170 Soil Analysis [288, 289 



with calcic carbonate and ammonium chloride, which break 

 down the insoluble silicates and set free the alkalis in the form 

 of alkaline chlorides. 



Fusion with Alkaline Carbonates 



288. Preparation of Fusion Mixture. — This mixture of 

 Na 2 C0 3 and K 2 C0 3 in molecular proportions may be pre- 

 pared either by mixing in a mortar 10 grams of sodium carbon- 

 ate and 1 3 grams of potassium carbonate, both of which have 

 been recently fused, or by igniting Rochelle salt in a platinum 

 dish, extracting the charred mass with water, and evaporating 

 the liquid to dryness. 



In any case the mixture must be dried perfectly before 

 using. 



289. The Operation. — Weigh out about a gram of 

 the substance in a platinum dish, ignite, and weigh again (para- 

 graph 285). Weigh out roughly 5 grams of dry fusion mixture 

 into a deep platinum crucible. Pour the weighed quantity of 

 1 insoluble matter ' on top of the fusion mixture, sweeping in 

 the last portions with a small camel's-hair brush. Now stir up 

 all the contents of the crucible with a stout piece of copper 

 wire until they are fairly mixed. Brush back into the crucible 

 any traces which may adhere to the wire. Place the cover 

 loosely on top of the crucible, and heat it on a pipe-clay triangle 

 over a Bunsen burner until the whole mass is fused. Continue 

 this heating until effervescence becomes subdued, then transfer 

 the crucible to a Fletcher muffle furnace (fig. 17), and keep at 

 a bright-red heat for forty minutes. Allow it to cool just below 

 redness, then cool rapidly by placing on a cold iron plate. 

 This will induce the vitrified mass to become very brittle. 

 When quite cool, place the crucible at the bottom of a 12-oz. 

 beaker, covered by a clock glass, and from a wash bottle fill the 



