M. R. Bunscn's Blowpipe Eaperiinents. 519 



the follovviug minerals : — Orthoclase, and its varieties Sauidine 

 and Adularia, Leacite, Labradoiite ; Albite and Oligoclase, 

 Anorthite, Nepheline, Hauyne, and Lasurstein ; Petalite, Lepido- 

 lite, and Triphane. These are divided into two groups — those 

 containing hthia, and tliose in which it is absent. It is first 

 ascertained to which group the sample belongs^ by exposing it 

 with gypsum in the melting-space side by side with a specimen 

 of pure potash, and viewing the two flames through the indigo 

 prism. If the sample contains lithia, its flame at that part of 

 the prism at which the soda colour vanishes, appears red against 

 the cornflower-blue of the potash. With thicker layers of in- 

 digo the red of the lithia gradually lessens in intensity, while 

 the cornflower-blue of the potash passes through violet into red, 

 which, with a certain thickness of the indigo layers, is quite like 

 the colour of the lithia. If no lithia is found, the sample be- 

 longs to the flrst group, in the other case to the second. 



The individual minerals of the first group are recognized by 

 comparing them with each other according to their relative pro- 

 portions of potash and soda. A standard series of felspathic 

 minerals is selected, and arranged according to the soda they 

 contain. Buusen uses the following series, and distinguishes 

 them by the numbers placed over the analyses : — 



These silicates are heated, powdered, and arranged according 

 to their numbers, in small bottles. If one of these standard 

 silicates and the sample to be tested, either with or without 

 gypsum, be simultaneously placed side by side in the melting- 

 space, so that, besides the tests themselves, small but equal 

 lengths of the platinum wire are ignited, the iodide of mer- 

 cury paper before the flame appears more or less bleached. 

 If the sample be now removed from the flame, and the paper 

 exhibits a distinct passage to red, the sample contains more 

 soda than the staudard silicate. If the paper is whiter, the 



