PROSPECTING AND EXPLOITING 143 



for a short fcime, and then treated in the same way as when 

 manganese was absent, for the determination of lime and mag- 

 nesia. 



For the determination of alkalies one grain of clay is mixed by 

 grinding in an agate mortar with one grain of granular 

 ammonium chloride and eight grains of pure calcium carbonate, 

 the mixture transferred to a platinum crucible with a well-fitting 

 lid and slowly heated to decompose the ammonium chloride, 

 theo heated to redness and the bottom of the crucible kept 

 at a bright red for about an hour. The contents of the crucible 

 are transferred to a porcelain casserole with about 80cc. of water 

 and heated to boiling ; this is then filtered and to the filtrate 

 after evaporation to small bulk about one and one half grams 

 pure ammonium carbonate added and the solution heated nearly 

 to boiling and filtered into a platinum dish, evaporated nearly 

 to dryness, a little more ammonium carbonate added and the 

 evaporation finished on the water bath. If the last addition of 

 ammonium carbonate produced a precipitate the residue in the 

 dish is dissolved in a little water and filtered into another 

 platinum dish where it is evaporated into dryness and ammonia 

 salts driven out by heat. The residue is dissolved in water 

 filtered into a weighed platinum dish, evaporated, dried and 

 weighed as Ka CI + K CI. If the last addition of ammonium 

 carbonate failed to produce a precipitate the transfer to another 

 dish ma} be dispensed with and the ammonia salts driven off at 

 once. 



Prospecting and exploiting 



In prospecting for clay the topography is often of much help. 

 In the northern and western portions of the state the clay is gen- 

 erally found in the bottoms of broad valleys. An example of this 

 is the Genesee Valley. Again at other localities the clay is 

 found underlying terraces along the sides of the valleys as in the 

 Hudson valley and along Lake Champlain. Deposits of a similar 

 character Avill be found along the Delaware and Susquehanna 

 Rivers. A terrace however does not necessarily indicate the 

 presence of clay, for some of the Hudson valley terraces are 

 underlain by till. 



