508 PKEPAKATION, MOUNTING, AND COLLECTION OF OBJECTS 



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. 1 



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, or is to be mounted ' dry,' or in fluid. In the former case 

 the following is the plan to be pursued : The flattened surface is to 

 be polished by rubbing it with water on a ' Water-of-Ayr ' stone, or 

 on a hone or ' Turkey ' stone, or on an ' 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. 2 

 When this has been sufficiently accomplished, the section is to be 

 attached with hard 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 effectually 

 securing that adhesion will now be described in detail. The slide 

 having been placed on the cover of the water-bath, and the previously 

 hardened balsam having been softened by the immersion of the jar 

 containing it in the bath itself, a sufficient quantity of this should be 

 laid on the slide to form, when spread out by liquefaction, a thick 

 drop, somewhat larger than the surface of the object to be attached. 

 The slide should then be allowed to cool in order that the hardness 

 of the balsam should be tested. If too soft, as indicated by its 

 ready yielding to the thumbnail, it should be heated a little more, 

 care being taken not to make it boil so as to form bubbles ; if too 

 hard, which will be shown by its chipping, it should be remelted 

 and diluted with more fluid balsam, and then set aside to cool as 

 before. When it is found to be of the right consistence, the section 

 should be laid upon its surface with the polished side downwards ; 

 the slip of glass is next to be gradually warmed until the balsam is 

 softened, special care being taken to avoid the formation of bubbles ; 

 and the section is then to be gently pressed down upon the liquefied 

 balsam, the pressure being at first applied rather on one side than 

 over its whole area, so as to drive the superfluous balsam in a sort 

 of wave towards the other side, and an equable pressure being finally 



1 Thus, in making horizontal and vertical sections of Foraminifera, as it would 

 be impossible to slice 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. The following ingenious plan was suggested by Dr. Wallich (Ann. 

 of Nat. Hist. July 1861, p. 58) for turning a number of minute objects together, and 

 thus avoiding the tediousness and difficulty of turning each one separately : The 

 specimens are cemented with Canada balsam, in the first instance, to a thin film of 

 mica, which is then attached to a glass slide by the same means ; when they have 

 been ground down as far as may be desired, the slide is gradually heated just suffi- 

 ciently to allow of the detachment of the mica film and the specimens it carries ; and 

 a clean slide with a thin layer of hardened balsam having been prepared, the mica 

 film is transferred to it with the ground surface downwards. When its adhesion is 

 complete, the grinding may be proceeded with ; and as the mica film will yield to the 

 stone without the least difficulty, the specimens, now reversed in position, may be 

 reduced to requisite thinness. 



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



