[11] 



DIRECTIONS FOR COLLECTING ROCKS MERRILL. 



emery. It is not necessary that tlie section be polished, as the balsam 

 in which it is mounted will correct all inequalities and bring about the 

 same results. When of the xjroper thinness — and there is no definite 

 rule — say from -^^^ to g^o inch, it is washed in alcohol or spirits of tur- 

 pentine to remove all the old balsam and included dirt, as well as such 

 particles of the emery as may have become embedded in the section. 

 This may be done with an ordinary toothbrush and in running water. 

 If the chip is properly secured to the glass there is no fear of injuring 

 it in this work, but it may be brushed over vigorously. 



This done, the slip for the final mounting is placed upon the iron 

 plate, not too hot, and the cleaned section still on the thick glass 

 beside it. A drop of liquid balsam is then put both upon the center of 

 the fresh slip and upon the section. Both are allowed to become suffi- 

 ciently warm to spread out well, but not enough to become, on cooling, 

 so hard as in the first process. A thin cover glass is then laid over the 

 section and iDressed down in place as though for a j)ermanent mount. 

 Then taking this slip with the section, by means of forceps, in the left 

 hand, bring it directly over 

 the clean mounting slip, 

 and by means of a needle 

 point in the right hand 

 push the ground section 

 and its cover glass with it 

 off into the balsam on the 

 new slide, in such a way 

 as to exclude air bubbles. 

 The object of first putting 

 the cover on the section is 

 merely to give it support in 

 process of transfer. Otherwise it is liable to become broken. Many 

 rocks, such as sand and limestones, are so friable that in the form of 

 thin films they can not be transferred at all, but must be mounted for 

 grinding on the thin glass on which they are to remain and afterwards 

 covered without removal. In such cases the cover glasses are best 

 cemented on by means of a solution of hard balsam in ether or chloro- 

 form. Since in the work of grinding the slide becomes badly scratched 

 and otherwise defaced, it is well, for appearance's sake, to grind the 

 entire surface of the slide before mounting. The index of refraction of 

 the balsam is such as to correct all inequalities in the glass and the 

 resultant slide is very pretty. In case a rock is so friable as to prevent 

 the production of the smooth surface so essential, it can be indurated 

 by boiling in balsam until the latter has so permeated all the pores as 

 to act, on cooling, as a cement. Slides made from such chips can not 

 be transferred, as a matter of course. 



In the final mounting some care is also necessary in evaporating the 

 balsam to just the right consistency. If left too soft it will continue to 



_f'iG. 14. — Grinding plate. 



