DETERMINATION OF ALKALIES IN SILICATES. 399 



vent any possible loss by the spirting of the salt. After the 

 sal ammoniac has been driven off by gradually increasing the 

 heat the temperature of the dish is brought up to a point a 

 little below redness, the cover being off. (The cover can be 

 cleaned from any sal ammoniac that may have condensed upon 

 it by heating it over the lamp.) The capsule is again covered, 

 and when sufficiently cooled, and before becoming fully cold, 

 is placed on the balance and weighed. This weight gives as 

 chlorides the amount of alkalies contained in the mineral. 



If the chloride of lithia be present, it is necessary to weigh 

 rapidly, for this salt, being very deliquescent, takes moisture 

 rapidly. 



It not unfrequently happens that the chlorides at the end 

 of the analysis are more or less colored with a small amount 

 of carbon arising from certain constituents in carbonate of 

 ammonia; the quantity is usually very minute, and in no way 

 affects the accuracy of the analysis. In selecting pure car- 

 bonate of ammonia for analytical purposes it is well to take 

 specimens that are not colored by the action of light. 



It only remains now to separate the alkalies by the known 

 methods. Under this head I have made several observations 

 that at some future time may be published as soon as the results 

 are sufficiently definite. 



A SPECIAL ARRANGEMENT FOR HEATING THE CRUCIBLE BY GAS. 



The support and burner, where gas is to be had, are simple in 

 their character, and have been contrived after a great variety 

 of experiments with gas furnaces. The figure here given illus- 

 trates the stand, burner, crucible, etc., and is about one sixth 

 the natural size:* h is the stand with its rod g ; d is a brass 

 clamp with two holes at right-angles to each other, having two 

 binding screws; it slides on the rod g; the second hole is for a 

 round arm attached to b, the binding-screw e fixing it in any 

 position, b is a plate of cast-iron five to six mm. thick, ten to 

 eleven cm. long, and four and one half cm. broad, having a hole 

 in its center large enough to admit the crucible to within about 

 fifteen mm. of the cover without binding, a is the crucible 



*This apparatus can be obtained from Johnson, Matthey & Co., Hatton 

 Garden, London. 



