104 Professor Grenville A. J. Cole — On Flame- Reaction. 



The blue glass usually supplied with blowpipe-cabinets is far too 

 thin, and any strong sodium flame will appear through it as a violet 

 one. On using blue glass 5 mm. thick, all but the strongest light of 

 an intense sodium flame is cut off, and the column or band of flame 

 that does reach the eye appears blue and not violet. On securing, 

 after experiment, a blue glass, or combination of glasses, which gives 

 only this effect, potassium may be safely looked for, and will readily 

 be recognized, even alongside the blue flame due to the presence of 

 an unusual proportion of sodium. 



Lithium, it may be observed, is cut off by a much less thickness 

 of blue glass, and can generally, as in lepidolite and spodumene, 

 be recognized by the eye alone, when the assay is held in the very 

 outermost sheath of the Bunsen flame, or barely touching the flame 

 at all. 



The difficulty, however, in the case of potassium is that the flame 

 is often so feeble that some doubt exists as to its occurrence when 

 viewed through 5 mm. of blue glass. Hence intensification baa 

 been sought, in the case of silicates, by mixing the assay with 

 powdered gypsum, a method recommended by Bunsen. On thorough 

 heating, even 3 or 4 per cent, of potash reveals itself in this manner ; 

 and Professor Szabo ^ was confident that he could detect even 

 1 per cent. 



The great value of Szabo's results to geologists is their quantitative 

 character ; but his determinations of potassium involve the dipping 

 of the assay into powdered gypsum, instead of its complete 

 powdering together with the gypsum. The latter method I have 

 found to be far more certain ; but it is obviously impossible to pick 

 up again on the platinum loop, after powdering, the whole of the 

 assay selected, or a known bulk of it. Hence even the results with 

 gypsum have given little satisfaction in practice. 



It seemed, however, that decomposition of the assay in a bead of 

 sodium carbonate might get rid of the difficulties surrounding the 

 reaction. We should always have the satisfaction of knowing that 

 what we saw could not be due to sodium, for this flame would be 

 eliminated by testing our blue glass in each case on the bead alone. 

 Moreover, the most refractory silicates would be dealt with even 

 more completely than when intimately powdered up with gypsum. 



Since the simple support used in testing this reaction, and in all 

 such work in the laboratory of the Royal College of Science for 

 Ireland, was described in the Gteological Magazine,^ it may seem 

 appropriate to furnish the details of this later process here. 



The ordinary observations, as arranged by Szabo, may be gone 

 through first, on an assay of the dimensions used by that author. 

 In place of the observation with gypsum, I would venture to 

 substitute the following. In many cases, such as the determination 

 of the presence of potassium in the groundmass of a lava, it may 

 suffice as the only observation to be made. 



1 "Ueber eine neue Methode die Feldspathe zu bestimmen," p. 34 ; Budapest, 1876. 

 ^ G. Cole, "A Simple Apparatus for Flame-Eeactions " : Geol. Mag., 1888, p. 314. 



