1871.] 



Action of Metals and Liquids. 



335 



Experiment 3. — With 100 grains of racemic acid in 2 ounces of water 

 the hot cup was negative, value of deflection '00005. 



The negative condition excited in the hot platinum cup in the solutions 

 of citric and tartaric acid agrees with the results obtained with copper 

 in those liquids. 



Fig. 3. Fig. 4. 







A 





33 







. 













. " ■ • ' i 



Mm 









4 v ~~- 



— 1 — ' . 



I have already shown (Phil. Mag. 1857, vol. xiii. p. 1) that the currents 

 obtained with platinum electrodes are not due to the influence of atmo- 

 spheric air upon the liquid and metal at their line of mutual contact ; for, in 

 the experiments there recorded, atmospheric air was entirely excluded, and 

 the liquids were previously well boiled. 



To test the influence of size of the cold electrode, I took a platinum dish, 

 A (see fig. 4), 5 inches wide and 1 J inch deep, in a glass vessel of the 

 annexed form, B, closed at its lower end by a cork, and containing in its 

 neck two platinum electrodes, one consisting of a wire, C, and the other of 

 a sheet 2 inches long and 2 inches wide in the form of a cylinder, D. 



With a cold mixture composed of 3| ounces of water and \ of an ounce 

 by measure of strong sulphuric acid, and the sheet of platinum as the 

 lower electrode, on pouring boiling water into the dish a deflection of the 

 value of '0064 was obtained, the cold electrode being positive ; but with 

 the wire as the lower electrode no perceptible deflection occurred. These 

 results were obtained repeatedly. The electric currents are therefore 

 largely dependent upon the size of the cold electrode. 



General Results. 



The chief fact brought out conspicuously by these experiments with 

 copper dishes is, that in many cases an increase of chemical action pro- 

 duced by heat, instead of making the hot metal electro-positive, makes it 

 considerably negative. 



The results show that hot copper was positive to cold copper in the fol- 

 lowing liquids : — hydrochloric, hydrocyanic, boracic, and tribasic or ortho- 

 phosphoric acids ; chloride of copper (weak solution) ; chloride of cobalt ; 

 chloride of manganese ; chromic acid ; chloride of chromium ; sulphate of 

 zinc (weak solution;; sulphate of magnesia; chloride of calcium ; nitrate 

 and chloride of strontium ; chloride of barium ; nitrate of sodium (strong 

 solution) ; chloride, iodide, carbonate, and biborate of sodium ; sulphate 



