1870.] 



Erbia and some other Earths. 



547 



which accompanies Bahr and Bunsen's paper were seen, but the lines were 

 more distinct when a small proportion of oxygen was admitted. With the 

 full proportion of oxygen, the light from the glowing erbia was more 

 intense, but the lines were not so well seen. Even with the intense heat 

 of the oxyhydrogen flame I was unable to trace the lines beyond the 

 limits of the solid erbia, though the line of sodium could be seen for some 

 distance from the erbia. I found, however, that the lines appeared more 

 distinct, in consequence, probably, of their being brighter relatively to the 

 parts of the continuous spectrum where they occur, when the slit was 

 directed from the side upon the gas immediately in front of the glowing 

 part of the erbia. 



The spectrum of bright lines obtained by means of the oxyhydrogen 

 flame agreed more completely with the absorption spectrum represented by 

 Bahr and Bunsen (No. 2 in their diagram) than the spectrum of bright 

 lines figured by those observers (No. 3). The most important differences 

 occurred in the band in the red, which showed two points of greatest 

 brightness, thus forming a double line with a little outstanding light, and 

 the line in the green at 65 of the scale, which was double, precisely as the 

 corresponding absorption-line is represented in spectrum No. 2 of the 

 diagram. 



Lime. — The experiments were made with the cylinders of lime prepared 

 for use with the oxyhydrogen blowpipe, and also with pieces of pure 

 caustic lime, but there was no sensible difference presented in the spec- 

 troscope. 



The bright lines consisted of a double line in the green, and several 

 bands in the orange and red, which were found to form a spectrum iden- 

 tical with that which is produced when chloride of calcium is heated in the 

 flame of a Bunsen's burner. 



When the spectroscope was directed to a point in the flame a little 

 above the incandescent portion of the lime, the lines appeared beyond the 

 bright continuous spectrum, showing that they are not produced by the 

 white-hot solid lime, but by the luminous vapour into which a portion of 

 the lime has been converted by the heat of the flame. 



Magnesia. — The commercial heavy oxide of magnesium was made into a 

 paste with distilled water, and formed into a small pellet upon the end of a 

 platinum wire. The pellet of magnesia was slowly dried, and then placed 

 in the oxyhydrogen flame. I was surprised to see a spectrum of bright 

 lines precisely similar to that which is produced by lime. Chloride of 

 magnesium, when introduced into the Bunsen flame, gave a similar spec- 

 trum. I record these results as the oxide and chloride were those sold as 

 pure. I found afterwards that a very small trace of lime may be detected 

 in magnesia by means of the oxyhydrogen flame. 



I then took metallic magnesium, which I had found by the spectroscope 

 to be nearly pure, and formed from it magnesia and chloride of magnesium. 



When this magnesia, formed into a small ball upon a wire, was sub- 



