DETERMINATION OF ALKALIES IN SILICATES. 397 



always to be under the mortar, and introduce into the crucible. 

 The crucible is now tapped gently upon the table and the con- 

 tents settled down. 



The crucible is then clasped by a metallic clamp in an 

 inclined position, or it is placed in the upper part of the 

 support referred to in the latter part of this article, leaving 

 outside about three fourths of an inch or one inch. By means 

 of a small Bunsen burner the heat is brought to bear just above 

 the top of the mixture, and gradually carried toward the lower 

 part, until the sal ammoniac is completely decomposed, which 

 takes about five minutes. Heat is then applied in the manner 

 suggested, either with the blast or with the burner referred to, 

 acting by its own draught, and the whole kept up to a bright- 

 red heat for from forty to sixty minutes. It is well to avoid 

 too intense a heat. 



The crucible is now allowed to cool, when the contents will 

 be found to be more or less agglomerated in the form of a semi- 

 fused mass. A glass rod or blunt steel point will most com- 

 monly detach the mass, which is then dropped into a platinum 

 or porcelain capsule of about one hundred and fifty centimetres 

 capacity, and sixty or eighty centimetres, and distilled water 

 added. After some time the mass will slack and crumble in 

 the manner of lime. Still better, this may be hastened by 

 bringing the contents of the capsule to the boiling-point either 

 over a lamp or water-bath ; at the same time water is put into 

 the crucible to slack out any small particles that may adhere 

 to it, and subsequently this is added to that in the capsule, 

 washing off the cover of the crucible also. 



After the mass is completely slacked the analysis may be 

 proceeded with. As a general thing, I prefer to allow the 

 digestion to continue six or eight hours, though this is not 

 necessary. 



If the contents of the crucible are not easily detached, do 

 not use very much force, as the crucible may be injured by it; 

 but fill the crucible to about two thirds its capacity with water, 

 bring it almost to the boiling-point, and lay it in the capsule 

 with the upper portion resting on the edge. The lime will 

 slack in the crucible, and then may be washed thoroughly into 

 the dish ; also, as before, the cover is to be washed off. 



We have now by this treatment with water the excess of 



