368 Mr. G. Gore. Effects of different Positive Metals [June 21, 



called to some curious roots, the secondary branches of which arc 

 given off in regular verticils ; besides these plants two other distinct 

 kinds of roots are described, in each of which the cortical parenchyma 

 is characterised by containing numerous lacunaa of the type so com- 

 mon amongst aquatic and semi-aquatic forms of vegetation — e.g., 

 Nymphcea. All the above objects are from the Lower Carboniferous 

 beds at Halifax. 



VI. " Effects of Different Positive Metals, &c., upon the Changes 

 of Potential of Voltaic Couples." By G. Gore, F.R.S. 

 Received June 13, 1888. 



The following effects upon the minimum change of potential of a 

 voltaic couple in water (' Roy. Soc. Proc.,' May 26, 1888), and upon 

 the change of potential attending variation of strength of its exciting 

 liquid (ibid., May 31, 1888), were obtained by varying the kind of 

 positive (and of negative) metal of the couple, and by employing 

 different galvanometers. The measurements were made by the 

 method of balance, with the aid of a thermo-electric pile* (' Birming- 

 ham, Phil. Soc. Proc.,' vol. 4, p. 130), and the numbers have been 

 corrected for errors caused by absorption of hydrogen by the platinum. 

 The water employed was ordinary distilled water, redistilled after 

 addition of a minute amount of sulphuric acid, and was quite free 

 from ammonia. 



Table I. — Mg + Pt + HOI in 465 grains of Water at 17° C. 



Grains. 



Volts. 



Grains. 



Volts. 



0-15 



0-13563 



0-12066 



1-7119 

 1-6946 

 1 -6804 



-0458 

 -0308 

 -0158 



1-6861 

 1 -6804 

 1 -6746 



0-10569 

 0-09072 

 -07575 

 -06078 



1-6861 



>5 



-0009 

 0-0008 

 water 



1 -5946 

 1-566 



With an ordinary astatic galvanometer of 100 ohms resistance, the 

 smallest proportion of the anhydrous acid required to change the 

 potential, lay between 1 part in 616,666 and 570,000 parts of water; 



* This instrument is manufactured by Messrs. Nalder, Brothers, Horseferrj 

 Road, Westminster. 



