66 Scientific Intelligence. 



the standpoint of the ionic theory, and comes from an assistant 

 in Professor Ostwald's laboratory. It is evident that the work 

 has been very carefully carried out on the proposed plan, and it 

 will be useful to those who desire to employ the modern theories 

 of solutions in teaching the subject. Perhaps it is doubtful if it 

 is advisable to give as much prominence to the doctrine of ions 

 and the law of mass-action as is given in this book, particularly 

 with beginners in the study of chemical analysis, but the tendency 

 of teachers seems to be in this direction. 



The equations in the ionic form, which are extensively used in 

 this book, appear more complicated and less easy to grasp than the 

 usual equations, on account of the separation of the ionic symbols 

 by the plus sign. For instance, the form of the usual equation, 



2 AgN03 -f K,C0,z=zAg,C03 + 2k:n-03, 



is changed to 



2Ag- + 2NO3' + CO3" + 2K-= Ag^COg + 2K- -I- 2NO3'. 



This last equation does not represent the actual conditions with 

 complete accuracy, because in moderately concentrated solutions 

 ionization is not complete, and moreover it is not as easy to see, 

 as in the first equation, what salts are mixed to produce the 

 reaction. It would seem preferable, if ions are to be marked, to 

 give equations some such form as the following one : 



2Ag-N03' + N'a/»C03"=:Ag,C03 -f 2Na-N03'. 



A somewhat loose statement is noticed in the explanation of 

 ionization (S. 13) where it is stated that "always an equal num- 

 ber (eine gleiche Zahl) of positive and negative ions is formed or 

 disappears." Of course these numbers vary according to valency. 



The author has not used the results of the more recent investi- 

 gations in all cases. If he had carefully consulted Fresenius's 

 last edition, he would probably have pointed out the difficulty of 

 detecting small quantities of silver chloride in the presence of 

 mercurous chloride, and would have given a method for over- 

 coming this trouble. He should have avoided the unreliable 

 method of testing for strontium, in the presence of much calcium, 

 with calcium sulphate solution. He should not have given the 

 formula NH^Hg^Cl, but NH,HgCl-fHg for the familiar black 

 substance produced by the action of ammonia upon mercurous 

 chloride. The formula SbClg-SCsCl should have been 2SbCl3 • 

 SCsCl, as has been shown by at least four different investigators, 

 the first of whom published his results in 1882. h. l. w. 



8. Reflection Roicer of Metals for Ultra-violet and Ultra-red 

 Rays. — E. Hagen and H. Rubens extend their previous work 

 on this subject, which extended from A= 450 to 700 /x/x. They 

 abandoned their previous photometric method and adopted a 

 heat method, consisting of the use of a linear thermal element 

 (H. Rubens, Zeitschr. f Instrumenterilc., 18, p. 65, 1898). This 

 heat method could be used as far as 221 /a/x; for the authors 



