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



weights as our basis we take equal numbers of molecules, we 

 obtain the following values representing the molecular rotation 

 of the three salts, 



K 2 C 4 H 4 6 = 64-42 



KNaC 4 H 4 6 = 62-34 



Na 2 C 4 H O = 59-85 



2 4 4 6 



from which it is apparent that the conversion of 20 gm of 

 Rochelle salt into the neutral potassium tartrate would give a 

 solution with increased rotation, while conversion into sodium 

 tartrate would give a solution with diminished rotation. On 

 this assumption the change can be accounted for in part, but 

 only in part. Taking the rotation for the mixture of 20 gm of 

 KtfaC 4 H 4 O e . 4H 2 with 20* m of KC1, given in the table above, 

 we have a = 9° -372. Now, considering this as produced by 

 16-03 gm of K 2 C 4 H 4 0— the equivalent of 20 gm of KNa0 4 H 4 0, . 

 4H a O — we obtain a specific rotation, 



[a] = 29°-23, 



which is too much, Landolt's value being 2848. 



In the same way taking the rotation a = 7°'900 found for 

 the solution containing 20 gm of KNaC 4 H 4 6 . 4H 2 and 20 gm of 

 NaCl and supposing this rotation produced by 13*76 gm of 

 Na 2 C 4 H 4 6 we find the specific rotation, 



[«] = 28-70, 



which is too low, or, in other words, too great a reduction, 

 Landolt's value being 30*85. 



It will be seen, however, that the rotations found for the 

 mixtures of the tartrate with the equivalent of two molecules 

 of the simpler inactive salts give numbers which agree with 

 Landolt's values. This is probably more than a mere coinci- 

 dence. I am at present making a somewhat closer study of it. 



The above mentioned hypothesis, while not adequate to ex- 

 plain fully the difference in behavior between the inactive salts 

 added to the tartrate, is still worthy of consideration, I think. 

 In the further progress of the work I shall test it fully. The 

 phenomenon is evidently a complex one and a study of the be- 

 havior of other double tartrates must be made before it can be 

 thoroughly understood. 



Preliminary experiments indicate that the double tartrates 

 containing thallium or antimony will well repay investigation. 

 The necessary material for such a study is now in course of 

 preparation by an assistant in my laboratory, and with this I 

 hope to be able to throw more light on the subject. 



Chicago, July 18th, 1888. 



