Experiments on varioxis Liquids. 163 



Acids, C„ H 2n 2 . 



6. Of the series of fatty acids, the seven members corre- 

 sponding to the following values of n were examined in the 

 plate cell at ordinary temperatures: — 



8, " 6, 5, 4, 3, 2, 1. 

 The first six are purely positive, the seventh feebly but 

 purely negative ; and they fall regularly in power from the 

 first to the last. 



Caprylic acid (n=8), tried as a nonconductor, gave a faint 

 but good restoration regularly from extinction. As a con- 

 ductor, its action was much stronger ; and when the jar was 

 used, the effect of discharge at every second or third turn of 

 the plate was very brilliant. The effect from weak to strong- 

 est was purely positive, strengthened by tension parallel to 

 lines of force, and extinguished perfectly by compression. 



I never obtained this liquid, nor indeed any of the following 

 acids, in a state of perfect (optical) purity. After any amount 

 of filtering, there were always some visible specks left, solid 

 particles apparently of the acid itself, or of some chemically 

 homologous matter. 



Caproic acid (n=6) is distinctly weaker than the last, but 

 otherwise hardly distinguishable from it in experiment. As 

 a nonconductor, it gave no satisfactory effect in the polariscope. 

 Tried as a conductor, with or without the jar, it gave a fine 

 restoration, which was very brilliant with strong discharges ; 

 and the effect, weak or strong, was always purely positive, 

 strengthened by tension, and extinguished by compression. 



Valeric acid (n = b) acts as a weak photogyre, barely sepa- 

 rating the red and blue at extinction. Tried as a conductor, 

 without the jar, it gave a regular effect, which was merely 

 strong enough to be characterized as purely positive. With 

 the jar it gave a series of brilliant effects, always purely posi- 

 tive by both tests. 



"With either of these three acids, it is easy to obtain a large 

 range of optical effects, from very intense to evanescent, in 

 one experiment. The jar is well charged, say by twenty turns 

 of the plate, and the discharging balls are brought at short 

 intervals into instantaneous contact, so as to discharge the jar 

 gradually and discontinuously through the cell. Working in 

 this way with valeric acid, and with one moderate charge of 

 the jar, I have counted up to about fifty good restorations in 

 the polariscope. 



Butyric acid (n = A), tried as a conductor, but without the 

 jar, gave an effect which was too faint to be characterized, 

 showing a distinct fall of power in comparison with the last 



