and the lower plate was at the atmospheric temperature, varying from 55° to 65° F. In all instances where the temperature is not specified, the upper plate was at 210° F. Distilled water was used in making all the various solutions, unless otherwise stated.

Experiment No. 1. 14 oz. by measure of water and 1 oz. of a saturated solution of pure sodic carbonate. Platinum plates. Galvanometer of 25 ohms resistance. Current Į, hot plate positive, deflection 25°. No. 2. 7 oz. of water and 7 oz. of the same saturated solution. Platinum plates. Current 7.5.

No. 3. 1 oz. of water and 14 oz. of the same saturated solution. Platinum plates. Current | 10.

No. 4. Same mixture as in No. 3. Platinum plates. Galvanometer of 100 ohms resistance.* Current | 15. (Compare Nos. 39 and 118.) No. 5. The same mixture. Silver plates. Current | 15.75.

Remarks. No sign of corrosion of the plates appeared in either of these five experiments. The current increased in magnitude with the strength of the solution.

No. 6. The same mixture. Copper plates. Current | 65.5. The upper plate was found corroded after this experiment. (Compare No. 164.)

No. 7. Upwards of forty different experiments were made with pure dilute sulphuric acid of seven different degrees of strength, varying from 12 oz. of water and 3 oz. of the acid to 14 oz. of water, and

oz. of the acid; and all the mixtures were tried with plates of platinum, gold, and palladium. The current was upward in every case, and the amount of deflection varied from 14° to 45°. (Compare Nos. 115, 116, and 117.) The currents were reverse in direction to those which would have been produced by chemical action; and were strongest with that metal which was the least likely to be chemically affected, viz., platinum.

No. 8. 14 oz. of water and oz. of sulphuric acid. Silver plates. Current 20.5.

No. 9. 14 oz. of water, and oz. of sulphuric acid. Silver plates. Current ↑ 32.

No. 10. 14 oz. of water and 3 oz. of glacial acetic acid, or 14 oz. of water, and either oz. or oz. of the acid; each mixture being used with palladium plates gave very feeble current ; and then, on suddenly applying much cold water to the hot plate, a less feeble ↑ current was produced. Platinum and gold plates gave similar effects with a mixture of 14 oz. of water and oz. of the acid.

No. 11. 14 oz. of water and oz. of thick syrupy solution of ordinary phosphoric acid. Platinum, gold, and palladium plates. Current about 5. Cold water then applied produced in each case a feeble current.

This galvanometer was used in all the subsequent experiments.

No. 12. 14 oz. of water and oz. of pure nitric acid. Platinum Palladium plates. Current ↑ 23. Gold plates. Current 12.5.

plates. Current ↑ 75. Cold water produced a feeble current J.

No. 13. 14 oz. of water and 1 oz. of pure hydrochloric acid. Platinum plates. Current ↑ 2. Gold plates. Current↑ 2. Palladium plates. Current ↑ 2. Cold water produced feeble currents. (Compare No. 143.)

No. 14. 12 oz. of water and 3 oz. of a saturated solution of pure boracic acid. Platinum plates. Current | 1.5. Cold water produced a weak current ↑.

No. 15. 12 oz. of water and 4 oz. of crystals of sulphate of copper. Plates of platinum, gold, or palladium, gave currents, strong with the two first-named metals and feeble with the last ones. (Compare Nos. 42, 43, 44, and 113.)

No. 16. 12 oz. of water, 4 oz. of crystallized chloride of copper, and oz. of pure concentrated hydrochloric acid. Gold plates. Current ↑ 52 at 160° F. and 48 at 210° F. Cold water produced a very strong current.

No. 17. The same mixture, with platinum plates. Current ↑ 54 at 170° F. and 51 at 210° F. (Compare No. 125.) Cold water strongly reversed the current.

No. 18. The same mixture, with palladium plates. Current | 45 at 190° F., and 36 at 210° F. Cold water produced a very strong current, and the upper plate was found corroded after the experiment. Remarks. These circumstances show that the downward current was due to the chemical action excited by the higher temperature. This experiment also illustrates the utility of subsequently applying cold water to reveal the true effect of heat in cases where chemical action interferes. (Compare Nos. 32, 60, and 125.)

No. 19. 7 oz. of water and 6 oz. of a saturated solution of chlorate of copper containing very little free acid. The mixture reddened blue litmus paper. Platinum plates. Current ↑ 28 at 195° F., and 15 at 210° F. Cold water produced a current. (Compare No. 126.) Gold plates. Current 54. Cold

No. 20. The same mixture. water produced a current.

No. 21. The same mixture. Palladium plates. Current ↑ 35. Cold water reduced the deflection to 0.

No. 22. A nearly saturated solution of nitrate of copper, not containing any free acid. Platinum plates. Current 8 Cold water reversed the direction of the current.

No. 23. The same solution. Gold plates. Cold water produced a current.

Current 2 at 180° F.

No. 24. The same solution. Palladium plates. Current | 15. Cold water produced a current.

No. 25. 14 oz. of a nearly saturated solution of cupric nitrate and

2 oz. of pure concentrated nitric acid. Platinum plates. Current 48. Cold water produced a strong current. (Compare No. 138). Gold plates. Current ↑ 53. Cold

No. 26. The same mixture. water reversed the current strongly. No. 27. The same mixture. Palladium plates. Current ↑ 56. Cold water produced a very strong current. The upper plate was found corroded after the experiment. Remarks. A comparison of the results of Experiments Nos. 25, 26, and 27, with those of the three immediately preceding ones, shows the effect of the free acid in increasing the negative condition of the hot plate.

No. 28. 14 oz. of water and 2 oz. of pure concentrated nitric acid. Platinum plates. Current † 20 at 160° F., and 16 at 210° F. Cold water reversed the current strongly. (Compare No. 119.)

No. 29. The same mixture. Gold plates. Current 241. Remarks. A comparison of the last eight experiments shows that a mixture of an aqueous solution of cupric nitrate with one of nitric acid yields stronger currents than either solution alone.

No. 30. A strong aqueous solution of chloride of chromium. Gold plates. Current | 44 at 200° F., and 42 at 210° F. This liquid had not been pre-boiled, and therefore many air-bubbles accumulated against the hot plate, but appeared to only slightly decrease the amount of deflection. Cold water produced a very strong current.

No. 31. The same solution. Platinum plates. Current ↑ 45 at 180° F., and 42 at 210° F. Cold water produced a very strong current. (Compare No. 123.)

No. 32. The same solution. Palladium plates. Current | 63. Cold water diminished the amount of deflection. Both the plates were a little corroded after the experiment, and each equally so. Repetition of this experiment yielded similar effects. (Compare Nos. 18 and 60.)

No. 33. 14 oz. of water and 1 oz. of acid chromate of potassium. Platinum plates. Current | 1. Cold water reversed the current. No. 34. The same mixture. Gold plates. Current 4 at 200° F.

Cold water produced a feeble ↑ current.

No. 35. The same mixture. Palladium plates. Current ↓ 5. Cold water produced a feeble ↑ current.

No. 36. The same mixture, with 1 oz. of dry crystals of chromic acid added. Platinum plates. Current↑ 44. Cold water first slightly increased and then, to a large extent, decreased the current. (Compare No. 124.)

No. 37. The same mixture as in No. 36. Gold plates. Current ↑ 14. Cold water feebly reversed the current.

No. 38. The same mixture as in No. 37. Palladium plates. Current 3 at 120° F., and † 20 at 210° F., and gradually increased to 30 by continuance of heat. Cold water first slightly increased and then

VOL. XXVII.

2 M

equally decreased the current. No signs of chemical action were observed.

No. 39. 1 oz. of water and 14 oz. of a saturated solution of sodic carbonate. Platinum plates. Current | 12, and gradually increased to 25 by continuance of heat. Cold water reversed the current. (Compare Nos. 4 and 18.)]

No. 40. The same mixture. Gold plates. Current | 28, and remained at 28 by continuance of heat. Cold water strongly reversed the current.

No. 41. The same mixture. Palladium plates. Current | 35, and gradually increased to 40 by continuance of heat. Remarks. The increase of current by continuance of heat in these three last experiments is not wholly due to an action of the liquid upon the washers. (Compare Nos. 112, 121, 142, 145, 149, 151, and 153.)

oz.

No. 42. 12 oz. of water, 4 oz. of crystals of cupric sulphate, and of pure concentrated sulphuric acid. Gold plates. Current ↑ 48. Cold water decreased the deflection to 30.

No. 43. The same mixture. Platinum plates. Current 50. Cold water diminished the deflection to 30. (Compare No. 127.) No. 44. The same mixture. Palladium plates. Current 37. Cold water sent the needles back strongly. (Compare No. 15.)

No. 45. 2 oz. of water and 12 oz. of a saturated solution of sulphate of potassium. Solution very faintly blued neutral litmus paper. Platinum plates. Current 12. Cold water produced a feeble upward current.

No. 46. The same mixture. Gold plates. No current. Palladium plates. Current | 21.

No. 47. 3 oz. of water and 12 oz. of a saturated solution of acid sulphate of potassium. Liquid strongly acid to litmus paper. Palladium plates. Current Cold water produced a very feeble | current.

No. 48. The same mixture. Gold plates. No current. Platinum plates. No current, but cold water produced a feeble downward current in cach case. Remarks. The acid sulphate behaved very much like the neutral sulphate in these and other experiments, and both behaved like the corresponding chromates. (Compare No. 128.)

No. 49. 14 oz. of water and oz. of crystals of cupric acetate. Gold plates. No current. Cold water produced a feeble | current.

No. 50. The same mixture, with platinum plates. Current Palladium plates. No current. Cold water produced a feeble ↓ current, in each case.

No. 51. The same mixture, with 3 oz. of glacial acetic acid added to it. Palladium plates; no current. Gold plates; current | 14. Platinum plates; current ↑ 14. Coid water produced a downward current in all three cases. (Compare No. 122.)

No. 52. 12 oz. of water and 4 oz. of yellow chromate of potassium.

The solution was alkaline to litmus paper. Platinum plates. Current 4. Cold water produced an ↑ current.

No. 53. The same mixture. Gold plates. Current | 1. Cold water reversed the deflection.

No. 54. The same mixture. Palladium plates. Current 23. Cold water produced an ↑ current.

No. 55. 14 oz. of water and 4 oz. of dry crystals of sulphate of nickel. The solution was faintly acid to litmus paper. Palladium plates; no current. Gold plates; current 1. Platinum plates; current 2. Probably the washers interfered.

In all three instances cold water produced feeble ↑ currents. (Compare Nos. 15, 113, and 155.)

No. 56. A strong solution of chloride of chromium in alcohol. The solution was acid to litmus paper. Platinum plates. Current ↑ 10 at 180° F., at which temperature large bubbles of vapour were formed. Cold water produced a strong current. Remarks. Probable interference produced by upper washer. (Compare No. 129.)

No. 57. 12 oz. of water and 4 oz. of crystals of nitrate of cobalt. The solution was strongly acid to blue litmus paper. Platinum plates. No current. Cold water produced a feeble | current.

No. 58. 12 oz. of water and 4 oz. of dry chloride of cobalt. The solution strongly reddened blue litmus paper. Platinum plates. Current 37. Cold water produced a very strong current. (Compare No. 120.)

No. 59. The same mixture. Gold plates. Current ↑ 38. Cold water produced a very strong | current.

No. 60. The same mixture. Palladium plates. Current ↑ 25 at 160° F., 0 at 180° F., and 11 at 200° F. Cold water produced a rather strong downward current and then an upward one. (For similar effects compare Nos. 18 and 32.)

No. 61. 12 oz. of water and 4 oz. of crystals of sulphate of glucinum.* Solution strongly acid to litmus paper. Platinum plates. Current ↑ 14 at 180° F., and at 210° F. Cold water reversed the deflection. No. 62. The same mixture. Gold plates. Current ↑3. Palladium plates. No current. Cold water produced a feeble downward cur

rent in each instance.

No. 63. 12 oz. of water and 4 oz. of chloride of ammonium. The solution was very faintly acid to litmus paper. Platinum plates. Current 14, and, in a second experiment, 1 2. Cold water reversed the deflection in both cases.

No. 64. The same mixture. Palladium plates. No current. Cold water produced a feeble | current.

No. 65. 12 oz. of water and 3 oz. of chloride of potassium. Solu

* Prepared for me by Dr. H. Trommsdorff, of Erfurt.