There is in use among railroads and such companies a kind of pipe which is especially fitted for their purposes. It is called among manufacturers the Cincinnati Standard, and the point of difference between it and the ordinary pipe in the market is in the thickness of the shell, making a 24- pipe 2 inches thick instead of 1 inches, as usual. The gang necessary to run a press are : 1st, one man to fill the mud-cylinder ; 2d, one en gineer; 3d, one man to cut the pipe and help handle the pipe ; 4th, one man to manipulate the socket shaper ; 5th, from one to three men to carry off the pipe. At one of the Eliottsville works, a press is in use having two mud-drums parallel, which are filled and pressed alternately, so that the press may work constantly instead of filling, pressing, and waiting to refill. The drums are shifted backward and forward by a horizontal cylinder to one side. The capacity of a press varies with the kind of clay used, the size of pipe made, and many other con .
ditions, but in normal working, will not vary far from these figures ; 36-inch press, making 6-inch pipe, 3,00o feet a day ; 12-inch pipe, 1,000 feet daily ; 15-inch pipe, 80o feet ; 18-inch pipe, 65o feet ; 2o-inch and 24-inch pipe, about 500 feet daily.
The heat used in sewer-pipe burning is only that necessary to get a good salt glaze ; about one barrel of salt to a kiln is required. Coal is the fuel invariably used.
The process of glazing with salt is of ancient origin, and it consists in throwing the salt into the kiln towards the end of the firing, and just before the highest heat is obtained.
Salt that has been used for pickling can be employed, as it is not requisite that it should be pure.
The fires should be properly managed, and at the right tem perature, in a closed kiln or oven ; the salt is thrown uniformly through the holes at the top of the kiln. Small, light scoop shovels are best for this purpose. The quantity of salt neces sary for a moderate-sized oven is 150 to 160 pounds. About one-half the quantity of salt having been thrown into the oven, the fire is momentarily increased, then reduced, and a few specimens of clay burned with the pipes are examined, for the purpose of testing the glaze. The remainder of the salt is then thrown in, part at the top of the kiln, and part regularly over the top of the fire.
The temperature of the kiln is so high at the " burning off," or end of the firing, that the volatile salt is at once converted into vapor, which intimately surrounds the pipes in the kiln, and there is consequently a reaction of the vapor on the silica of the clay bodies.
The agent which promotes the reaction of the silica and com mon salt is the aqueous vapor which is always present in the flames of the furnace. The oxygen of the water produces soda with the sodium of the common salt, while the hydrogen com bines with the chlorine, and is evolved as hydrochloric acid. The soda then enters into combination with the silica and forms the glaze.
The glaze produced upon the earthenware pipes in the man ner described is consequently a soda-glass, and forms a very thin film or coating upon the material. It is of course manifest that the greater the quantity of silica a clay contains the more readily will it decompose salt, and the more lustrous will be the glaze produced. When it is desired to secure the brown color so common on drain-pipes, it is communicated to the glaze by throwing such substances as birch bark into the fire during the glazing process, and the larger volume of smoke thus evolved produces the desired effect. It sometimes happens that the
ware in some portions of the kiln becomes covered with salt, a part of which then appears as an efflorescence.
After the kiln has been properly fired all the doors and open ings are carefully daubed around with a mixture of sand and clay, a few air-holes in the furnace-doors not exposed to the wind being allowed to go unplugged for a few hours, and after two or three days the burned and vitrified sewer-pipe is ready to be removed and shipped to market.
The finished sewer-pipe are stacked up in piles ready for sale. The fittings which go with the pipe, such as curves, elbows, Straps, 1-pieces, X, Y and U-pieces, etc., are made for the different sizes of pipes ; they are separately moulded and are more expensive than the lengths of pipe, as they are made mostly by hand in plaster molds, and all the other special shapes. The " river pipe " manufactured in Ohio are made from a homogeneous clay ; i. e., the clay by the nature of the preparatory steps, is reduced to a fine, even state of division, and by the character of the tempering plant is made into a perfectly uniform paste. And as it enters the pressing chamber in a comparatively fine state, the force which com presses it does not make the lines of demarkation between the particles which composed the mass apparent, as it would if the clay were not as soft as it is, and as finely divided. So when a piece of river pipe is broken its fracture shows an even, fine grained structure, not so fine as stone-ware, but very similar and varying from a buff to a grayish-blue. This latter is the best tint to get, as it insures the combination of whatever im purity the clay contains with the free sand, and development of the best qualities of the clay. The use of salt makes the color a necessity, as a rule, for the combination of iron always begins before the glazing by salt vapor does. The strength that these pipe have is far in advance of any other Ohio pipe, as the structure, seen on the fracture, would show. The degree of heat which the clay will stand without injurious effects is far above the glazing heat of the pipe, and the only precaution in the burning to be observed is to secure enough heat with no close limit on the side of excess. The iron found in these Kit tanning clays is present in small grains, which, under the action of the salt glaze, make unsightly black blisters and holes in the surface, though in no degree injuring the utility of the ware. This feature has hitherto much injured its popularity. It is beginning to receive more credit than ever before, because its superior strength and durability are now being recognized. The color of the river pipe is light-red ; in spots, where the heat did not get access to it, it is light buff, and in over-burnt portions a dark-red color, which has not a pleasing effect. The even, beautiful red color of the Akron and Columbus pipe have been the secrets which have given them their popularity above other kinds, but experience teaches that the color is not essential to the best results. The river pipe, on account of their light, red color, and mottled, spotted appearance, have not had popularity in the West, particularly in Chicago, the greatest of all markets, but they are constantly gaining ground there.