8 M. H. Herwig on the Disintegration of the 



of particles subjected to the action of disintegration, perhaps as 

 signified by Grove's experiment. Only it would be desirable to 

 approach this question less indirectly and under the necessity of 

 observing fewer conditions. 



In the first place, it seems requisite to produce the luminous 

 arc in a medium not chemically proportioned, between two che- 

 mically different electrodes, and by weighing and quantitative 

 analysis of the electrodes to be clear about the amount of disin- 

 tegration. The loss of weight of an electrode during an experi- 

 ment, increased by the quantity of foreign metal taken up by it, 

 would express the amount of substance which it has thrown off. 

 I took some pains to make experiments of this kind in hydrogen 

 gas ; but, with the battery I employed (50 Grove's elements of 

 the usual size), only a very imperfect arc of light was obtained 

 in hydrogen, and I did not arrive at any very exact results. 



I therefore replaced the hydrogen surrounding of the elec- 

 trodes by as nearly perfect a vacuum as possible, in which the 

 arc is obtained with decidedly greater facility. The electrodes, 

 screwed upon strong iron rods, were led through two large caout- 

 chouc stoppers, which tightly closed the two ends of a strong 

 cylinder such as is used for lamps. A glass tube with a glass 

 cock was also passed through one of the corks, and, for the pur- 

 pose of exhausting the cylinder, was connected with a Geissler 

 air-pump. The air in the cylinder was thus reduced to 1 or 2 

 millims. pressure. The electrodes were placed at an average 

 distance of 1 millim. At the commencement I introduced the 

 luminous arc, as proposed by Herschel*, by means of a Ley den 

 jar. Meanwhile it appeared that the operation could be as well 

 performed by taking advantage of the elasticity of the caoutchouc 

 and bringing the electrodes together by a momentary pressure 

 with the hands. They spring asunder again immediately, before 

 a perceptible quantity of hydrogen is developed in the voltameter 

 through which the current simultaneously passes ; and thus the 

 bright arc is instantly formed with the fine metallic dust flying 

 in all directions towards the sides of the cylinder. This spirting 

 of metallic dust-particles (which, as said, directly commences) is 

 characteristic for this, that the arc constitutes the only interme- 

 dium between the in every other respect separated electrodes, 

 and therefore proceeds in the manner desired. 



There is a series of metals which show themselves the least 

 convenient for these experiments; they are the easily fusible 

 ones, from which, with a somewhat continued action of the cur- 

 rent, large portions readily melt off and so render difficult the 

 determination of the quantities really separated in dust. It thus 

 happened in experiments with zinc, cadmium, lead, and tin. 

 * Pogg. Ann. vol. xlix. p. 122. 



