METHODS OF CLAY ANALYSES. 45 



METHODS EMPLOYED IN MAKING CLAY 

 ANALYSES.* 



The following brief statement of the methods em- 

 ployed in making the analyses of clays for this report 

 has been prepared by Dr. Charles Baskervilk, by 

 whom the analyses were made : 



Moisture Two grams are heated in a platinum 

 crucible at 100 C. until they show a constant weight. 

 The loss is reported as moisture. 



Loss on Ignition (combined water, and sometimes 

 organic matter, etc.) The crucible and clay are 

 heated with a blast lamp until there is no further loss 

 in weight. 



Alkalies This same portion of clay, which has 

 been used for determining moisture and loss, is treat- 

 ed with concentrated sulphuric and hydrofluoric acids 

 until it is completely decomposed. The acids are 

 evaporated off by heating upon the sand-bath. The 

 cooled crucible is washed out with boiling water to 

 which several drops of hydrochloric acid have been 

 added. The solution after being made up to about 

 five hundred cubic centimetres is boiled, one-half 

 gram ammonia oxalate added and made alkaline with 

 ammonium hydroxide ; the boiling is continued until 

 but a faint odor of ammonia remains. The precipitate 

 is allowed to settle and is separated from the liquid 

 by filtering and washed three (times with boiling 

 water. The filtrate is evaporated to dryness and ignit- 

 ed to drive off ammonia salts. The residue is treated 

 with five cubic centimetres of boiling water, two or 

 three cubic centimetres of saturated ammonium car- 

 bonate solution are added and the whole is filtered 



*Reprinted from Bulletin No. 13, North Carolina Geological Survey, 

 1897. 



