The arrangement by which the reading rooms have been studiously kept in the rear of the building out of the reach of street disturbances, is one which gives it a great advantage over the public libraries of most other cities. There is a well furnished chess room for the lovers of that mental game, and conversation, waiting and other rooms requisite to perfectly complete a truly desirable city institution. We understand that the membership exceeds fifty thousand, and judging from what has been done, there is no reason to doubt its ultimately doubling that number in so large a city as this. * * * * * ARTIFICIAL STONE.—At the recent meeting of the Polytechnic Association of the American Institute, Mr. Thomas Hodgson exhibited and explained two methods of manufacturing and moulding artificial stone ornaments, blocks, etc., for buildings. One of these is prepared by treating lime with a solution of four ounces of oxalic acid in a gallon of water, thus producing an oxalate of lime, which is mixed with from two to four times its weight of sand. In this condition the material is a moist, friable powder. It is then moulded to the required form in Plaster-of-Paris moulds, removed from the latter, and suffered to dry. It is then preferably placed in a bath of dilute oxalic acid, which causes it to harden throughout, after which it is ready for use. In making the other variety, the inventor treats the oxalate of lime with a solution of silicate of potash, thus bringing it to a semi-fluid condition, whereupon it is poured into moulds and suffered to indurate. Dr. Van der Weyde said that the oxalate of lime, being one of the most insoluble substances known in chemistry, its employment in the fabrication of artificial stone was a lucky thought. The use of potash and soda compounds for such purposes had been extensively attempted with very poor results, but the oxalate of lime was free from objections which hold good against such compounds.—_Railroad and Mining Register._ * * * * *