COLLECTING AND PREPARING, 815 



fossil with even greater detail than could be seen on the original 

 specimen. A small piece of gutta-percha is to be softened in hot 

 water and pressed into the moistened mold with the thumb, which 

 must be wet, to prevent sticking. Considerable pressure is 

 required, and the squeezed-out borders should be folded in again 

 in order to insure a perfect cast. "Pink gutta-percha (superior 

 quality) for base plates, "^^ gives the sharpest and best results. It is 

 however difficult to manipulate on account of its rapid hardening. 

 It comes in thin sheets of a pink color, but is rather expensive. 

 Another very good dental wax is the " yellow wax " manufactured 

 by the S. S. White Dental Manufacturing Co., 120 Boylston St., 

 Boston, Mass. It is pure bees wax prepared in thin sheets and 

 sells for 50 cents a half pound. It is softened by heating in hot 

 water. '' Modeling composition for dental purposes. No. 2, 

 medium," is often more serviceable than gutta-percha, because it 

 stays softer longer and is more easily manipulated; it is also 

 cheaper. Its deep red color makes it rather objectionable for 

 squeezes, and it does not take detail as readily as the gutta-percha. 

 It is likewise made soft by heating in hot water. It is obtainable in 

 half pound boxes from dental supply stores. 



To obtain the best results with the fossils of impure argillaceous 

 limestones, the following process, devised by J. M. Clarke, is 

 recommended : '' Let small fragments exposing fossils in section be 

 placed in dilute muriatic acid, until the calcareous matter is 

 removed to a sufficient depth from the surface to leave all im- 

 pressions of fossils at the surface perfectly clear. The argillaceous 

 or other impurity of the matrix left after the reaction will be 

 exceedingly soft, but retain the impressions, whether external or 

 internal, with exceeding delicacy of detail. The fragments may 

 then be carefully removed from the acid and washed, by placing 

 them for a moment in pure water. They should then be thor- 

 oughly dried, and afterwards hardened by cautiously soaking in a 

 very weak solution of glue, care being taken that this solution be 

 sufficiently thin to enter all the ornamental or structural cavities 

 and interstices of the impressions. After again drying, soft, clean, 

 and clear squeezes are to be taken with soft gutta-percha. To 

 preserve the hardened matrix, such squeezes must be taken rapidly, 



"Manufactured by Eugene Doherty, no and 112 Kent Ave., Brooklyn, N. Y. 



