OCTOBEB 22, 1909] 



SCIENCE 



567 



heat i3 absorbed in the process, then a rise in 

 temperature would increase rather than de- 

 crease their stability. 



On the other hand, the authors reason that 

 the assumption of compounds between solute 

 and solvent, or the assumption of solvates, is 

 in full accord with the observations of Hart- 

 ley, for not only would rise of temperature 

 tend to dissociate the solvates — but so would 

 increasing concentration of solute. Here 

 again, and for the same reason, it would seem 

 that the argument, though reasonable, is not 

 absolutely convincing, for it is by no means 

 certain that a rise of temperature always ac- 

 companies the formation of solvates. 



Another method of attack adopted by the 

 authors was to study the absorption spectra of 

 solutions of salts in ether, acetone and alcohol, 

 and in mixtures of these solvents with water. 

 Many salts when dissolved in these non- 

 aqueous solvents gave different absorption 

 spectra for different salts of the same colored 

 ion, but the spectrum of any one salt was dif- 

 ferent in different solvents. In mixtures of 

 water with non-aqueous solvents, many salts, 

 like neodymium chloride, for instance, showed 

 no marked change in the spectrum when the 

 amount of water was varied from 100 per 

 cent, to 15 per cent. But as the amount of 

 water was still further reduced, the spectrum 

 was found to consist of a superposition of the 

 spectrum of the aqueous upon that of the non- 

 aqueous solution. Similarly, when praseodym- 

 ium chloride was dissolved in mixtures of 

 water and of ethyl or methyl alcohol the same 

 sort of change was in general observed, except 

 that in the alcoholic solutions there appeared 

 an entirely new and very brilliant band in 

 the ultra-violet, having no analog whatever in 

 the spectrum of the aqueous solution. The 

 conclusion is drawn that these facts and others 

 of a similar nature are inexplicable on any 

 other than the solvate theory of solutions — 

 and further, that solvates of both undissoci- 

 ated molecules and of ions are formed. In 

 the case of cobalt and copper salts, the au- 

 thors conclude that a series of solvates of 

 varying complexity are formed, while in the 

 solutions of the rare earth which were studied 

 there exists but a single solvate. 



Finally it was observed that neodymium 

 nitrate and neodymium chloride have very 

 different spectra in concentrated aqueous so- 

 lutions, and that on dilution, the spectrum of 

 the chloride changes but slightly, while that 

 of the nitrate changes considerably and be- 

 comes identical with that of the chloride. 

 The authors explain this phenomenon as fol- 

 lows. The nitrate radical, consisting of 

 twelve atoms, is very much more complicated 

 than the chloride radical, and hence would 

 affect the light vibrations of the neodymium 

 atom to a much greater extent. The effect of 

 increasing solvation would, on the one hand, 

 be of less relative importance to the nitrate 

 than the chloride molecule, and, on the other 

 hand, the effect of dissociation, that is, the 

 separation of the nitrate radical from the 

 neodymium atom, would produce much gi'eater 

 changes in its absorption spectrum than the 

 removal of the chloride or bromide ions. 



It can be seen from this cursory review how 

 promising and yet how difficult is this line of 

 attack. With the splendid spectrophotographs 

 furnished by this investigation as a guide, 

 still more valuable results might be antici- 

 pated from an accurate spectrophotometric 

 study of the same solutions. The above quali- 

 tative tests of the various theories might then 

 be supplemented by strictly quantitative ones. 

 Arthur B. Lamb 



The Genera of Fungi. By Frederic Edward 

 Clements, Ph.D., Professor of Botany and 

 Head of the Department of Botany in the 

 University of Minnesota. Pp. iv -f- 227, 

 octavo. Minneapolis, The H. W. Wilson 

 Company. 1909. $2.00. 

 This long-expected key to Saccardo's " Syl- 

 loge Fungorum " has now appeared from the 

 press, as a thinnish octavo volume, bound in 

 plain green cloth. It is not so large as to be 

 unhandy in the using, and yet it is large 

 enough to secure that respect from librarians 

 and library users that its usefulness demands. 

 In the time that has elapsed since the publica- 

 tion of the mimeographed edition a couple of 

 years ago, the author has enlarged its scope, 

 80 that now a number of things are included 

 that were not found in the original work. 



