M. R. Buusi'u's Bloicpipe Experiments. 521 



The reason that lasufstein, which only contains 9 per cent, of 

 soda, gives a stronger soda reaction than nephchne, which con- 

 tains 15 per cent., is that it ah'eady contains sulphuric acid, 

 and can therefore only be compared with silicates containing no 

 sulphuric acid when these are fused with gypsum, when, as is 

 seen from the Table, the anomaly disappears. As sulphuric 

 acid, by giving rise to the formation of volatile sulphate, renders 

 the reaction more delicate, it is first necessary to ascertain 

 whether it is jjresent. This is effected by fusing a sample with 

 soda in the reducing flame, letting it cool in the dark part of the 

 tiame, and then testing it on polished silver. 



In testing a sample a splitter is brought into the flame, and 

 by the intensity of the bleaching of the iodide paper the place is 

 approxinjatively determined. To come nearer to the number, a 

 lighted candle is approached to the iodide paper, and the 

 distance observed at which the bleaching passes into red. The 

 nearer the candle can be placed, the lower in the series is the 

 silicate. With lasurstein, the candle can be brought within 3 

 or 3 inches without producing red. After this preliminary test, 

 two, or at most three, comparative observations will show the 

 place of the silicate. 



Lithia silicates nnist be tested for separately. The above soda 

 scale cannot be used, as the lithia flame gives rays which 

 redden the iodide paper : this is not the case with potash. 



Lithia silicates can only be compared amongst themselves ; 

 and lepidolite, petalite, and trijihane are best used as reagents. 

 Their deportment is as follows : — 



1 a. Lepidolite. — Easily fusible. In the oxidizing flame yel- 

 lowish red to the naked eye; in the reducing flame and the 

 nuJting-space yellow; with the indigo prism a strong, and with 

 gypsum a still stronger lithia reaction ; tolerably strong potash 

 reaction, still stronger with gypsum and the prism. Feebler 

 soda reaction than 2 a and 3 a. The varieties richer in fluorine 

 often give a stronger soda reaction than 2 a and 3 a. 



2 a. Petalite. — Pretty readily fusible with intumescence ; no 

 potash reaction ; feeble soda reaction ; with gypsum stronger 

 than 3 a, and feebler than 1 a. Otherwise like lepidolite. 



3 a. Triphane. — Fuses without intumescence. Only with 

 gypsum a feeble soda reaction, which is feebler than 2 a. On 

 the other hand, a stronger lithia reaction than 2 a : otherwise 

 like petalite. 



The proporti(jii of alkalies in these silicates is as follows : — 



Lepidolite. Petalite. Trii)liiinc. 



Lithia . 2-41 3-30 5-47 



Soda . 0-71 Ml) OK) 



Potash. 800 ... Oil 



