BULLETIN 39, UNITED STATES NATIONAL MUSEUM. 



[26] 



will also assist in removing the acid. After the material has dried, sift 

 it through the three sieves described under "Clay and marl washing." 



Phosphatic shells, such as thick-shelled or very small linguloids or 

 graptolites of a half-carbonized, chitinous substance, can also be etched 

 out of limestone, but here the acid solution must be very weak. Final 

 or delicate etching can be done with vinegar more or less diluted. 



Siliceous fossils from red soils can be bleached with oxalic acid dis- 

 solved in water, to which action subject them for a day or twoj then 

 soak them in water for a few days more, changing frequently to get rid 

 of all acid. 



To remove hard clay from the calyxes of corals or the interior of 



Fig. 8. 





lM 



PlO. 9. 



Tig. 10. 



Pig. 11. 



Fig. 12, 



Cutting tools. 



shells and other objects, caustic potash is often very serviceable. Fos- 

 sils cleaned in this way, however, must be solid and.without cracks, for 

 the potash will penetrate into the minutest fracture and force the parts 

 asuuder. " Caustic potassa" comes in round, slender sticks sealed in 

 one-half and one-i30und bottles. Keep the potash sealed in the bottles 

 with paraffin and cork stoppers. Handle the pieces with iron forceps^ 

 not with the fingers. In cleaning fossils have the parts to be acted on 

 uppermost, and on these lay small pieces of solid caustic potash. After 

 the potash has acted for a day or so wash the dirt away which rises in 

 puffed masses, and continue the application of fresh potash until the 

 parts are cleaned. To get rid of all potash, which if not removed will 

 for years after come to the surface in a white film, soak the fossils in 



