16 Mr. C. V. Boys on Quartz as an Insulator. 



in distilled water, a process which Warburg and Ihmori* have 

 shown is necessary in order to make the glass insulate as well as 

 possible. There is no appreciable difference between the rate at 

 which positive and negative electricity escapes from the leaves. 



The quartz insulator was then treated in various ways to 

 see how well it is likely to retain its insulating power. It 

 was boiled for five minutes in a weak solution of potash and 

 washed. It was boiled for the same time in a strong solution 

 of potash and washed. In both cases it insulated as before. 

 It was dipped for two minutes in melted potash and washed. 

 In moist air it insulated better than either soda or lead-glass, 

 but not so well as before treatment with potash. Boiling in 

 strong hydrochloric acid did not restore the lost power. A 

 new hook was not affected by boiling in strong hydrochloric 

 acid, or by heating in a batswing gas-flame. 



Perhaps the most surprising result is obtained by dipping 

 the quartz hook in water or ammonia, and immediately hang- 

 ing on the leaves while the water is standing upon the hook 

 in beads. Even so no difference is observed in its insulating- 

 power. If it is dipped in a solution of potash this is not the 

 case ; but of course the insulation is restored by washing. 



The perfect equality of the rate at which the charge escapes 

 when the leaves are suspended from lead-glass in dry air, or 

 quartz in dry or moist air, makes it probable that this loss 

 of charge is not due to leakage along the insulator, for it is 

 very unlikely that, under these different circumstances, the 

 loss should be exactly alike. It is more probable that the loss 

 is due mainly to convection through the air. This is made 

 certain by the following considerations. The same leaves, 

 when hung by the same hook in another box which was badly 

 made and rough inside, lost their charge much more quickly, 

 but, as before, at the same rate in the three cases. On the 

 other hand the leaves, when suspended in the best instrument 

 by a quartz fibre about ten times as long and one hundredth 

 of the diameter of the piece B (that is, by one which would 

 insulate a thousand times as well if the loss was due to surface 

 creeping, or a hundred thousand times as well if it were due 

 to actual conduction) , lost their charge practically at the same 

 rate as before. 



Pieces of polished rock-crystal, such as are used as objects 

 for the polariscope, also insulate well ; but they do not seem 

 to be quite so free from the influence of moisture as the fused 

 quartz. The same is true with regard to the natural faces 

 and the fractured surface of the crystal. 



The electromotive forces required to produce different diver- 

 * Wied. Ann. xxvii. p. 481 (1886). 



