Chemistry and Physics. 477 



5. The Practical Methods of Organic Chemistry, by Ludwig 

 Gattermann. Translated by Schober and Babasinian. 12mo, 

 pp. 401. New York, 1914 (The Macmillan Company). — This 

 is the third American edition, corresponding to the eleventh Ger- 

 man edition, of a book that is so well known and so widely used 

 in connection with the preparation of organic compounds, that it 

 is only necessary to say that the new edition contains some 

 important but not very extensive additions. h. l. w. 



6. Spectrograph!/ of Pontgen Pays. — A spectrograph for X- 

 rays, giving lines which compare favorably in sharpness with 

 ordinary spark spectra, has been devised by Maurice de Brogue 

 and used very successfully by the inventor and by several other 

 investigators. A beam of X-rays is caused to pass through a 

 rectangular slit in a lead block and to fall upon the plane face of 

 a suitable crystal. This crystal is slowly rotated by clockwork 

 (or otherwise) around an axis which is parallel to the slit, which 

 lies in the reflecting surface of the crystal, and which intersects 

 the axis of the X-ray beam at the point of incidence. The crys- 

 tal behaves like a three-dimensional grating and brings the radia- 

 tions to foci whose centers lie on the arc of a circle passing 

 through the point of incidence on the crystal surface and having 

 a radius equal to the distance between the point of incidence and 

 the point where the beam of X-rays forms an effective slit. If a 

 photographic film is bent into the form of a cylinder containing 

 the arc just defined, the X-ray spectra will be recorded as the 

 crystal is slowly rotated. The glancing angle a and the wave- 

 length A. will satisfy the well-known relation nX = 2<#sina. It is 

 easy to show mathematically that, for small wave-lengths, the 

 spectra will be normal. By rotating the dispersing crystal in both 

 directions with respect to the incident beam, spectra of positive 

 and negative orders will be registered and hence any uncertainty 

 as regards the exact point of incidence can be avoided. In 

 general, sufficiently accurate results can be obtained by using a 

 plane photographic plate, placed as a mean chord of the focal 

 circle, instead of a cylindrical film. Furthermore, the apparatus 

 can be used as a direct vision spectroscope by substituting a suit- 

 able phosphorescent screen for the photographic plate. 



The negatives obtained by de Broglie are very clear, and 

 beautiful from the scientific standpoint. The general appearance 

 of the spectra may be briefly described as follows: They com- 

 mence at the short wave-length side with two bands which appear 

 to be continuous. The narrower band is very intense and has a 

 sharply defined boundary at the longer wave-length side. The 

 wider band is much weaker and shades off gradually towards the 

 longer wave-lengths. Near the outer edge this band is associated 

 with fine lines. The angle corresponding to the head of the 

 weaker band is about twice as large as the angle for the head of 

 the stronger band. The indefiniteness of the outer limit of the 

 weaker band makes it impossible to tell whether the factor is 

 exactl3 7 two, that is, whether the diffuse band is simply the second 



