Chemistry and Physics. 481 



tion of complex compounds. The seventh chapter is devoted to 

 concrete examples of the methods discussed in the earlier pages. 

 The remaining chapters deal with ammoniacal salt solutions, 

 with certain cobalt and copper solutions, and with some special 

 cases of equilibrium. The " hydrate theory " is touched upon iu 

 an appendix. The chemical and mathematical equations and 

 formulae are clearly and accurately printed, and errors in the 

 original articles have been carefully corrected. The general use- 

 fulness of the compilation is increased by the inclusion of numer- 

 ous bibliographical references and of author and subject indices. 



h. s. U\ 



9. Lichtmessungen mit Selen / by Willy Jaenichen. Pp 

 viii, 76, with 22 figures and 5 plates. Berlin-Nikolassee, 1914 

 (Administration der " Zeitschrift fur Feinmechanik "). — In the 

 first part of this little book (pages 8-30) an account is given of 

 fifteen different types of apparatus and methods which have been 

 proposed for making determinations of the intensity of light by 

 the aid of selenium. The second part deals with the apparatus 

 designed by the author and with the experimental tests made by 

 him. The text concludes with final deductions concerning the 

 usefulness of selenium as regards (a) accuracy of measurements 

 and (b) color-sensitivity. Since the material has been presented 

 with care and since the folding plates show a relatively large 

 number of useful and instructive curves, the monograph should 

 be gladly received by all who are interested in the practical 

 applications of selenium. h. s. it. 



10. The Crystalline Structure of Copper. — The chief difficulty 

 encountered in the investigation of copper by means of the 

 X-ray spectrograph arises from the fact that native crystals have 

 faces which are too much warped and distorted to produce the 

 necessary " reflections " of the Kontgen rays. The experimental 

 problem has been recently solved by W. Lawrence Bragg. He 

 first attempted to produce artificial faces by grinding, but this 

 process was found to be of no avail because it destroyed the 

 crystalline character of the surface and thus prevented the reflec- 

 tion of the short electromagnetic waves. " It was observed, how- 

 ever, that when the crystal was placed in nitric acid until the 

 surface was eaten away to an extent of perhaps 1/4 millimetre, 

 the faces were etched deeply into numerous parallel facets, which 

 all reflected the light simultaneously in the usual way." "This 

 suggested that, internally the crystal structure was perfect, and 

 showed further that in some cases the whole specimen was com- 

 posed of a single crystal." "Moreover, in this case the surface 

 layers are not pulled about, and so are capable of reflecting the 

 X-rays falling on them." 



Since copper crystallizes in the holohedral class of the cubic 

 system it was natural to assume, as a working hypothesis, that 

 the copper atoms are arranged at the corners of cubes, thus form- 

 ing a simple cube lattice. The predicted glancing angles for the 

 palladium rays can then be calculated as follows. First, the dis- 



