On the Qua nti vale nee of Oxygen. 403 



quenched steel for a period of years, produces a diminution 

 of hardness about equal to that of 100° C. acting for a period 

 of hours. Similar results have been suspected for magnetic 

 measurements ; but such results are very much less easily 

 interpretable than the electrical data of Table IV. For 

 earlier measurements * prove conclusively that ihe electrical 

 variations in question are sufficient evidence for the occur- 

 rence of concomitant changes of hardness, volume, carbura- 

 tion, &c. Finally, the above results show that the method of 

 tempering magnets proposed by Dr. Strouhal and myself f 

 warrants the steel against secular structural instability for a 

 time certainly exceeding three years. 



Phvs. Lab. U. S. G. S., 



Washington, D.C. 



XLV. Evidence of the Quantivalence of Oxygen derived from 

 the Study of the Azo-Naphthol Compounds. By Raphael 

 Meldola, F.R.S., F.C.S., F.I.C., Professor of Chemistry 

 in the City and Guilds of London Institute, Finsbury Tech- 

 nical College %. 



IT has long been known that by the action of diazo-salts 

 upon the naphthols and naphthylamines two parallel series 

 of azo-derivatives are obtained which possess different charac- 

 ters according as they belong to the a- or /3-series. Thus the 

 azo-derivatives of a-naphthol are distinctly phenolic in cha- 

 racter, dissolving readily in alkalies and being thrown out 

 again by acids in accordance with the general properties of all 

 the oxyazo-compounds. Similarly, the azo-derivatives of a- 

 naphthylamine have the general characters of true amidoazo- 

 compounds ; the NH 2 -group, which they undoubtedly contain, 

 can be readily diazotized, and by this means a series of second- 

 ary azo-compounds can be prepared. When the azo-derivatives 

 of the /3-series are compared with the corresponding a-cora- 

 pounds marked differences are found to exist. These differences 

 between the two classes of azo-compounds are too distinct to 

 be attributed to the isomerism of position only — there are, in 

 addition to such physical differences as those of melting-point 

 and crystalline form, deeper-seated chemical distinctions which 

 have suggested a different constitution for the two classes of 

 compounds. 



* Cf. this Magazine, August, 

 t Bull. U. S. G. S., No. 14, p. 171, 1885. 



X Communicated by the Author, having been read at the Bath Meeting 

 of the British Association, in connexion with the discussion on Valency. 



