406 



REPOKT 1886. 



Nta Size 



Determination of the resistance of a jelly-Jilled tube. 



July 1. — One of the 40 centimetre tubes filled witli plain gelatine gave 67,720 

 ohms resistance. The same tube had the jelly melted out, the tube cleared and 

 filled with dilute acetic acid (centigramme molecule in 5cc.), and its resistance 

 was now 160,000. 



Another determination, by Mance's method, ga\'e for the acetic acid filled tube 

 142,000 ohms, at 21° C. ; for 'the jelly-filled tube at 19-5, 78,000 ohms ; and for the 

 same tube filled with dilute sulphuric acid (H^SO^ in 10 cc.) 730 ohms. 



This jelly tube was then left to stand all night with its feet in dilute acetic acid. 

 By the morning its resistance had increased, as the acid soaked up into it, to 

 84,000 ohms. 



Improved experiments on the velocity of ions in free liquid. 



Any siphon tube arrangement joining two open vessels cannot be free from 

 difficulties caused by electric endosmose, whatever precautions be adopted. Hence 



a series of experiments were plan- 

 FiG. 10. ued with one of the vessels closed 



and completely full, so that no 

 more or less could be driven into 

 or out of it, either by the action of 

 the current or by changes of level, 

 except such calculable changes as 

 result from alteration of volume 

 of electrode or solution near it, or 

 from changes of temperature. Ta 

 this end the cathode vessel was 

 made of the shape shown in figure 

 10, and the experimental tube 

 fitted to it by a ground joint. It 

 was necessary to avoid evolution 

 of gas, so the cathode vessel was filled with saturated sulphate of copper solution, 

 and It was immersed in a constant-temperature water-bath. The tube was 40'7 

 centimetres long, and was filled with dilute HCl (1 centigradime molecule in 6 cc). 

 The anode vessel contained a solution of baric chloride (10 grammes salt to 100 of 

 water) and a carbon electrode. The internal diameter of the tube was -393 ceutim. 

 August 7.— The cathode vessel having been in the bath all niglit, and the tem- 

 perature bemg 16-2°, the tube was put in at x. hrs. 20 min., and the current started 

 at X. hrs. 48 mm. with a difference of potential of 51-3 volts between the electi-odes. 

 A silver voltameter was included in the circuit. 



By xxii. o'clock there was no ring formed in the tube, but in the bend near 

 the cathode end of the tube there was a slight deposit. The temperature of the 

 bath was still 16-2°. It was afterwards found that the silver plate of the voltameter 

 had dissolved, and thereby broken contact. 



August 9.— Another ^precisely similar experiment; except that a galvanometer 



J-— ^--j-'- >- ■ Current started at xii. hrs. 15 min. with E.M.F. 



50'6 volts. The galvano- 



was used instead of a voltameter. 



Fig. 11. 



meter readings fell gradu- 

 ally from 6-7° to 3-8°. At 

 x?i. hrs. 40 min. a disc of 

 precipitate was found in the 

 tube, the volts being now 

 ,. .,_ ^ , 497. The thickness of the 



disc was -17, and the positions of its two faces were 379 and 3-96 centuns. from, 

 the cathode end of the tube. Result sketched here, fig. 11. 



Summary of the experiment. 



Time taken for ring to first form, estimated at 4 hours. 

 Distance travelled by Ba, 369 centims. =b + x. 

 ). „ SO^, 3-96 centims. =a— x. 



