ANATOMICAL TECHNIQUE 461 



METHODS OF SECTIONING COAL 



This mineral is now universally recognized to be of vegetable 

 origin. Its practical importance and the interesting remains 

 which it contains make it an object not without interest both from 

 the general botanical and from the anatomical standpoints. All 

 except the most highly carbonized coals may be prepared for 

 sectioning on the microtome without great difficulty in accord- 

 ance with the summary method here described. The mineral is 

 split in conformity to the layers by means of a stout knife and a 

 hammer. The thin slabs thus secured are broken transversely 

 by the aid of pliers or a chisel into pieces which vary in size accord- 

 ing to the resistance of the coal. The fragments are put into 

 melted phenol or carbolic acid and kept in corked bottles in the 

 warm bath for about a week. They are then transferred after 

 washing in warm water to strong hydrofluoric acid for a second 

 week. Except in the case of certain lignitic coals further treat- 

 ment with phenol after washing with water is necessary. This 

 is followed by a second immersion in hydrofluoric acid and subse- 

 quent washing. After a third return to phenol (if this is necessary) 

 the material is washed in water and then run up into absolute 

 alcohol which must be changed two or three times. During the 

 process of dehydration the coal is kept in or on the paraffin bath. 

 Imbedding in nitrocellulose follows. In this process only 2, 4, 

 and 6 per cent solutions of celloidin are used, and the last of these 

 is followed at once by nitrocellulose of 16 per cent strength. It 

 is an advantage in imbedding coal, not only to pump all air out of 

 its substance, but also, when in the 6 per cent celloidin, to subject 

 to a positive pressure of between two and three hundred pounds. 

 This is easily effected by inclosing in a metal cylinder and raising 

 the internal pressure by means of an automobile pump. After a 

 rapid course of thickening rendered possible by the resistant char- 

 acter of the material, the pieces are dropped into chloroform in the 

 usual manner and later transferred to glycerin and strong alcohol. 

 In sectioning, the fragments of coal are clamped securely in the 

 wood-carrier of the microtome and cut with a transversely placed 

 knife. Only sections which are five micra or less in thickness are 

 of value in the case of this extremely opaque material. The 



