Spectroscopic Examination of Silicates. 325 



could not be employed in spectroscopic work, while an easily 

 fusible chloride would be well adapted to it. The plan was 

 therefore adopted of mixing a small quantity of the finely 

 powdered mineral with an alcoholic paste of chemically pure 

 calcic chloride, and exposing a pellet of the pasty mass, on 

 a platinum loop, to the outer fljime of a Buusen burner, 

 before the slit of the spectroscope. 



This, it will be seen at once, is a return to the plan pro- 

 posed maijy years ago, by Prof. Henry Wurtz, for effecting 

 the decomposition of silicates and the extraction of their 

 alkalies. For some reasons unknown, this method, which 

 would seem to be an excellent one, does not appear to have 

 come into general use. It will be found, however, that in 

 its novel application to spectroscopic work, it eflects the 

 desired object with such easjs and rapidity, and with so small 

 an expenditure of reagent and material, that hereafter the 

 mineralogist will wish to add this reagent to those in most 

 constant use. The calcic chloride paste is most conveniently 

 preserved in a small wide-mouthed bottle, stoppered care- 

 fully to prevent the evaporation of the alcohol. There is 

 the disadvantage in its practical working, that the calcium 

 spectrum is always present : and the difficulty of preparing 

 and using such a reagent in a way that will exclude the 

 presence of minute quantities of sodium, is so great, that 

 the presence or absence of the sodium band cannot be re- 

 garded as demonstrating the presence or absence of sodium 

 in the mineral under examination. On the other band, an 

 extremely small quantity of the mineral is required. In 

 most cases it is sufficient to select a part of the mineral 

 which appears to be perfectly pure and unaltered, and to 

 rub off as much of the powder (with the corner of a file) as 

 could be taken on the end of a small knife-blade. This is 

 then rubbed up, successively, with either an equal amount 

 of the paste, or twice, thrice, or four times that amount, as 

 may be found necessary. Generally an equal amount will 

 be sufficient. An attempt was made to substitute magnesic 



