4<;s 



ELECTRICITY. 



Datmntire 

 Klrftridty. 



of the lami- 

 na of Miu- 



ojr uk. 



Mr WUson 

 on the elec- 

 tricity of 

 wood tha- 



fragments from reaching the eye, tin- drop was bur-t 

 hy break ing off n part ct' it* tail, and the whole of 

 it appeared luminous ; go that at the iii-l.nit of the 

 fracture, a quantity of tkint light, <>f the - une -h.npe 

 and size n- the drop itself, was distinctly vi.-iblr. The 

 drop which gn\r this singular result wii- made of flint 

 glow, and was the largest lint ho had ever seen. I 

 ry other flint gla-s drop produced a distinct elivtric.il 

 light ; l>ut in none of them, except the large one, could 

 the luniinoiis -liape of the drop. The SUM 

 light appeared when they were hurst under water. 

 Tin- -mall irhi-s drop- made of bottle i;h-> never exhi- 

 bited any light at the moment of bursting : hut it was 

 almost always visible, in small sparks, in bottle glass 

 drops of n larger si/.e. 



A similar phenomenon i exhibited in Mu.-covy talc, 

 when its lamina-are suddenly torn asunder. Klcctrici- 

 t\ i- immediately developed, and a bright flash of light 

 is exhibited. 



Mr William Wilson found, that if a piece of dry and 

 warm wood is suddenly split asunder, the two conti- 

 guou> re electrified, the 01;. !y and the 



other negatively. 



When a stick of sealing wax is broken in two, the 

 two fractured extremities are distinctly electrified, the 

 one end positively, and the other negatively. 



Connected in some measure with the preceding re- 

 sults. are those which were obtained by Mr Wilson 

 ;!ng the electricity of wood shavings. Having 

 had frequent occasion to work very dry wood thai had 

 lain for several hours over a large tire, Mr Wilson 

 often observed the shavings adhering to the tools, 

 and to every thing that they touched. He therefore 

 instituted a set of experiments, for the purpose of as- 

 certaining the origin of the electricity, and obtained the 

 following general results. When dry wood was scra- 

 ped with a pii-ce of window glass, the shavings always 

 exhibited positive electricity. When the wood was 

 chipped with a knife, the electricity of the chips was 

 positive when the wood w;>s hot. and the edge of the 

 knife not very sharp, but negative when the wood was 

 perfectly cola. When the edge of the knife was very- 

 sharp, the chips were negatively electrified whatever was 

 the temperature of the wood. Having insulated a 

 penknife, by fixing it into a glass tube covered with 

 sealing wax, he found that it always possessed an electri- 

 city contrary to that of the chips, which were most fre- 

 quently positive. The surface of the wood from which 

 the chips were detached was seldom electrified, and 

 when it was, the electricity was always very weak, and 

 of the same denomination as that of the weakest of the 

 other two. See Thomson's Annals (if Pliilotopky, vol. 

 iv. p. 4-48. Nichulson'f Journal, 8vo, vol. iv. p. 4953. 



SECT. V. On thr Electricity jrrodnced by dropping 

 Ponders on a Metallic Plate. 



F.ltriciiy 



CAVALLO and Mr Bennet have shewn, from nu- 



stance was used, it was placed in some electric tub- 

 stance, such as a glass phial, or a plate of scaling wax. 



In inakni? -mil experiments, it is necessary to liave 

 the p< dry :uul warm as possible, othmsi 



signs u ity will be obscrxcd. With these pre- 



c-iuiioiis. Mr I avallo obtained the following result-. 

 1'owdired ro a in lit fall from a metal spoon, glass, or 

 paper, communicates a strong negative electricity to 

 the plate ; and when the spoon, or body which held 

 the powder, was insulated, it was strongly positive. 

 Flowers of sulphur electrified the plate negatively, but 

 not so strongly. 1'ov. d t red gla>s, dropped from a warm 

 and dry piece of paper, communicated a negative 

 tricity to the plate, but it was weaker than that of the 

 r,i-in. When it was dropped from a br.i-> cup, the 

 electricity was very weak but positive. Steel tiiint:- 

 dropped either from paper or from a glass phial, dec. 

 trified the plate negatively ; but brass filings, let fail 

 under the same circumstances, electrified it positively. 

 Gunpowder, very line emery, and the amalgam of tin- 

 toil and mercury, when dropped from a glass phial, 

 electrified the plate negatively : whcrea- mercury itself. 

 let fall from a gloss phial, electrified the plate positive- 

 ly. Soot, and the ashes of piteoid mixed with small 

 cinders, when dropped from n piece of paper, electri- 

 fied the plate negatively. 



Mr Mennet found, that powdered chalk falling from 

 one plate to another placed upon his electron 

 trifled it negatively ; and the same effect was produced 

 by red ochre, yellow rosin, coal ashes, powdered cro- 

 cus metallorum, aiirum mosaic.um, black lead, powder- 

 ed quicklime, amber, lapis cahuiiinaris, Spanish brown, 

 powdered .sulphur, flowers of sulphur, iron filing-. 

 of iron, and sand. 



The most accurate experiments, however, which have 

 been made upon this subject, \ve owe to Mr Si: 

 who employed two methods of bringing the ! 

 into contact: 1st, By sifting the powders on the cap of 

 a delicate electrometer through a fine sieve, whi.-h was 

 completely cleaned after every experiment; :ind. '_'d!y, 

 By bringing an insulated copper plate repeatedly in 

 contact with the powders, spread out into an extensive 

 surface on a dry sheet of paper. By the first of these 

 methods he obtained the following results. 



Nfgitliiif electric!! '/ was produced by the following 

 bodies, when sifted oil the cap of an electrometer. 



niii '. 



Rennet's 

 experi- 

 ments. 



l\]KTI- 



mcntt. 



. 



ofpowdcn merous exjjcriments, that when electrics or conductors 

 ih* fall on are reduced to powder, the powders may be rendered 

 nwullic electrical, merely by dropping them on an insulated 

 ' tatc- plate. 



Mr Cavallo insulated a metallic plate upon a glass 

 stand, and connected it with a cork ball electrometer. 

 He held the powder to be tried in a spoon, about six 

 inches above the plate, r.nd allowed it to fall gradually. 

 The electricity acquired by the powder was thus com- 

 municated to the plate, and thence conveyed to the 

 electrometer. When the powder of a conducting sub- 



Copper, 



Iron, 



Zinc, 



Tin, 



Bismuth, 



Antimony, 



Nickel, 



Black lead, 



Lime, 



Magnesia, 



Barytes, 



Strontium, 



Alumine, 



Silex, 



Brown oxide of copper, 



White oxide ofar-ciiic, 



Hed oxide of lead, 



Litharge, 



White lead, 



Red oxide of iron, 



Acetate of copper, 



Sulpliate of copper, 



Sulphate of soda, 

 I'liospliate of soda, 

 Carbonate, of soda, 



innate of ammonia. 

 Carbonate of potash, 

 Carbonate of lime, 

 Muriate of ammonia. 

 Common pearl ashes, 

 Boracic acid, 

 Benzoie acid, 

 Oxalic acid, 

 Citric acid, 

 Tartaric add. 

 Cream of tartar, 

 Oxymtiriate of potash, 

 Pure potash, 

 Pure soda, 

 Rosin, 

 Sulphur, 

 Sulphuret of lime, 



ch, 

 OrpiiHcnt. 



