CHEMICAL SCIENCE. 171 



experiments, arising from electrical heat and light, as well as from 

 the disengaged gases, is diminished. One cannot be too securely de- 

 fended, however, especially from the electrical light, when it is raised 

 to a certain degree of intensity. The light from 100 elements might 

 occasion serious danger to the eyes ; but this danger is much greater 

 when the light from a battery of 600 elements is encountered. Even 

 in approaching it only for an instant, there is danger of a violent head- 

 ache and pain in the eyes, and the face, moreover, is burnt, as by a 

 powerful coup de soldi. M. Despretz and his assistants have in the 

 course of his experiments been powerfully affected by it, and now, 

 although well protected, one person is not permitted to conduct a 

 whole series of experiments. 



In some of his experiments, M. Despretz joined to a Bunsen's bat- 

 tery of 600 elements another battery of 135 elements, directing the 

 fire of the first battery directly upon the object, while it was heated 

 by the other. Such was its intensity, that when a crucible made of 

 retort charcoal, containing pieces of sugar charcoal, was submitted to 

 its action, in an instant the sugar charcoal was consumed, the crucible 

 reduced to bent fragments, and the whole converted into graphite. In 

 this connection, Despretz mentions that acicular rods of retort char- 

 coal may be converted into graphite by the heat of an enamellers 

 lamp in the course of a few minutes, and this change sometimes even 

 takes place in the retorts where it is produced. It is even probable 

 that, after a sufficiently long lime, the same transformation might be 

 accomplished at a much lower temperature than that of the retorts in 

 which gas for lighting is made. This fact, in a geological point of 

 view, is interesting. The size of the pieces of charcoal fused by 

 Despretz have in some instances exceeded that of a large pea. 



Various experiments have been also made in connection with these 

 powerful batteries upon the diamond. For this purpose, the dia- 

 monds, after having been heated gradually, to prevent a splitting when 

 suddenly exposed to a high temperature, were inclosed in tubes of 

 charcoal, seven or eight millimetres in external diameter, closed with 

 charcoal stoppers. When exposed to a comparatively feeble action of 

 the battery, the diamond changes color, becoming grayish-black, con- 

 ducts electricity, has the appearance of graphite, or black-lead, and 

 leaves a mark upon paper. The tube in this case was maintained at 

 a white heat for twenty minutes. In a second experiment it was 

 found that a diamond exposed to the same degree of heat for seventeen 

 minutes did not experience much, if any, alteration, but still scratched 

 glass, and was a non-conductor of electricity. A diamond of 2.5 mil- 

 limetres in diameter, exposed to a stronger action of the battery, that 

 of 600 elements, immediately fused, and when cooled could be crushed 

 in the fingers. In another experiment, six small diamonds were ex- 

 posed to the full strength of the battery for Ik minutes ; two of the 

 diamonds had then the appearance of graphite, and the remainder 

 were reduced to dust. The change which the diamond was found to 

 undergo on exposure to great heat was in general as follows. It 

 first changes to charcoal, from a non-conducting to a conducting body, 

 then to graphite, and, if the heat be sustained, it gives rise to small 

 fused globules. 



