116 CHAPTER IX. 



dehydrated with alcohol. A thin solution of copal in chloro- 

 form is prepared by triturating small fragments of copal in a 

 mortar with fine sand, pouring on chloroform to the powder 

 thus obtained and filtering. The objects are brought into 

 a capsule filled with the copal solution. The solution is now 

 slowly evaporated by gently heating the capsule on a tile by 

 means of a common night-light placed beneath it. As soon 

 as the solution is so far concentrated as to draw out into 

 threads that are brittle after cooling,, the objects are removed 

 from the capsule and placed to dry for a few days on the tile 

 in order that they may more quickly become hard. When 

 they have attained such a degree of hardness that they cannot 

 be indented by a finger-nail, sections are cut from them by 

 means of a fine saw. The sections are rubbed down even 

 and smooth on one side with a hone, and cemented, with this 

 side downwards, to a slide, by means either of Canada balsam 

 or copal solution. The slide is put away for a few days more 

 on the warmed tile. As soon as the cement is perfectly hard 

 the sections are rubbed down on a grindstone, and then on a 

 hone, to the requisite thinness and polish, washed with water, 

 and mounted in balsam. 



The process may be varied by imbedding the objects 

 unstained, removing the copal from the sections by soaking 

 in chloroform, decalcifying them if necessary, and then 

 staining. 



It is sometimes a good plan, after removing the copal, to 

 cement a section to a slide by means of hard Canada balsam, 

 then decalcify cautiously the exposed half of the specimen, 

 wash, and stain it. 



This method was invented in order to enable the hard and 

 soft parts of corals to be studied in their natural relations, 

 and is valuable for this and similar purposes. 



178. EHREKBAUM'S Colophonium and Wax Method (Zeit. ici>s. 

 MiJc.j 1884, p. 414).--Ehrenbaum recommends a mass con- 

 sisting of ten parts of colophonium to one of wax. The 

 addition of wax makes the mass less brittle. Sections are 

 obtained by grinding in the usual way. The mass is removed 

 from them by means of turpentine followed by chloroform. 



179. JOHNSTON E-LAVIS and VOSMAEK'S Balsam Method (Joiirn. 



8oc. f 1887, p. 200). Alcohol material is carefully 



