407 



§ II. Chemical Science. 



1. On the Specific Heat of Elastic Fluid*. — This subject, which 

 has been under investigation at various times by MM. Laroche and 

 Berard, Haycraft, De la Rive, and Marcet, has been taken up 

 by M. Dulong, who has applied to it a new method of investiga- 

 tion dependent upon the velocity of sound in the different gases. 

 La Place shewed that the velocity of the sound in air or other 

 elastic media, was importantly influenced and increased above the 

 expected velocity by the heat evolved, as the vibrations producing 

 sound passed through the air ; and M. Dulong, by examining and 

 comparing the sounds produced by different gases, has endeavoured 

 to ascertain whether this element is the same in all of them. He 

 arrives at this general law, remarkable for its simplicity, i. That 

 equal volumes of all elastic fluids taken at the same temperature 

 and pressure, when compressed or expanded suddenly by a fraction 

 of their volume, disengage or absorb the same absolute quantity of 

 heat. ii. That the variations of temperature which result, are in 

 the inverse ratio of the specific heat of a constant volume. — Ann. 

 de Chimie, xli. 113. 



2. Supposed Influence of Magnetism over Chemical or Crystal- 

 lizing Powers. — The investigation of this influence, which has been 

 repeatedly asserted and denied, has been undertaken in a very care- 

 ful and particular manner by Professor Erdmann. . He first points 

 out the number of delicate perturbing causes which may and have 

 occasionally led to mistakes, pointing out the effects produced by 

 irregularity in the wires — handling them with the uncovered fin- 

 gers, &c. &c. ; and especially states that many repetitions of each 

 experiment should be made. The bars and magnets which he had 

 occasion to use were very powerful, some of them competent to lift 

 80 pounds. 



i. In experiments made to ascertain the oxidation of iron wire, 

 even under the influence of terrestrial magnetism, it was ultimately 

 proved, i. That the oxidation of iron placed under water is not at all 

 influenced by terrestrial magnetism ; there is no point of the horizon 

 towards which it is more strongly or quickly produced than towards 

 another, ii. The oxidation arising from unequal contexture of the 

 iron always begins at the points where the wire is in contact with 

 other bodies, not only metals, but even wax or baked earth, iii. 

 Diffuse daylight, or the weakened rays of a winter's sun, neither 

 retard nor assist oxidation, provided they are accompanied by no 

 change of temperature. 



ii. In experiments made with magnetized wires the results were 

 the same ; no difference of oxidation occurred at the two poles or 

 other parts. 



iii. In experiments on the reduction of metals by the humid pro- 



