30 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVIII.) 
boih metal and wood, and even the sulphur cone negative, only once did it render 
metal positive. Powdered resin generally rendered metal negative, and wood positive, 
but presented irregularities, and often gave two states in the same experiment , first 
diverging the electrometer leaves, and yet at the end leaving them uncharged. Gum 
gave unsteady and double results like the resin. Starch made wood negative. Silica , 
being either very finely powdered rock-crystal or that precipitated from fluo-silicic 
acid by water, gave very constant and powerful results, but both metal and wood 
were made strongly positive by it, and the silica when caught on a wet insulated 
board and examined was found to be negative. 
2139. These experiments with powders give rise to two or three observations. In 
the first place the high degree of friction occurring between particles carried forward 
by steam or air was well illustrated by what happened with sulphur : it was found 
driven into the dry box-wood cone opposed to it with such force that it could not be 
washed or wiped away, but had to be removed by scraping. In the next place, the 
double excitements were very remarkable. In a single experiment, the gold leaves 
would open out very wide at first, and then in an instant as suddenly fall, whilst the 
jet still continued, and remains at last either neutral or a very little positive or nega- 
tive : this was particularly the case with gum and resin. The fixation upon the wood 
of some of the particles issuing at the beginning of the blast and the condensation of 
moisture by the expanding air, are circumstances which with others present tend to 
cause these variable results. 
2140. Sulphur is nearly constant in its results, and silica very constant, yet their 
states are the reverse of those that might have been expected. Sulphur in the lump 
is rendered negative whether rubbed against wood or any of the metals which I have 
tried, and renders them positive (2141.), yet in the above experiments it almost always 
made both negative. Silica, in the form of a crystal, by friction with wood and 
metals renders them negative, but applied as above, it constantly made them strongly 
positive. There must be some natural cause for these changes, which at present can 
only be considered as imperfect results, for I have not had time to investigate the 
subject. 
2141. In illustration of the effect produced by steam and water striking against 
other bodies, I rubbed these other substances (2099.) together in pairs to ascertain 
their order, which was as follows : — 
1. Catskin or bearskin. 
2. Flannel. 
3. Ivory. 
4. Quill. 
5. Rock-crystal. 
6. Flint glass. 
7. Cotton. 
8. Linen, canvas. 
9. White silk. 
10. The hand, f Iron. 
11. Wood. Copper. 
12. Lac. Brass. 
13. Metals .... Tin. 
14. Sulphur. Silver. 
Platinum. 
