of water, and the wood is painted twice with this solution.  After five minutes the wood is washed, and grained with acetate of iron (the ordinary iron liquor of the dyer) at 20i Tw.  Dry, oil and polish as usual.  Gray—­1 oz. nitrate of silver is dissolved in 45 ozs. water, and the wood painted twice with the solution; afterwards the wood is submitted to the action of hydrochloric acid, and finally washed with ammonia.  It is then dried in a dark place, oiled and polished.  This is said to give remarkably good results on beech, pitch pine and poplar.  Black—­7 ozs. logwood are boiled with three pints of water, filtered, and the filtrate mixed with a solution containing 1 oz. of sulphate of copper (blue copperas).  The mixture is left to clear, and the clear liquor decanted while still hot.  The wood is placed in this liquor for twenty-four hours; it is then exposed to the air for twenty-four hours, and afterwards passed through a hot bath of nitrate of iron of 6i Tw.  If the black, after this treatment, should not be sufficiently developed, the wood has to be passed again through the first logwood bath.

The Highest Chimney in the World.—­The highest chimney in the world is said to be that recently completed at the lead mines in Mechernich.  It is 134 meters (439 ft. 6 in.) high, was commenced in 1884, and was carried up 23 meters before the frost set in; building was again resumed on the 14th of last April, and it was completed last September.  The foundation, which is of dressed stone, is square, measuring 11 meters (33 ft.) on each side, and is 3.50 meters (11 ft. 6 in.) deep; the base is also square, and is carried up 10 meters (33 ft.) above the ground.  The chimney-stack is of circular section, 7.50 meters (24 ft. 6 in.) diameter at the bottom, and tapering to 3.50 meters diameter (11 ft. 6 in.) at the top, and is 120.50 meters (395 ft.) high.

How to Measure Round Tanks.—­Square the diameter of the tank, and multiply by.7854, which gives the area; then multiply area by depth of tank, and the cubic contents will be found.  Allow 6-1/4 gallons for each cubic foot.

The Largest Buildings in the World.—­Where is the largest building in the world situated?  The answer to this question must depend upon what the term “building” is held to represent.  The Great Wall of China, 1,280 miles in length, wide enough to allow six horsemen to ride abreast along it, and with an average height of 20 ft., may fairly be called a building; so, too, may be called the Great Pyramid of Egypt.  The question, however, was not meant to include such works as these.  Some have supposed that the Vatican at Rome, with its eight grand staircases, 200 smaller staircases, 20 courts, and 11,000 apartments, is the largest building in the world; but surely this is a collection of palaces rather than a single building.  The same objection applies to the famous monastery of the Escurial in the province of Madrid, with its seven towers, fifteen gateways, and 12,000 windows and doors, and to many other vast piles.  For the largest single building extant, we must look to St. Peter’s at Rome, within which our great cathedral,