A recent telegram from Nevada states that the Sutro Tunnel (of which I gave you some particulars in one of my letters) has now progressed a total distance of 15,565 feet and has fairly entered the mineral belt, and will soon help to increase the already vast products of the Comstock lode.
While on the subject of mining, I will state that the amount of quicksilver produced in California has increased so immensely during the last two years that it has attracted the attention of all interested in the article throughout the world. The receipts for the year have been 63,928 and the exports 48,010 flasks. In addition to the receipts there, probably about six thousand flasks were shipped direct from the mines to Nevada, thus bringing up the total production to over 70,000 flasks, a gain in round numbers of from twelve thousand to fifteen thousand flasks over 1875. The exports in that year were 34,844 flasks, or 13,666 less than in 1876.
Occasional.
Tyrian Purple Ink For Marking Linen.—Von Bele gives the following method for preparing an ink for marking linen and cotton: Neutralize 75 grains of carbonate of ammonia with pure nitric acid, and triturate 45 to 60 grains of carmine with the solution. Mordant the fabric with a mixed solution of acetate of alumina and tin salt, and write upon it, when it is perfectly dry, with the ink.
NEW YORK ACADEMY OF SCIENCES.
On Monday evening, January 29, 1877, a meeting of this Academy was held at the School of Mines, Columbia College, Dr. J.S. Newberry, President, in the chair. Mr. A.A. Julian, A.M., read a paper on the
PREPARATION OF ROCK AND MINERAL SECTIONS FOR MICROSCOPIC STUDY.
The speaker described in detail the various operations, exhibited the different kinds of apparatus employed, showed the operations, and exhibited the finished sections. In some rocks a thin chip can be broken off, others require to be sawn, and for the latter purpose the diamond saw is best. Having obtained the chip, it is first polished on one side, then cemented to a little square of glass, and the other side polished in the same way. The sections must not be too thick, nor too thin; they are usually made from a hundredth to a thousandth of an inch thick. Lathes employed in polishing minerals require to be provided with conical spindles, so that the wear, due to grit and emery dust getting on them, may be readily taken up. The grinding wheel may be either horizontal or vertical; the former has the advantage that the mineral can be held in either hand; with the latter only the right hand can be employed, and that in an awkward and tiresome position. Mr. Julian then referred briefly to the kinds of emery, its preparation by elutriation, etc., and cautioned operators against using rouge or tin putty powder in polishing rock sections, although they may be employed in polishing certain minerals and gems. The object of making the rock sections being to study their constituents and determine what minerals enter into their composition, it is important that no foreign substance, liable to adhere to the specimen and to be mistaken for one of its ingredients, be placed on the section while grinding. Lastly, the minerals are mounted on glass, with or without covers, by means of Canada balsam. Square glasses are to be preferred to the long and narrow strips, usually employed, as less liable to break in the center, and more easily revolved on the stage of a microscope.