

 acetate with 5 grms. of the tartrate in 100 c.c. gave, at 20°, 

 a = 25 0- 745, while one with 10 grms. of the acetate gave 

 a = 24°-676 instead of 28°-207. Later tests made with solu- 

 tions mixed at the boiling temperature gave these results for 

 the filtered solutions, represented by the curve D, where the 

 abscissas have ten times the value they have in the others : 



In 100 c.c. 

 Tartrate. Acetate. a D 



5 grms. 5 grms. v 22°'125 



5 10 ' 18°-140 



5 15 14°-892 



These solutions were found to be strongly acid and by sub- 

 jecting them to distillation I obtained a small amount of acetic 

 acid. The precipitates were analyzed and were found to have 

 the same composition as produced by the carbonate, viz : 

 Sb 2 3 . H 2 0. The reaction taking place is probably this : 



2KSbOC 4 H 4 9 . H„0 + 2NaCoH 3 2 =2KNaC 4 H 4 6 +SbA . H 2 + 



2HC 2 H 3 2 . 



As a further test I prepared a solution with 10 grm. of the 

 acetate and 5 of the tartrate and heated it for one hour on the 

 water bath. It was then filtered. The filtrate, after addition 



