Page:Popular Science Monthly Volume 36.djvu/170

158 arsenious acid, or nitrate of soda is used to make the glass colorless. Blue bottles are occasionally wanted, and in that case a little peroxide of cobalt is added to the customary batch to give the required color.

To obtain the best results, it is essential that the grinding and mixing of the crude materials be carefully looked after. At Glassboro the mixing as well as the grinding will soon be done by machinery in one central mixing-room, and the batch conveyed to the different furnaces by means of endless belts. It is believed that this improvement will insure a better product as well as more economical working.

The batch having been prepared, the next step in the development of the bottle is to change this dull-white powder into clear, fluid glass. Such a metamorphosis is accomplished in the melting furnace, which forms very naturally the central feature in a bottle-factory. The gratifying increase in the capacity of the Glassboro works is largely if not entirely due to the introduction of improved furnaces invented by the chemist of the works, Mr. Andrew Ferrari. They are continuous tank furnaces heated by gas—that is to say, the melting is carried out in large fire-clay tanks, and proceeds without interruption. There are other tank furnaces in use in America, but these are probably the only works where the melting is carried out continuously. Neither the employment of a tank in place of separate crucibles, nor the substitution of a gaseous for a solid fuel, is in itself new; but the details of the Ferrari furnace are quite novel. In Europe, the regenerative system of Siemens has been employed with marked success in the manufacture of glass; but, unfortunately, the Siemens furnaces are expensive in their construction and require some degree of skill to insure their best working. The Ferrari furnace, on the other hand, is an inexpensive affair and is easily worked. The gas generator is the usual inclined or "step" grate employed by Siemens, but it is placed directly alongside of the furnace, thus obviating the transportation of the gas, and the consequent necessity of reheating it before combustion.

At one end of the building one sees an elevated platform on which are stacked large blocks of bituminous coal. About six tons are daily required for each furnace. From this platform a line of low, irregular brick-work extends to the central stack. It contains the gas generators, three to each furnace, and beyond them the melting tank, which communicates on the other side with what is known as the working part of the furnace, lying directly under the central stack. The coal is fed directly into the generators from the platform, and on the inclined grate is completely burned—that is to say, it unites with all the oxygen possible, forming carbonic-acid gas. The supply of air may be regulated