104 Prof. R. Bunsen on Flame Reactions. 



gives a yellowish-brown colour or precipitate on addition of an 

 excess of cold concentrated hydrochloric acid. 



(b) In the borax bead the vanadium compounds give in the 

 oxidizing flame a greenish yellow, in the reducing flame a green 

 colour. 



32. Manganese Compounds, 



(a) These give an amethystine-coloured bead in the oxidizing, 

 and a colourless bead in the reducing flame. 



(b) A green-coloured bead is formed on cooling after fusion 

 with soda, especially when some nitre is added; this, extracted 

 with water, yields a green solution, which turns red on addition 

 of acetic acid, and then often becomes colourless, with separation 

 of brown flocculi. 



33. Uranium Compounds. 



(a) These give a yellow bead in the oxidizing flame, which 

 becomes green in the reducing flame, especially on addition of 

 stannous chloride. These colours closely resemble those of the 

 iron compounds, but may easily be distinguished, at least if no 

 other colouring metallic oxide is present, by the fact that the 

 uranium bead, when incandescent, emits a bluish-green light 

 analogous to that which the uranium compounds exhibit when 

 fluorescing. Beads of lead-oxide, stannic acid, and a few other 

 substances exhibit a similar phenomenon when incandescent, but 

 they none of them yield, like the uranium compounds, a coloured 

 bead on cooling. 



(b) Heated gently on the platinum spiral with hyclropotassic 

 sulphate, the insoluble uranium compounds can be decomposed. 

 The melted mass is powdered with a few particles of crystallized 

 sodic carbonate, and the moistened mass is absorbed by filter- 

 paper. A brown spot is formed by addition of a drop of ferro- 

 cyanide to the moistened paper. 



34. Phosphorus Compounds. — The presence of phosphorus 

 may easily be detected, even when mixed with large quantities of 

 other substances, as follows : — 



(a) The sample having been ignited, is rubbed fine on the por- 

 celain plate, is introduced into a small glass tube of the thick- 

 ness of a straw ; into this tube, which is closed at the bottom, a 

 piece of magnesium wire, about one-fourth of an inch in length, 

 is placed so that it is covered by the powder. On heating the 

 tube, magnesium-phosphide is formed with incandescence. The 

 black contents of the tube powdered on the plate give, on moist- 

 ening with water, the highly characteristic smell of phosphuretted 

 hydrogen. A piece of sodium can be equally well used if mag- 

 nesium cannot be procured. 



(b) If it has been ascertained that the sample does not yield 



