352 J. M. Long — Polarization of Tartrate Solutions. 



acids and several neutral salts. Under still other circumstances 

 the rotation of an active body can be very greatly increased by 

 the addition of certain inactive ones, as is well illustrated by 

 G-ernez {Berichte der Deutschen Chem. Gesell., xx, Kef. 251), 

 in his experiments on mixtures of tartrates with molybdates, 

 arsenates, tungstates, etc. He found, for instance, that the ad- 

 dition of NH 4 Mo0 4 to a solution of tartaric acid increased its 

 rotation about fifty times. 



This subject is one of great practical interest as well as of 

 scientific importance, and it seemed to me that further investi- 

 gation on the rotation of the tartrates must yield results of 

 some value. 



The following pages discuss results obtained with solutions 

 of Rochelle salt in an investigation begun above a year ago and 

 which is still in progress.* 



Apparatus and methods. 



In my experiments I employed a new model Laurent instru- 

 ment made by Schmidt & Haensch, and used with this polari- 

 zation tubes 200 and 220 mm in length, surrounded by a water 

 jacket. The tubes were carefully measured and were found to 

 differ so slightly from the given length (less than -05 mm ), that I 

 employ the whole numbers instead of introducing a fraction in 

 the calculations. Bj means of suitable appliances the temper- 

 ature of the solutions under examination was kept within 0°*2 

 of 20°, as shown by a delicate thermometer. In most cases, 

 however, this extreme accuracy in the control of the tempera- 

 ture was not necessary as the variations caused by change of 

 temperature were very small. In each test a dozen or more 

 readings were made for each position of the analyzing Nicol, and 

 on the two verniers 180° apart. The instrumental error was 

 almost inappreciable to begin with, and disappeared entirely 

 by taking a mean of all the readings. 



At a temperature of 20° a solution of tartaric acid containing 

 15 gm in 100 cc showed a specific rotation [a] D = 13°-03. This is 

 diminished when the solution contains free mineral acids, and is 

 also much diminished when certain neutral salts are added. 

 With a solution containing 15 gm of tartaric acid and 8 gm of 

 sodium chloride I found the specific rotation less than one-half 

 as much as before, viz : [a] D = 6° "16. 



If instead of starting with tartaric acid a neutral tartrate be 

 taken and various salts added quite different results are ob- 

 tained. In the first place, the change in the specific rotation is 

 much less than when the acid is used, and besides this the na- 



* This investigation was begun before the work of Gernez came to my notice, 

 and before the publication of recent papers by Landolt (Berichte, 1888, p. 191), in 

 which reference is made to the behavior of certain tartrates. A second paper will 

 deal with other tartrate solutions. 



