290, 291] Fusion with Alkaline Carbonates 171 



crucible with hydrochloric acid (equal parts acid and water). 

 When effervescence has ceased, turn the beaker so as to lay the 

 crucible on its side, and add more acid until the crucible is 

 quite free from solid matter. Next remove the crucible with a 

 glass rod and wash it thoroughly with hot water, adding the 

 washings to the acid solution. 



All the silica in the portion of soil taken will be in the 

 gelatinous hydrated state. The liquid must be evaporated to 

 dryness on the water bath, then heated on the sand bath to 

 render all silica insoluble. A few c.c. of strong HC1 must be 

 added, to moisten the whole mass, and then 50 c.c. of weak 

 acid. After evaporating to about half bulk on the water bath, 

 the silica must be filtered off, dried, ignited, and weighed, and 

 the filtrate must be analysed according to the table in para- 

 graph 272. 



DETERMINATION OF 'INSOLUBLE' ALKALIS 



290. Preparation of Pure Calcic Carbonate. — Dissolve 

 Iceland spar or good marble in the least possible quantity of 

 HC1, add lime water until just alkaline, boil, and filter. Raise 

 the clear filtrate to the boiling-point, and add pure ammonium 

 carbonate in excess. Allow to settle, wash thoroughly by 

 decantation, transfer to a platinum dish, and dry first in the 

 steam oven, then at a low temperature over an Argand burner. 



291. Preparation of Pure Ammoniutn Chloride. — The 

 great difficulty in performing the operation to be described 

 with commercial ammonium chloride is that the crystals are so 

 tough and wiry as to render powdering well nigh impossible. 

 This difficulty may be overcome by dissolving pure NH 4 C1 of 

 commerce in the smallest quantity of hot water, filtering, and 

 evaporating until the salt begins to crystallise. If it be now 

 cooled down rapidly by circulating cold water around the 



