There are probably few of my readers who have ventured to trust themselves within a Nitro-Glycerin manufactory; the very name is sufficient to make the passer-by quicken his step, till he is a safe distance beyond the dreaded precinct. Some account of such a factory will, accordingly, be interesting to many who are familiar with the article, perhaps have used it, but whose curiosity has not been of such a nature as to induce them to pay a visit to the works, where the least negligence involves a death penalty. About 100 yards beyond the West shaft of the Hoosac Tunnel, is to be seen a board fence surrounding about ten acres of ground, with the announcement, “NITRO-GLYCERIN WORKS;—DANGEROUS;—NO VISITORS ADMITTED.” A drive leading between two rows of buildings brings the “visitor” to the acid house, a well-ventilated building, 150 feet long. Here are 11 stills, each seven feet long and two feet in diameter. Under these a light, slow fire burns, which is carefully attended to, for the temperature must be kept moderate. In each of these stills is placed 300 lbs. of nitrate of soda and 375 lbs. of sulphuric acid. A stoneware pipe conducts the gases, at a temperature of about 180°F, from each still into a stone receiver or condenser, or rather a series of four condensers connected by stoneware pipes, ranged on a platform three feet above the ground. Into the first of these 150 lbs. of sulphuric acid is poured, into the second 150 lbs., into the third 100 lbs., and the fourth is empty. The nitrous vapor passes from the still to the first condenser, where a portion of it, forming as it condenses nitric acid, is taken up by the sulphuric acid; the remainder passes on to the second, third and fourth condensers, though a very small portion is left to pass into the last, which only requires to be emptied once a month. It takes about twenty-four hours for the still to complete the conversion of its contents into nitric acid, at the end of which time the resultant mixture of acids, about 600 lbs., is run off into carboys, twelve of these being filled from three stills. About 100 carboys are generally kept in stock, as the acid does not spoil when kept closed. These carboys are then emptied into a soapstone tank having a capacity of 18 carboys, and an iron pipe, connected with the main leading from two blowers in the engine house, is inserted into the acid, causing a current of air to agitate it so as to remove the nitrous fumes, mix it thoroughly and bring it all to uniform strength. Formerly, this was effected by removing the acid into a glass vessel containing about forty gallons, and it required boiling for hours; the mode now practised occupies only five minutes and the risk of fracture of a glass vessel in a sand bath is avoided. The acid is then carried into the converting room, about one hundred feet long and well lighted, where it is weighed, seventeen pounds being poured into each