Rock Section Catting Appavdtiis. 77 



One should not prepare too many lialsained slips at once, as 

 they continue to dry slowly if not used, and eventually become 

 too brittle. As to mounting, the specimen should be attached, 

 in the first instance, to the slip upon which it is to remain. 

 Transference to another slip is obsolete and unnecessary. It 

 did well for thick sections, which were formerly much more 

 common than they are, or should be, to-day. Again, the section 

 and slij) should not be flooded with ))alsam when about to 

 attach the cover, for, besides making a sticky and unsightly 

 mess, it is both wasteful and unnecessary. Prolojiged heating 

 of slip and section is not advisable, when one is mounting, with 

 the object of driving out all the solvent from the balsam. The 

 chances are, when this is attemijted. that the section will be 

 disturbed or float, and w^ill tend to break up when putting down 

 the cover, besides raising a crop of bubbles, which are very 

 difficult to remove. It is a. wiser and safer course to use no. 

 more balsam, and to apply no more heat than is necessary to 

 bring the cover into close and uniform relationship with the 

 whole of the section. An oven with a water jacket, main- 

 tained at about 40 deg. Cent., will, in from three to five clays, 

 complete the drying with perfect safety. 



So much for what is general and more or less applicable to 

 almost any successful process for the preparation and mounting 

 of rock sections. 



I will now briefly outline the process adopted with a col- 

 lection of, say, 20 numbered rock specimens, which are ready 

 for slicing. It is to be noted that I seldom prepare sections from 

 detached slices, as these involve two parallel cuts and much 

 subsequent grinding. It is twice as economical, both as to time 

 and material, to slice off the rock close to the mounting slip, as by 

 this method the smallest possible amount of material remains to 

 be ground away. Two dozen 3x1 inch slips are cleaned and 

 placed, the whole upon white blotting paper, spread on a sheet of 

 asbestos, or a metal plate ; this is laid upon a well filled sand 

 bath, supported on a tripod over a bunsen fiame. The heat 

 from the latter is so regulated as not to discolour or char the 

 paper below the slips. Each slip is now balsamed, using no 

 more than exi3erience has shown to be necessary for sections 

 about one inch in diameter. While the balsam is " cooking," 



