The Dental record . llet, who have arrived atthe same result by very different methods, the electromotive forceof a pair of bismuth and copper, when one junction is maintainedat 212° and the other at 32° Fah., is J^ of that exerted between apair of copper and zinc plates arranged in voltaic relation, as inDaniells battery. Impurity of metals may make a great differencein their thermo-electric power, and some alloys, and some of themetallic sulphides, as galena, exhibit extreme thermo-electricpower. The given by a single pair of metals is verysmall. According to Professor S. Thompson, if
The Dental record . llet, who have arrived atthe same result by very different methods, the electromotive forceof a pair of bismuth and copper, when one junction is maintainedat 212° and the other at 32° Fah., is J^ of that exerted between apair of copper and zinc plates arranged in voltaic relation, as inDaniells battery. Impurity of metals may make a great differencein their thermo-electric power, and some alloys, and some of themetallic sulphides, as galena, exhibit extreme thermo-electricpower. The given by a single pair of metals is verysmall. According to Professor S. Thompson, if the junction of acopper-iron pair be raised 1° C. above the rest of the circuit is only 137 millionths of a volt { 137 microvolts).That of the more powerful bismuth-antimony pair is for i 117 microvolts. Thermo-Electro or Thermo-Piles.—To increase the thermo-electric piles, a number of pairs of metals are joined inseries, and so arranged that the alternate junctions can be heated. 490 THE DENTAL RECORD. as shown in Fig. 64 at , whilst theother set, , are kept cool. In a bis-muth and antimony pair, the bismuth is thepositive metal but the negative pole, and theantimony is the negative metal but thepositive pole, and the current goes frombismuth to antimony across the junction. Generators of electricity have been con-structed on the above plan by Becquerel,Noe, Clamond, and others ; but owing to thedifficulty in maintaining them in effective action for any length oftime, probably owing to a permanent molecular change at thejunctions, they have not come into general use. The latest andmost efficient are those of Clamond, and M. Sudre, of Paris ;these have been used for telegraphic purposes, and also for electro-plating in the note-printing department of the Bank of Clamond pile is still employed in the workshops of ; and it has been successfully used for lighting a workshopin the Rue Saint Ambroise. The characteri
Size: 1378px × 1813px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondon, bookyear188
