158 THE POPULAR SCIENCE MONTHLY. 



arsenious acid, or nitrate of soda is used to make the glass color- 

 less. 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 Glass- 

 boro the mixing as well as the grinding will soon be done by ma- 

 chinery 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 develop- 

 ment of the bottle is to change this dull-white powder into clear, 

 fluid glass. Such a metamorphosis is accomplished in the melt- 

 ing 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 em- 

 ployment of a tank in place of separate crucibles, nor the substi- 

 tution of a gaseous for a solid fuel, is in itself new ; but the details 

 of the Ferrari furnace are quite novel. In Europe, the regenera- 

 tive system of Siemens has been employed with marked success 

 in the manufacture of glass ; but, unfortunately, the Siemens fur- 

 naces are expensive in their construction and require some de- 

 gree 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 neces- 

 sity 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 com- 

 pletely burned that is to say, it unites with all the oxygen possi- 

 ble, forming carbonic-acid gas. The supply of air may be regulated 



