384 Mr. W. Coldridge on the Electrical and 



Professor J. J. Thomson, F.R.S., for the suggestion of ex- 

 amining the conductivity of the chloride at the boiling-point ; 

 and to W. N. Shaw, Esq., as well for the use of his room at 

 the Cavendish Laboratory as for the interest he has kindly 

 evinced in my results ; and, lastly, to Professor Dixon, F.R.S., 

 who has kindly read my manuscript. 



Part I. — Experimental Observations. 



Preparation of Stannic Chloride. — Stannic chloride was 

 prepared by passing a current of dry chlorine gas over melted 

 tin. The collected distillate was a yellow powerfully faming 

 liquid ; the yellow colour was due to an excess of chlorine, 

 which was removed by allowing the liquid to stand for two 

 days over granulated tin. After decantation it was distilled 

 from a fresh quantity of granulated tin. The liquid then 

 boiled at a perfectly fixed temperature of 112° 0,, which is 

 accurately the boiling-point observed by Andrews, and differs 

 considerably from Dumas's value of 120° C. The liquid thus 

 obtained is perfectly colourless : it exhibits a great attraction 

 for moisture, combining to produce a white crystalline solid, 

 SnCl 4 . 5H 2 (Lewy), insoluble in the chloride. 



Electrical Conductivity of the Pure Chloiide. — The conduc- 

 tivity of the pure stannic chloride was examined by placing 

 it in a V-tube with platinum electrodes : in the circuit were 

 included a high-resistance galvanometer (4000 ohms), and 

 twenty secondary cells of electromotive force of 40 volts. On 

 completing the circuit by depressing a key not the slightest 

 effect was observable ; the insulation was absolute within 

 these limits of delicacy, and was in marked contrast to the 

 conductivity of a pencil-streak of black-lead on paper, for, 

 with the latter in circuit instead of the former, the spot of 

 light immediately moved off the galvanometer-scale. 



In order to test whether the insulating power was appre- 

 ciably affected by elevation of temperature, the containing 

 V-tube was heated in a bath of aniline. But as the tempera- 

 ture rose to 20 c , 30°, 40°, 100°, and even to the boiling-point 

 when the stannic chloride was distilling freely — and this last 

 observation is of particular import because the physical homo- 

 geneity of the liquid agitated now with bubbles of vapour 

 has been disturbed — no conductivity could be observed. To 

 arrive at some concept of the degree of insulating power, 

 the following experiment was performed. The same galvano- 

 meter was placed in circuit with the resistance of one meo-ohm 

 and supplied with the electromotive force of one Daniell cell ; 

 the deflexion then observed was thirty-five of the scale- 

 divisions of the galvanometer. An electromotive force of 



