208 PREPARATION OF OBJECTS. 



pentine for a while, to lay some liquid balsam upon the parts 

 through which the section is to pass, and then to place the speci- 

 men before the fire or in an oven for some little time, so as first to 

 cause the balsam to run in, and then to harden it; by this means 

 the specimen will be rendered much more fit for the processes it 

 has afterwards to undergo. It not unfrequently happens, that 

 the small size, awkward shape, or extreme hardness of the body, 

 occasions a difficulty in holding it either for cutting or grinding ; 

 in such a case, it is much better to attach it to the glass in the 

 first instance, by any side that happens to be flattest ; and then 

 to rub it down by means of the " hold" of the glass upon it, until 

 the projecting portion has been brought to a plane, and has been 

 prepared for permanent attachment to the glass. This is the 

 method which is generally most convenient to pursue with re- 

 gard to small bodies ; and there are many which can scarcely be 

 treated in any other way, than by attaching a number of them 

 to the glass at once, in such a manner as to make them mutually 

 support one another.' 



109. The mode in which the operation is then to be proceeded 

 with, depends upon whether the section is to be ultimately set 

 up in Canada balsam (§ 125), or is to be mounted dry (§ 122), or 

 in fluid (§ 132). In the former case, the following is the plan 

 to be pursued. The flattened surface is to be polished, by rub- 

 bing it with water on a " "Water-of-Ayr" stone, on a hone or 

 " Turkey" stone, or on a new stone recently introduced under 

 the name of the "Arkansas" stone; the first of the three is the 

 best for all ordinary purposes ; but the two latter, being much 

 harder, may be employed for substances which resist it.^ When 

 this has been sufficiently accomplished, the section is to be at- 

 tached with Canada balsam to a slip of thick, well-annealed glass; 

 and, as the success of the final result will often depend upon the 

 completeness of its adhesion to this, the means of most effec- 

 tually securing that adhesion will now be described in detail. 

 Some Canada balsam, previously rendered somewhat stiff" by the 

 evaporation of part of its turpentine, is to be melted on the glass 

 slip, so as to form a thick drop, covering a space somewhat larger 

 than the area of the section ; and it should then be set aside to 

 cool, during which process, the bubbles that may have formed in 

 it will usually burst. "When cold, its hardness should be tested, 

 which is best done by the edge of the thumb-nail ; for it should 

 be with difficulty indented by its pressure, and yet should not be 



' Thus, in making horizontal and vertical sections of Foraminifera, as it would be im- 

 possible to cut them through, they must be laid close together in a bed of hardened 

 Canada balsam on a slip of glass, in such positions, that, when rubbed down, the plane 

 of section shall traverse them in the desired directions; and one flat surface having 

 been thus obtained for each, this must be turned downwards, and the other side ground 

 away. 



' As the flatness of the polished surface is a matter of the first importance, that of the 

 stones themselves should be tested from time to time ; and whenever they are found 

 to have been rubbed down on any one part more than on another, they should be flat- 

 tened on a paving-stone with fine sand, or on the lead-plate with emery. 



