. Bulletin - United States National Museum. Science. Fig. 10.—Balsam bottle. is referred to any authoritative work on tlie subject of liglit, and to Prof. J. P. Idding's translation of Professor Eosenbuscli's work on optical mineralogy. ^ But to return to the subject of making sections. A thin chip of the size of a nickel 5-cent piece, or at most not over an inch in diameter and as thin as j)ossible, is broken from that portion of the rock selected for study. By means of emery and water on a smooth cast-iron plate, one side is then ground until all inequalities are obliterated. The final grind
. Bulletin - United States National Museum. Science. Fig. 10.—Balsam bottle. is referred to any authoritative work on tlie subject of liglit, and to Prof. J. P. Idding's translation of Professor Eosenbuscli's work on optical mineralogy. ^ But to return to the subject of making sections. A thin chip of the size of a nickel 5-cent piece, or at most not over an inch in diameter and as thin as j)ossible, is broken from that portion of the rock selected for study. By means of emery and water on a smooth cast-iron plate, one side is then ground until all inequalities are obliterated. The final grinding must be done with emery so fine as to leave no per- ceptible scratches. This chip is then cemented, smooth side down, against a small piece of ordinary double-thick window glass, by means of Canada balsam, such as may be procured at almost any drug store, and which, in its liquid form, is best kept in a capped bottle as shown in fig. 10.^ The glass serves merely as a holder and may be of any convenient size. Eectangular pieces one by two inches have been found most convenient in this labora- tory. In cementing the chip a few drops of the liquid balsam are placed upon the center of the glass slip, which is then gently heated until such quan- tity of the volatile constituents pass olf that on cooling the residue is hard but not brittle. Experience is here the only guide; if heated too long it will become brittle and break away; if not long enough it is soft and sticky. Hard enough to be impressed slightly by the thumb nail without sticking or cracking is as definite as can be well stated. In case a large number of sections are to be prepared it is well iMicroscopic Physiography of Eock-Making Minerals. Wiley & Sons, New York. 2 Some workers profess to prefer a mixture of Tsnetian turpentine and white shel- lac boiled down to proper consistency. Fig. 11. Fig. 12. Mounting needle and Please note that these images are extracted from scanned page images that may h
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Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
