Chemistry and Physics. 523 



chemistry and Photochemistry are regarded as treating the trans- 

 formations between chemical energy on the one hand, and heat, 

 electricity and radiant energy on the other. The substantiality of 

 energy, its forms, its capacity and intensity factors and the laws 

 of its transformations are brought out and emphasized, the signifi- 

 cance of the intensity factor of chemical energy, the chemical 

 potential, in the theory of chemical equilibrium is made apparent, 

 the history of the energy doctrine is outlined. 



The "Thermochemistry" is very complete, both in theory and 

 data. The " Electrochemistry " is a brilliant piece of work. The 

 historical development, from Grotthus to the free-ion theory, 

 from Hittorf and Kohlrausch to Arrhenius and Ostwald, is most 

 interesting, and it is followed by a complete discussion of the 

 magnificent results in the theory of concentration currents and of 

 the galvanic cell, the whole treated from one point of view, as neces- 

 sary deductions from the energy laws. Many new conclusions 

 are drawn and confirmed by experiment; the whole reads like an 

 original paper and is inspiring in the extreme. The volume is 

 concluded by a similar presentation of the facts and theories of 

 Photochemistry. j. e. t. 



6. Simplification of Testa's Experiments. — The glowing of a 

 vacuum tube with or without electrodes can be shown by bringing 

 it in contact with one pole of a Ruhmkorff coil or in the neighbor- 

 hood of an insulated metallic plate which is connected with one 

 pole of the Ruhmkorff. If one pole of a small Ruhmkorff is 

 touched by the hand and a vacuum tube held in the other hand, it 

 can be made to glow. — Beiblatter zu den Annalen der Physik 

 und Chemie, p. 237. j. t. 



7. Loss of Electric Charges in diffuse light and in darkness. — 

 Edouard Brajstlt finds that a disc of polished aluminum, experi- 

 mented on a few days after being polished, slowly loses its charge. 

 If the disc has been freshly polished the loss is rapid, even in 

 diffuse light, and is only slightly diminished by surrounding it 

 with orange light, thus showing that the loss is not due to any 

 great extent to the refrangible rays of the spectrum. — Comptes 

 Rendus, April, 1893. j. t. 



8. Influence of the character of metallic p>oints on alternating 

 discharges of Electricity between them. — Wuetz states that iron 

 terminals give small sparks. Copper and copper alloys give strong 

 ones. An arc cannot be established between iron electrodes with a 

 difference of potential of l,00o volts. Steel, copper, phosphorus, 

 bronze, aluminum bronze, tin and nickel also give no result. 

 Zinc and also antimony resist a difference of potential of 1,000 

 volts. It is apparent that certain metals give off a metallic 

 vapor in the electric arc which lessens the resistance of the arc. 

 While other metals foi*m an oxide which diminishes the arc by 

 reason of its great resistance. The shorter this distance between 

 electrodes of zinc and antimony up to one millimeter, the less 

 permanent is the arc from an alternating current of 1,000 volts. If 

 the air gap is increased to 5 cm the arc is more permanent. — 

 Eumiere Electrique 45, p. 79, 83, 1892. j. t. 



Am. Jour. Sol— Third Series, Tol. XLV, No. 270.— June, 1893. 

 36 



