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MESSRS. THOMAS MARTIN LOWRY AND PERCY CORLETT AUSTIN 
negative term must therefore be weighted somewhat heavily to produce any marked 
alteration in the form of the curve. 
8. Negative Rotations in Solutions of c/-Tartaric Acid and its Salts. 
Although the common form of tartaric acid, and the tartrates derived from it, are 
usually dextrorotatory, negative rotations are occasionally observed, especially at high 
concentrations and low temperatures, and in the more refrangible portions of the spectrum. 
Biot, who had predicted this phenomenon in 1838 ( £ Mem. Acad. Sci.,’ 1838, vol. 16, 
p. 269), detected it twelve years later in the cold, glassy acid ( £ Ann. Chim. Phys.,’ 1850, 
vol. 28, p. 353) ; the more elaborate work of Bruhat (‘ Trans. Faraday Soc.,’ 1914, vol. 
10, p. 89) on the rotatory power of the anhydrous acid has shown that, whilst the 
rotations are positive in the red and yellow regions of the spectrum, they become nega¬ 
tive for wave-lengths less than 5600 at 15° C. None of the aqueous or alcoholic solutions 
examined by Biot gave negative rotations, but Lepeschkin (‘ Ber. Deutsch. Chem. 
Gesell.,’ vol. 32, p. 1180-1184) detected a negative rotation [a] 4 2 4 ° 8 0 2 = —1-22° in 
the dark blue region of the spectrum when working with a supersaturated aqueous 
solution containing 66-5 per cent, by weight of tartaric acid. Our own observations 
include negative readings in the violet region for unsaturated solutions containing 50 
grams of tartaric acid in 100 c.c. of solution; and Nutting (‘ Physical Review,’ 
vol. 17, p. 11) has observed very large negative rotations, up to [a] 2 7 9 5ol9 0 = — 296*8°, 
in the ultra-violet, in a solution containing 28*62 grams per cent, of tartaric acid. 
Grossmann ( £ Trans. Faraday Soc.,’ 1914, vol. 10, p. 63) observed only positive 
rotations in methyl alcohol, but negative values have been recorded by Arndtsen 
(' Ann. Chim. Phys.,’ 1858, vol. 54, p. 415) for more concentrated solutions. 
Grossmann showed, however, that solutions in ethyl alcohol, even at a concentration 
as low as 5 per cent., give negative rotations in the blue region beyond 4700, whilst 
similar solutions in propyl alcohol are lagvorotatory beyond 5200. Negative rotations 
for sodium light have been observed in solutions of tartaric acid in acetone mixed 
with ether or with chloroform (Landolt, ‘ Ber.,’ 1880, vol. 13, p. 2333), in water 
mixed with butyl alcohol (Pribram, £ Monatshefte,’ 1888, vol. 9, p. 485) and in 
alcohol mixed with benzene, toluene, chlorobenzene or ethyl bromide (Pribram, 
£ Ber.,’ 1889, vol. 22, pp. 6-11). 
This depression of rotatory power and ultimate reversal of sign may be regarded as 
a result of getting the tartaric acid into solution in much the same condition as that in 
which it exists in the anhydrous amorphous state, without developing the great increase 
of dextrorotatory power which results from hydration, or the lesser increase which results 
from interaction with the lowest members of the series of alcohols. A similar depression 
of dextrorotatory power is produced by formic acid, acetic acid, and especially propionic 
acid (Grossmann, loc. cit., p. 65) as well as by mineral acids. In the special case of 
sulphuric acid, Biot found that the addition of 20 per cent, of the strong acid to an 
aqueous solution of tartaric acid lowered its specific rotatory power by about one-third 
