Chemistry and Physics. 99 



illustrations are good, and they include many useful graphic 

 curves. In short, this appears to be a remarkably able and mod- 

 ern book, which is well suited to arouse the interest of the student. 



h. l. w. 



6. A Treatise on General and Industrial Inorganic Chem- 

 istry ; by Dr. Ettore Molinari. Translated by Dr. Ernest 

 Fleitmann. Large 8vo, pp. 704. Philadelphia, 1912 (P. Blak- 

 iston's Son & Co. Price $6.00). — This English edition has been 

 translated from the third revised and amplified Italian edition. 

 The book is very interesting from the fact that it has been written 

 with the novel idea of teaching the theory of chemistry in con- 

 nection with an extensive treatment of the practical application 

 of the science. The first part of the book, comprising 125 pages, 

 is devoted strictly to theoretical chemistry, w T hile the remaining, 

 descriptive portion contains further theoretical discussions, but in 

 this part special attention is given to industrial chemistry. The 

 illustrations are numerous and good, and the book as a whole 

 appears to be a very creditable one. h. l. w. 



7. On the Discharge between Concentric Cylinders in Gases 

 at low Pressures. — In two earlier papers F. W. Aston has 

 given an account of his investigations upon the length of the 

 Crookes dark space and the relation between current and poten- 

 tial in the discharge between large plane aluminium electrodes 

 in different gases at various pressures. For all the chemically 

 active gases and for the members of the helium group, when the 

 latter were not extremely pure, it was found that the following 

 equations hold over a rather wide range 



d = t + ^'< I) v = E + -p- ' (II) 



D = length of dark space, P = gas pressure, V = potential differ- 

 ence between electrodes, and C = current density. The values 

 of the constants A, E, and F change markedly from one gas to 

 another, whereas B remains sensibly constant. Now, with plane 

 electrodes in a cylindrical glass tube, the current density for 

 points not too close to the glass w T alls will have the same value 

 throughout the length of the discharge, and hence no information 

 can be obtained as to the particular part of the discharge upon 

 which the value of the current factor B of the dark space depends. 

 On the other hand, if the parallel plane electrodes are replaced 

 by two coaxial cylinders the current density will vary from point 

 to point throughout the discharge, so that valuable information 

 about B and the nature of the discharge in general might be 

 expected. 



Recently Aston has carried out his suggestion, using hydro- 

 gen and oxygen. The outer electrode consisted of a thin, 

 aluminium sheet, which fitted close against the inner wall of a 

 glass tube. The inner electrode, made of the same metal, was 

 wound around the outside of a smaller glass tube. The electrodes 

 were maintained coaxial by means of the insulating supports of- 



