282 
MESSRS. THOMAS MARTIN LOWRY AND PERCY CORLETT AUSTIN 
by the addition of an excess of potash to tartar emetic (see below, p. 285). A detailed 
investigation of the aluminium tartrates from this point of view would be of great 
interest, but was not undertaken in the course of the present research.* 
Confirmation has, however, been obtained of Biot’s observation that the alkali- 
tartrates become lsevorotatory when dissolved in an excess of strong alkali; thus whilst 
the rotatory power of potassium hydrogen tartrate in dilute solutions is about twice as 
great as that of the free acid, and the rotatory power of the neutral potassium salt is 
about three times as great, the further addition of potash (perhaps producing some 
displacement of hydrogen by potassium in the two hydroxyl-groups) causes the rotatory 
power to diminish and finally to become reversed in sign. Biot found (‘ Mem. Acad. 
Sci.,’ 1838, vol. 16, p. 345, and Table 6, facing p. 338) that a solution containing 
K 2 C 4 H 4 O fi , TbO, 2'6 per cent. ; K 2 0, 36'2 per cent. ; HLO, 61‘26 per cent, 
was lsevorotatory and gave the remarkable dispersion shown by the following readings, 
red — 0'433°, yellow — 0'617°, green — 0'2°, 
where the shallow maximum is of opposite sign to that observed in tartaric acid. Our 
own observations on a similar, but more concentrated, solution containing 
KAHA, HA 2'10 gr. ; K 2 0, 36‘43 gr. ; H,0, 51 *89 gr 
in about 60 c.c. (density 1*504) gave a series of very small negative readings from which 
the molecular rotations shown in Table XIV. (a) may be deduced. The dispersion is 
obviously not simple, and the high value of the dispersion ratio a 4358 /a 5461 = 3*3 
suggests that the rotation would become positive in the infra-red. Biot’s reversed 
maximum is not confirmed by our observations. 
Sodium tartrate is more readily soluble both in water and in strong alkali. Biot 
(ibid., p. 364, and Table 8 at end of volume) found that a solution containing 
NaAHA, 2HA 13‘27 per cent. ; Na 2 0, 19'69 per cent. ; H 2 0, 67'04 per cent, 
gave the following rotations :— 
red —2 '67 5°, yellow —4°, green — 4’700°. 
Our own observations on a stronger solution containing 
NaAHA, 2HA 13-3 gr. ; Na 2 0, 20‘41 ; ELO, 59MB, 
in about 66 c.c. (density 1*4093) gave the very substantial negative readings shown in 
Table XIV ( b ). These readings are large enough to give smooth values (fig. 6) for the 
molecular rotatory power of the dissolved salt. They confirm the increase of lsevoro- 
tatory power with diminishing wave-length already recorded by Biot, but they do not 
* This investigation is now being carried out by Miss Graham (26.1.22). 
