ELECTRICITY. 



46? 



Df scriptive Snussare was greatty surprised at observing two such 

 Electricity, inflammable fluids as 'alcohol and ether following the 

 ~~"" > ~~"' same laws in their evaporation as water. The evapo- 

 Experi- ration was always greater at the time of the strongest 

 mmts of heat, t | lan w hen the heat was weakest. It then dimi- 

 " re ' nished to a certain point, and afterwards augmented till 

 the heat was feeblest. In the ether too, the combustion 

 had no sensible influence on the rapidity of the evapo- 

 ration. 



Saussure now wished to observe the phenomena of 

 evaporation in a crucible almost wholly shut. He there- 

 fore took a granade S inches in diameter, and brought 

 to a white heat, and injected into it distilled water. A 

 jet of brilliant flame was emitted from the mouth of the 

 granade. A similar effect was produced at the follow- 

 ing projections, till the heated granade had the colour 

 of a cherry; but the brilliancy and heat of the flame 

 diminished gradually with the heat. Saussure suppo- 

 ses that the flame arose from the inflammable air, produ- 

 ced by tlie decomposition of the water, or by that of the 

 iron. Whenever there was any flame, there was no ap- 

 pearance of electricity ; but as soon as the flame ceased, 

 the electricity appeared. The electricity was always 

 positive at the first experiment, but in the second it ap- 

 peared at first negative, and then nothing, when the small 

 measure of water was projected into the granade ; but 

 when half an ounce of water was thrown into it, the 

 electricity was positive. 



In order to explain the preceding experiments, M. 

 Saussure supposes that the electricity is positive with 

 those bodies that are c.ipablc of decomposing water, or 

 of being themselves decomposed by their contact with 

 the water, and that it is negative with those which are 

 not decomposed or altered. This supposition was sug- 

 gested by the fact that china and silver always produ- 

 ced negative electricity, while iron and copper gave po- 

 sitive electricity. If substances capable of being oxi- 

 dated, had constantly given a positive electricity, while 

 those which do not oxidate had given a negativf elec- 

 tricity, the preceding supposition would have acquired 

 a great degree of probability ; but the phenomena have 

 not always followed this law, a negative electricity 

 being sometimes produced by the iron and the copper, 

 and a positive electricity by the silver. Saussure re- 

 marks, that he was not much embarrassed by the first 

 of these facts, for the iron and the copper are oxidated 

 with great facility in a brisk fire, and become covered 

 with a scaly crust, which, with the same degree of heat. 

 is not susceptible of farther alteration. If this crust 

 should therefore cover the bottom of the crucible, the 

 drop of water will no longer be in contact with an oxi- 

 dable substance, and therefore no farther decomposi- 

 tion will take place, and consequently no farther gene- 

 ration of electricity. A part of the natural electricity, 

 however, of the apparatus, will be absorbed by the \ "i- 

 pours which are still formed, and therefore the appara- 

 tus will be electrified negatively. If, by any accident, 

 some of the scales should be so far de'tached that the 

 fluid will touch some parts of the metal, it ma^ Imp- 

 pen that the quantity of electriiky thus generated com- 

 pensates exactly for that which the vapours absorb, and 

 consequently the electricity will be nothing. If the 

 scales are still more detached, the electricity will be su- 

 perabundant ,and consequently positive. For the ^.im 

 reaon a larger quantity of wa'er giws constants 

 sitive electricity, when it is poured into an iron or cop- 

 per crucible, because it attacks the metal in a greater 

 number of part.", and finds more easily the pjiru 

 sible to its action. Hence, also, a strong positive elec- 



tricity is produced when a mass of red hot iron is 

 thrown into water, for the points of contact being more 

 numerous, a more abundant decomposition takes place. 



Saussure found it more difficult to explain why silver Experi- 

 sometimes gives a positive electricity. He conjectured, [f 

 however, that it arose from foreign bodies, such as cop- 

 per or other oxidable metals being mixed with the silver. 

 This conjecture originated in his observing, that though 

 the crucible was extremely clean, and the distilled wa- 

 ter very pure, yet when the water was reduced to a 

 drop, by evaporation, the drop always appeared black- 

 est, and left a brown or black globule after the evapo- 

 ration was completed. 



In order to verify this explanation, he boiled spi- 

 rit of salt in his silver crucible, and after having 

 washed it with much care, he found that the electricity 

 which it produced was always negative, even when he 

 projected half an ounce of water into the crucible. 



He also observed, that when quartz, brought to a 

 white heat, was plunged in water, positive electricity 

 was produced ; a result which he ascribes to a small 

 quantity of iron which may have existed in the quartz. 



The production of negative electricity by burning 

 charcoal greatly perplexed our author. In his firt ex- 

 periments he found the electricity to be positive, b'it 

 observing that Volta had found it to be negative, 1 c 

 discovered the cause of his mistake, and afterwards 

 obtained the same results as those of Volta. He sup- 

 poses that it may arise from the readiness with w hicli 

 that substance loses its heat in contact with water. 



Saussure endeavoured to obtain electricity from com- 

 bustion, but his attempts were fruitless, although Volta 

 had obtained distinct indications of it in similar cases. 

 He burned different bodies upon an insulated chafing 

 dish, sometimes with a clear, and sometimes with a 

 smoking flame ; and he endeavoured suddenly to ex- 

 pletle small heaps of gunpowder, but no electricity 

 whatever appeared. 



His attempts to procure electricity without ebulli- 

 tion were equally fruitless. He exposed great surface . 

 such as six square feet of wet linen, before a large fire, 

 and insulated it by silk cords. When the linen w; s 

 strongly heated, a greater quantity of vapour was pro- 

 duced than in a coffee-pot boiling on a chafing-dish, 

 and though he used the most delicate electrometer, yet 

 no electricity could be seen. He likewise spread out 

 on the moist ground a large plate of white iron, and 

 heated it strongly on a chafing-dish, but though thj 

 earth exhaled a great quantity of vapour, no elec- 

 tricity was produced. See La Place and Lavoisier, 

 Mem. Acad. Par. 1781, p. 292 ; Volta, Journal de Phi,- 

 sitine, 1783; and Saussure, Voyages dans Ics Al-pes, 8vo, 

 edit. 178(1, torn. iii. p. 316 347. 



SECT. IV. On Electricity produced by a srpacajiom of 

 1'uits. 



OWE uf the most singular electrical phenomena which 1 tii^;.:- 

 belongs to t'ie piv>cnt .Section, in the evolution of dec- '''" fr " m 

 trie light by the bursting of the unannealed glass, tears, J*^*" 8 * 8 

 called Prince liupert's drops ; a fact which was disco- ncB i c d a]^. 

 vered by Dr Brewster. These drops, which he found drops. 

 t" | '.'.--.ess the property of trail-polarising light, were 

 regularly crystallised, and had three different clcages: 

 one like that of a melon, diverging from the apex of the 

 drop; another concentric with the surface of the. drop: 

 afid a third oblique to the axis. Having laid one of 

 these drops upon a table in a dark room, and co\ered 

 it with a plate of thick gUiss, to prevent any of the 



