550 



Dr. W. Huggins on the Spectra of 



[June 16, 



flame, but no lines were visible. When, however, the moistened chloride 

 was placed on cotton and subjected to the induction-spark without a 

 jar, the true metallic spectrum was seen, as when silver electrodes are 

 used. 



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 would 

 be 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- 

 be, therefore, that under some circumstances, as in the case of magnesium 

 burning in air, the metallic vapour and the volatilized oxide maybe simul- 

 taneously 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 com- 

 pound probably present as an impurity in the sample of limes used in the 

 experiments. If this explanation was 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 described 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 con- 

 taminated with traces of acids, I took the precaution 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 hydrogen flame, and 

 a residue of magnesia obtained. No lines were observed in the spectrum 

 of the light emitted by the incandescent earth, and when the latter was in- 



