APPARATUS 81 



is based on the fact that when an electric current passes through 

 an imperfect conductor more or less of the energy of the current 

 appears as heat. An illustration of this is seen daily in the 

 ordinary incandescent electric lamp, in which a thread of carbon 

 or of an imperfect metal like tungsten is raised to such a tem- 

 perature that a brilliant light results. The principle is applied 

 in the heaters which for some purposes are used in the laboratory. 

 The current in this apparatus is turned into a box containing 

 carbonaceous material, the resistance of which can be diminished 

 or increased by altering its state of compression, and the tem- 

 perature resulting can be thus regulated. Apparatus of this 

 kind has several advantages for laboratory purposes ; it pro- 

 vides a steady source of heat, spread over a larger surface than 

 a flame, which may be increased at will from a gentle warmth 

 to a low red if required, it is unaffected by draughts of air, and 

 it is unattended by risk of fire when inflammable liquids, such as 

 ether or alcohol, are to be heated. An example of the use of 

 electric heaters is shown (Fig. 32, p. 62) in the distillation of wine, 

 spirits, or beer, for the determination of their alcoholic strength. 

 A measured quantity of the liquid to be tested is placed in the 

 flask, distillation is continued till all the alcohol has passed over and 

 a determinate quantity of liquid is collected. The specific gravity 

 of this liquid, compared with the figures in an alcoholometric 

 table, supplies the percentage of alcohol in the original liquid. 



Another application to laboratory purposes is shown again 

 (Fig. 34, p. 64) in the apparatus for steel analysis. The carbon 

 left after dissolution of a weighed quantity of the metal in an 

 appropriate solvent is burnt in a stream of oxygen in a tube 

 heated by the current to redness. The resulting carbon dioxide 

 is collected in weighed tubes containing caustic potash, as shown 

 in the figure, and from the increase of weight the carbon in the 

 sample can be calculated. 



The use of the electric arc for the attainments of high tem- 

 peratures is the result chiefly of the researches of the late 

 Professor Henri Moissan, 1 whose untimely death in February, 

 1907, deprived the world of a very brilliant and indefatigable 

 worker in science. One form of Moissan's furnace is shown in 



1 Moissan's career is both interesting and instructive. He was born in Paris 

 28th September, 1852, the son of an employe of the Eastern Railway Company, 

 his mother assisting the slender resources of the family by working as a dress- 

 maker, At the age of twelve he entered the municipal school at Meaux, where 

 he remained till 1870. He then obtained a situation in a pharmacy, which he 

 retained during two years, and then passed into Professor Deherain's laboratory 

 in the Museum of Natural History. Here he experienced the attractions of 



