560 Scientific Intelligence. 



nomenclature seems to be slighted. On the other hand, it maybe 

 said to its advantage that the book contains but little of the 

 unessential^, with which many of the elementary text books are 

 encumbered. a. j. hill. 



7. An Introduction to the Study of Organic Chemistry ; by 

 H. T. Clark. 12mo, pp. 484. London, 1914 (Longmans, Green 

 and Co.). — In preparing this new text book the author has con- 

 fined himself to the discussion of the important types of organic 

 compounds, clearly showing their relationships with each other 

 and their important reactions. He has generally avoided giving 

 the details of preparations, as being out of place in an elementary 

 text-book. The material included, while being distinctly funda- 

 mental in character, covers the field quite satisfactorily, and 

 includes some quite modern facts. One of the early chapters of 

 the book is devoted to an interesting and instructive survey of 

 the classes of compounds derived from ordinary alcohol. The 

 book is one which teachers of elementary organic chemistry 

 should find of interest. n. a. shepard. 



8. The Relation between Absorption and Wave-length of 

 X-rays. — By making use of the experimental data obtained by 

 Barkla, Darwin, Moseley, and others, M. Siegbahn has brought 

 out some important facts concerning the functional dependence 

 of the absorption upon the wave-length of Rontgen-rays. When 

 the logarithms of the wave-lengths of the K type of radiation 

 from calcium, iron, cobalt, nickel, copper, zinc, molybdenum, and 

 silver are plotted as abscissse with the logarithms of the corre- 

 sponding values of the ratio (— ] of the absorption coefficient (/a) 



for aluminium to the density (<r) as ordinates, the points are found 

 to lie on a straight line. In this case the wave-lengths vary from 

 3-368 X 10 _8 cm. to 0*560 X 10 -8 cm., or more than two octaves, while 

 the absorption ratio changes from 435 to 2-5 cm 2 /gram. This fact 



may be expressed by the equation ( — J = A . \ x , where A and x 



are constants. A depends upon the radiator itself whereas x is a 

 general constant having the value 3, very nearly. When the 

 same kind of diagram is plotted for wave-lengths greater than 

 those of the fluorescent or homogeneous characteristic radiations 

 the same formula with the same value of x is found to hold good. 

 The lines are straight for all wave-lengths outside of the regions 

 of selective absorption. At the regions of selective absorption 

 the straight lines are shifted bodity parallel to themselves. In 

 other words, for a given radiator possessing a band of selective 

 absorption, within the interval of X-rays whose wave-lengths 

 have been determined, the symbol A has one value below the 

 band and another above the same. The values of A for the 

 extreme elements carbon and tin are 1*5 and 81 respectively. 

 Again, the same formula applies to the following gases and vapors, 



