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EECEEATIVE SCIENCES 



have been one of tlie first to prepare fossil 

 specimens of such wood (and coal) for the 

 microscope. This task is one of some dif- 

 ficulty and uncertainty. To succeed in it, 

 we must first grind a surface flat, and then 

 with lapidary's cement fix that surface to 

 a block of wood, by means of which the 

 fossil can be again ground down until con- 

 sidered thin enough. But then it is difficult 

 to detach the fossil from the block, and to 

 remove the cement without breaking it. 

 Mr. Nicol, however, adopted an easy and 

 simple process, which consisted in cement- 

 ing the flattened surface to a piece of plate- 

 glass, by means of Canada balsam, and then 

 grinding it down with emery on a plate of 

 copper. The glass and cement being both 

 transparent, the operator could determine 

 when he had arrived at the proper degree of 

 thinness ; and when that was attained, nothing 

 more was requisite than to polish the surface. 

 For a long time this method was compara- 

 tively secret, till Mr. Nicol wrote a full 

 account of all the requisite manipulations, at 

 Mr. "Witham's request, which was printed at 

 the end of that gentleman's work, entitled 

 " Observations on Fossil Vegetables," now 

 a scarce book. The manipulation, however, 

 in this kind of work is very delicate, and 

 demands considerable skill as well as pa- 

 tience, insomuch that we notice that Mr. 

 Sanderson's slices are prized to this day as 

 of great superiority. 



In pursuing the same object with re- 

 ference to coal, various methods of preparing 

 it may be adopted. Thin sections may be 

 obtained from those kinds which have suf- 

 ficient tenacity; but in proportion to the 

 opacity of the material must be its thin- 

 ness before it becomes transparent, and 

 in proportion to its thinness is its friability : 

 80 that just when we have brought it to the 

 necessary tenuity, it often crumbles and 

 disappoints our hopes. Skilful practitioners* 



* " Micrographic Dictionary." 



have found that if the coal is macerated, or 

 soaked to decay for about a week in a solu- 

 tion of carbonate of potass, it is possible at 

 the end of that time to cut rather thin slices 

 with a razor. These being placed in a watch- 

 glass, with strong nitric acid, covered, and 

 then gently heated, they soon become 

 brownish and then yellow ; when the process 

 must be arrested by dropping the whole into 

 a saucer of cold water, otherwise the coal 

 will be dissolved. Slices thus treated assume 

 a darkish amber colour, are very transparent, 

 and when a conspicuous structure is in the 

 original lump they exhibit it most clearly. 

 The specimens are best preserved, in glyce- 

 rine, in cells ; for the spirit renders them 

 opaque, and even Canada balsam has the 

 same effect. 



There are instances in which the coal is 

 so friable, that no sections can be made from 

 it by either of these methods. In such cases 

 it may be ground to fine powder, and the 

 particles, after being mounted in Canada bal- 

 sam, may be subjected to microscopic exami- 

 nation. It cannot be supposed that the re- 

 sult will be very satisfactory, but it may be 

 of considerable comparative value in relation 

 to other and more compact varieties. Even 

 the ash of ordinary coals (obtained by burn- 

 ing to white ash a specimen of coal previously 

 boiled in nitric acid, and then carefuUy 

 mounting the ash in Canada balsam) often 

 exhibits mineral casts of vegetable cells and 

 fibres. The ash of the Welsh anthracite is 

 useful for this purpose. It is necessary to 

 observe that the great bulk of the coals used 

 in our households, including all the coking 

 varieties, the anthracite, and the coals used 

 for steam-engines, are perfectly opaque, and 

 can only be viewed by reflected light. On the 

 other hand, the gas-coals (those employed 

 in gas-works), such as the Pelton gas-coals, 

 and those from Nova Scotia, together with 

 the cann el -coals, brown-coals, jets, and 

 lignites, can all be rendered more or less 

 transparent. Hence, however many varieties 



