of delicate, fragile, lacy material or for microscopic organisms. Delicate residues 

 may be preserved by using very dilute hydrochloric acid, but the time required 

 for solution is lengthened. 



Beakers are the best receptacles for solution of the samples. They are pre- 

 ferred because the lip facilitates washing and decanting, residues may be easily 

 removed, and a glazed spot is provided on the side for identification of each 

 sample. Molded tumblers or other cheap glassware may be used, but the breakage 

 due to heat while drying samples equals or exceeds the greater original cost of 

 heat-resistant glassware. 



The procedure for residue preparation is simple. Samples of unit quantity 

 are placed in a glass receptacle properly identified on a slip of paper under a 

 pyrex dish or by any consistent regular arrangement. Samples are then digested 

 in acid, washed, dried, labelled, and stored for examination. The use of several 

 stainless-steel trays, or other type of tray holding 40 to 50 beakers, facilitates the 

 bulk movement of samples to the hood for acid application, washing, drying, or 

 other operations involving the handling of large numbers of samples. 



The first application of acid should be small to prevent foaming caused by 

 the rapid effervescence of powder and fine material. The foaming may easily 

 cause the overflow and loss of considerable material. A few minutes after the 

 initial application, additional acid may be added, but only experience will tell 

 how much, generally not more than one third to one half the capacity of the 

 receptacle. After several hours of digestion, the samples should be washed once 

 or twice to remove spent acid, precipitates, and undesirable material. The second 

 application of acid will generally complete the digestion, although one applica- 

 tion may be sufficient. Small applications of acid will digest samples which 

 obviously are chert, sand, or shale. Incomplete digestion will leave dolomite 

 pellets with rough, jagged surfaces and rounded pellets of limestone. When 

 samples are incompletely dissolved, individual euhedral dolomite rhombs may 

 be a large part of the residue. Final washing should be thorough to remove 

 all traces of acid and prevent scum, caking, or coating on the residues. 



Clay and fine silt are generally decanted in routine work. Little or no work 

 has been done with the fine residues, and their value for correlation and iden- 

 tification is yet to be determined. Perkins worked a year with the fines and 

 developed procedures to eliminate flocculation, but he found them too involved 

 and time-consuming for practical purposes. Petrographic study of the fines 

 require special equipment and give only academic results. He concluded, as 

 others have previously, that only the percentage and general physical properties 

 of the fines had any diagnostic value. Only outcrop or core samples can be used 

 for a study of the clay and silt residues, because caving and other contamination 

 of well samples obscure diagnostic features and make uncertain the identification 

 of indigenous fine clastic material. 



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