708 SUMMARY OF CURRENT RESEARCHES RELATING TO 



On*' should not prepare too many balsamed slips at once, as they 

 continue to dry slowly if not used, and eventually become too brittle. A- 

 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 slip should not be flooded with balsam when about to 

 attach the cover, for, besides making a sticky and unsightly mess, it is 

 both wasteful and unnecessary. Prolonged 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 attempted, 

 that the section will be disturbed or float, and will 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, maintained at about 40° C, will, in from three to five 

 days, 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 collection of, 

 say. twenty 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 3 by 1 in. 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 flame. 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 experience has shown to 

 be necessary for sections about 1 in. in diameter. While the balsam is 

 " cooking " the specimens are successively clamped in the large specimen 

 holder of the slicing machine, and a piece, large enough for a section, is 

 sliced away ; the whole twenty being thus treated. Meantime, the bal- 

 samed slips will have become sufficiently hardened. Each slip should be 

 separately tested, when cool, with forceps or knife ; the hardened balsam 

 should indent with moderate pressure without splintering. 



The sliced face of each specimen is now, for a few seconds, held upon 

 the finest revolving lap. which is fed with F F carborundum, and moist- 

 ened with water containing about one-fifth of its volume of glycerin, 

 which maintains a rapidly revolving disc sufficiently moist, without ex- 

 cess, for a long time. Each specimen requires only a brief treatment, 

 and if the lap is in first-class order no further preparation should be 

 required. Usually, however, it is safer to give each specimen a few 

 sweeps by hand, upon a slate or glass lap, the surface of which should be 

 accurately true or 'flat. After washing and drying, the specimens are 

 ready for attachment to the balsamed slips. This is done by heating 

 them sufficiently to occasion discomfort when held against the hand for 



