felspathic minerals, which generally also contain considerable proportions of iron. The use of these minerals also introduces notable proportions of alumina into the glass. In certain classes of bottles, notably those used for special wines, certain shades of colour are required--the well-known “Hock bottle” colour being an example. The presence of iron in the glass tends to the production of a green or greenish-yellow colour deepening to a black opacity if the quantity of iron be high. The lighter shades of this green tint may be “neutralised” by the introduction of manganese into the glass, the resulting colours ranging from light amber to purple; nickel oxide is also sometimes used as a colouring material in these glasses. In the production of ordinary bottles the continuous tank furnace has now entirely superseded the old pot furnaces, the character of the product being in this case particularly suited to this process of production. The modern bottle-glass tank is generally an oblong basin having one semi-circular end. The flame is often of the “horse-shoe” type, the gases both entering and leaving the furnace at the flat or charging end of the furnace. The raw materials are thrown into the furnace at the square end of the tank, and the glass flows uninterruptedly down the furnace to the colder semi-circular end where the working holes are situated. At these points fire-clay rings are kept floating on the glass, and from within these the gatherer takes his gathering, the rings serving to retain the grosser impurities carried down by the glass. The producing power of such a furnace, even when the bottles are blown by hand, is very considerable; a furnace having ten working holes and containing normally about 85 tons of molten glass will yield some four million bottles per annum, and furnaces of considerably larger capacity are in use. The methods of bottle making are at the present time passing through what is probably a stage of transition. Up to the middle of last century the processes in use were little better than those of the middle ages; the first step of a more modern development of the industry took the direction of improved tools and implements for carrying out the old operations. More recently a whole series of inventions have been put forward with the aim of producing bottles by entirely different and wholly mechanical processes with the object of eliminating the uncertain element of skilled labour entirely. While it must be admitted that some of the earlier of these inventions proved to be brilliantly ingenious failures, there is little doubt that here, as in other manufacturing processes, the machine-made article will ultimately supersede the hand-made product. Even now, mechanical processes are largely in use both in America and Europe, and at some recent exhibitions machine-made bottles have been shown which in every point of quality were superior to the best hand-made goods.