306 Royal Society : — Dr. W. Huggins on the Spectra 



The behaviour of silver, therefore, is similar to that of the other 

 metals of the monad group. Now the difference in basic relations 

 which is known to exist between the oxides of the monatomic and 

 polyatomic metals is in accordance with the distinction which the 

 spectroscope shows to exist in the behaviour of the chlorides : the 

 chlorides of the polyatomic metals would be more likely to split up 

 in the presence of water into oxides and hydrochloric acid. 



In the case of some of the oxides and chlorides, one or more of the 

 lines appeared to agree with corresponding lines in the metallic 

 spectra ; it may therefore be, that under some circumstances, as in 

 the case of magnesium burning in air, the metallic vapour and the 

 volatilized oxide may be simultaneously present. 



Dr. Reynolds's Experiments. 



" After you observed the occurrence of two bright lines in the 

 spectrum of the light emitted by incandescent lime, you recollect we 

 identified these as belonging to calcium. At the time we supposed 

 that these lines were produced by the ignition of the vapour of 

 some volatile calcium compound probably present as an impurity in 

 the samples of lime used in the experiments. If this explanation were 

 found to be true for lime, the bright lines seen in the spectrum of 

 erbia might possibly be accounted for in a similar manner. In 

 order to examine the matter fully, I arranged the experiments de- 

 scribed below. 



" I selected two oxides for comparison with erbia, viz. lime and 

 magnesia. As it seemed desirable to prepare these oxides in precisely 

 the same manner as the erbia, some calcium and magnesium nitrates 

 were made chemically pure to ordinary tests, and then used in the 

 preparation of the respective oxides. 



" The oxyhydrogen flame was employed as the chief source of heat. 

 The hydrogen was made from zinc and sulphuric acid in the usual 

 way, and the oxygen from potassium chlorate. As both gases are 

 certain to be contaminated with traces of acids, I took the pre- 

 caution of passing each gas through a long tube filled with fragments 

 of solid potassium hydrate. If this plan were not adopted, the traces 

 of acid which would find their way into the hydrogen or oxyhydrogen 

 flame might produce volatile compounds with the earths, and so lead 

 to mistakes. 



" 1. Experiments with Magnesia. — A loop of stout platinum wire 

 was moistened with syrupy phosphoric acid, and some magnesium 

 nitrate made to adhere. The nitrate was then heated in the hydro- 

 gen flame, and a residue of magnesia obtained. No lines were ob-" 

 served in the spectrum of the light emitted by the incandescent earth; 

 and when the latter was intensely heated in the oxyhydrogen jet, 

 only a continuous spectrum was seen*. 



* " Since writing the above, I have succeeded in observing the bright lines de- 

 scribed by Mr. Huggins as occurring in the spectrum of the flame surrounding 

 the incandescent magnesia. In the earlier experiments I probably admitted 

 too much oxygen to the mixed gas-flame in the first instance." 



