ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 921 



point of a knife, and a drop of the acid, wliicli is to be applied, placed 

 on it. In tlie application of hydrocbloric acid Wichmann allows it 

 to dry, redissolves in another drop, and brings the solution by means 

 of a capillary pipette or platinum sjjatula to a part of the slide away 

 from the region of the section. If one is dealing with fluo-silicic 

 acid, the drop is removed with a jilatiuum spatula as soon as it has 

 half di'ied. In this case it is judicious to hasten the decomposition 

 by previously adding a drop of watery fluoric acid. 



For dealing with isolated particles of a mineral in a powder, it is 

 best to cover a carefully cleaned slide with the balsam in ether, and 

 before it has dried sprinkle a small quantity of the powder on it, so 

 that the particles adhere to it. The balsam is allowed to dry, and 

 one then searches for the granules of the mineral under the Micro- 

 scope, and covers over all the others with more balsam solution. The 

 granules thus isolated can be treated in the usual way. 



Isolating Minerals in Sections for Micro-chemical Examina- 

 tion.* — Dr. A, Strong uses cover-glasses which are prepared by dipping 

 them into melted wax, and, when this is cold, making an opening 

 (1/2-1 mm,) with a pin in the middle of the wax. The spot so laid 

 bare is covered with a drop of concentrated hydrofluoric acid, until 

 it is perforated, and the remaining wax is then removed. To examine 

 a given mineral chemically, one side of the perforated cover-glass is 

 covered round the opening with a thin layer of heated Canada balsam, 

 and this side is, when the balsam has set, laid on the section in such 

 a way that the opening is over the mineral to be tested. By means 

 of a heated wire the balsam is melted. The opening thus filled with 

 balsam is made free by a brush dij)ped in alcohol, and test solutions 

 can be applied to the mineral. By warming the slide, the cover-glass 

 can be lifted off, and the various reactions studied on it. 



The Microscope in Geology.f — Mr. G. H. Williams, in an article 

 on this subject, recurs to what we have before commented on, viz. the 

 comparatively limited appreciation among Englishmen of the micro- 

 scopic study of rock-sections. Ho refers to what he terms the " sur- 

 prising fact that the appreciation of it among English-speaking people 

 has been so slow, that not one reliable text-book on the subject of 

 petrography exists in the language of the man who gave the first 

 impulse to its modern development," forgetting, however, Mr. Rutlcy's 

 ' Study of Rocks.' 



He also points out that " heretofore microscopical petrography has 

 been essentially a branch of mineralogy, but its future certainly lies 

 in the far wider sphere of geology. The mere laboratory study of 

 isolated rock specimens, which has served so good a purpose in the 

 perfecting of delicate and accurate methods, no longer jiosscsscs any 

 significance, now that these arc so tlioroughly developed. What in 

 Germany has been secured by years of patient labour may now be 

 learned in a comparatively short time. Geologists have only to know 

 and realize its application to their field of work in order to eagerly 



• Bcr. OborhcBB. Goscll. f. Naliu-. u. Iloilk., xxii. (1883) i>. 2G(). 

 t Science, v. (1885) pp. 190-1. 



