Notices respecting New Books. 475 



the presence of liquid water a chemical change does take 

 place in all these cases. 



Finally, it may be pointed out that the experiments of Mr. 

 F. Wilson, of Keble College, and myself on the action of dried 

 hydrochloric-acid gas on various carbonates, together with the 

 experiments herein described, go to show that the compounds 

 represented by the formula HC1 and the formula H 2 S are not 

 (as is. usually supposed) acids, but rather that they are acid 

 anhydrides, not of the same order although of the same class 

 as pentoxide of phosphorus or sulphuric anhydride. Just as 

 in the case of many organic acids (for example, gly collie or 

 lactic acids), we have more than one anhydride, so also in the 

 case of the true sulphuric acid we may have the anhydride 

 80 3 and the anhydride H 2 S0 4 . Perkin, from a study of the 

 magnetic rotation of sulphuric and nitric acids, concludes 

 that the formulae H 2 S0 4 and HN0 3 represent, not the acids, 

 but anhydrides (J. 0. S. 1887, p. 808, and 1889, p. 680). 

 The pure compound H 2 S0 4 , as is well known, does not 

 act on blue litmus*, and probably is incapable of forming 

 salts ; and it seems probable, from the researches of Veley 

 on nitric acid |, that this acid also, when in the pure state 

 and free from nitrous acid, is likewise incapable of form- 

 ing salts. So that the two criteria of true acids, namely, 

 that they should be capable of turning blue litmus red, and 

 also be capable of forming salts, fails in the cases of the mole- 

 cules HC1 % and H 2 S, and apparently also in the case of the 

 molecules H 2 S0 4 and HN0 3 . 



In conclusion, I wish to express my indebtedness to Mr. 

 Y. H. Veley, M.A., for suggesting this investigation to me 

 and for much valuable advice given during its progress. 



University Laboratory, Oxford. 



LIY. Notices respecting New Books. 



Index of Spectra. Appendix 0. By W. Marshall Watts, 

 D.Sc, F.I.O., Senior Science Master in the Gigglesiuick Grammar 

 School. Manchester : Abel Heywood & Son, 1892. 



r PTIE present appendix to Dr. Watts's Index of Spectra contains 

 -*- some of the most important measurements recently made in 

 connexion with spectroscopic work. By far the larger part of the 

 book is occupied by the collected results of various observers on the 

 spectrum of iron when volatilized in the electric arc. The numbers 

 of Kayser and Eunge, Eowland, Thalen, and Miiller and Kempf 



* Marsh, ' Chem. News,' lxi. p. 2. f Phil. Trans. 1891, p. '279. 



% Julius Thomsen concludes from thermocheniical considerations that 

 the formula of the acid is IT CIO. Tossihlv the true hydrosulphuric 

 acid is H,SO. 



