( 92 ) 



well-known method of Ingenhousz, by measurement of the length 

 of the melted off waxy layer which was pnt on the surface of 

 cylindrical rods of bismuth, cut // and J_ to the main axis, whilst 

 the one end was plunged into mercury heated at 150^ For the 

 average value of the quotient of the main conductivities — perpen- 

 dicular and normal to the main axis — he found the value 1,08. 

 Jannk.ttaz's rule applies in this case, because the complete cleavability 

 of ditrigonal bismuth takes place along |111| (Miller), therefore, 

 perpendicularly to the main axis. Jannkttaz ^) has applied the 

 SÉNARMONT method to bismuth. He states that in bismuth the ellipses 

 have a great eccentricity but he did not take, however, exact 

 measurements. 



A short time ago, Lownds^) has again applied the Sénarmont method 

 to bismuth. He finds for the quotient of the demi-ellipsoidal axes 

 1.19 and, therefore for the quotient of the conductivities 1.42. 



The last research is from Perrot "). By the Senarmont method 

 he finds as the axial quotient of the ellipses about J. 17 and conse- 

 quently for the quotient of the conductivities J_ and // axis 1,368, 

 which agrees foirly well with the figure found by Lownds. Secondly, 

 Perrot determined the said quotient by a method j)roposed by 

 C. SoRET, which had been previously recommended by Thoulet^), 

 namely, by measuring the time which elapses between the moments 

 when two substances with known melting points 0-^ and d-^ placed 

 at a given distance at ditferent sides of a block of the substance 

 under examination begin to melt. As indices were used; ct-NapJdyla- 

 mine (i^' = 50° C), o-NitroanUhie (<*> = 66^C.), and NaphtJialene 

 (^ = 79° C). 



As the mean of all the observations, Perrot finds as the quotient 

 of the main conductivities 1,3683, which agrees perfectly with his 

 result obtained by Sp;narmont's method. 



He, however, rightly observes that this concordance between the 



two results is quite an nccldental o/z^^ and that the method of Thoulet 



and SoRET must not be considered to hold in all cases. The proof 



thereof has been given by Cailler in a theoretical paper ; '') the 



agreement is caused here by the accidental small value of a quotient 



hi 



— , in which / represents the thickness ot the little plate of bismuth 

 k 



^) Jannettaz, Ann. cle chim. pliys. 29. 39. (1873). 



2) L. Lownds, Phil. Magaz. V. 152. (1903). 



'^) L. Perrot, Archiv. d. Science phys. et nat. Geneve (1904 . (4). 18. 445. 



4) Thoulet, Ann. de Chim. Phys. (5). 26. 261. (1882) 



s) G. Gailler, Archiv. de Scienc. phys. et nat. Geneve (1904). (4). 18. 457. 



