The grinding takes from forty-five to fifty minutes, and about 1,200 pounds constitute a charge ; the water used is added by the bucketful, and the clay is tempered very stiff. In many works they use only two-thirds as many machines as necessary, and run part of their plant all night to get the necessary clay for the next day's campaign. The ground clay is shoveled into a squeezer either of the screw or piston type, and it is concen trated into a long compact cylinder about 6 inches or 8 inches in diameter. This is cut up in lengths of about 15 pounds weight, and is fed to the machine in that shape. From this results the worst trouble of the Akron pipe ; the stiffness of the clay and the large, well-compressed wads in which it is fed, act together in keeping the clay from uniting to a homogene ous mass. Even under the powerful pressure of the machine, the lines of demarkation between the different pieces going to make up a pipe are plainly to be seen on the fracture of a burned pipe. They are arranged in circles concentric to the outside of the pipe, and often a crack of one-sixteenth of an inch separates the layers of the clay. This is all developed on burning, but is not visible before to any such degree. The working of the clay is admirable. It issues from the press as smooth as if moulded with oil, and the sockets are beautifully true and correct. The drying, setting and burning need no special attention. The kilns used are the same as are used for burning stone-ware ; they are oblong, end-fired down-drafts, about 3o to 35 feet long, and 15 to 20 feet wide, with an ave rage capacity of about 40 tons. The burning takes six days.
The character of Akron sewer-pipe-ware has already been hinted at in the description of the river pipe. It is a smooth, handsome ware, well-shaped, of a beautiful dark red-brown color, and remarkably uniform. On its fracture it shows the red color of a brick or even a darker red, which demonstrates the presence of iron in that peculiar state so hard to define, which is necessary to the development of the high color ; the per cent. of iron must be high, yet but little of that offensive blotch ing seen on the river-made ware can Be noticed. The weaken ing of the whole structure by the concentric cracks due to the pressing is the worst fault of the pipe.
As to the inability of the Akron works to make the Cincin nati Standard pipe, this is to be said : The increase of thickness of their pipe, with the same amount of drying which they now give it, is liable to cause large flakes to spall off from the sides of the pipe when heated in the kiln. With a longer and hotter drying they could make these thick pipe, but as their capacity is used to the fullest rate now, they are under no necessity to begin its manufacture. One point where they hold a decided advantage over the river district, is the use of the patent device for making curves, elbows, S's and traps. They can control the position of the core inside the mud-drums by a lever, and by moving it so as to make one aperture smaller than the other, the clay issues the fastest on the thinnest side and the pipe takes a curve shape. Also by using a softer clay on one side than the other, the softest part issues faster and the pipe curves. The movable core is so nicely manufactured that such curves as the letter S, and the stench traps, can be made with out help from the hands. This is a patented principle, and the
Akron works have a monopoly on it, and refuse to share with other parties.
The catalogues and circulars of the Akron manufacturers claim that they sell a vitrified pipe. But the word vitrified has a definite signification. It would require, if properly applied, that the clay should have been fused to a glass, or that it should have undergone incipient fusion, or that its free silica and fluxing impurities should have been made to combine. But none of these conditions are met. The fracture of the Akron pipe is not in the least vitreous. On the contrary, par ticles of the mass, such as pieces of shale, can frequently be seen separate and distinct from the body clay. The color also of combined oxide of iron and silica is dark, running from blue to black, while the color of uncombined Oxide of iron is red ; the color of the Akron pipe is red, showing that the impurities are not in a state of combination. But though the pipe is not vitrified, it is probably better than if it were, for the excess of the iron in the clay would tend to make it brittle, if it were in real combination. In other words, vitrification would present not only an undesirable but a dangerous quality in the sewer pipe. Judicious experimentation with powdered feldspar, salt, potash solution, or any fluxing agent would very soon establish the practicability and test the advantage of making the vitrified pipe throughout. The Akron, Ohio, sewer-pipe have as wide a distribution as any other similar manufactured product in Ohio ; they go in all directions and in all quantities.
Frederick H. Robinson, C. E., gives the following description of the manufacture of sewer pipe by the Delaware Terra Cotta Co., of Wilmington, Del.: "The works are situated on Brandywine Creek, between Heald and Eleventh streets, and close to the Philadelphia, Wil mington and Baltimore Railroad. They are equipped for the manufacture of all the standard sizes and shapes of sewer pipe, as well as of other work in terra cotta, and of fire-brick.
"The material of which the pipes are made is composed of three ingredients—two kinds of clay, and a sand and clay mixed. The first is a very strong clay obtained from brick yards in the northeastern part of the city. It underlies the clay of which brick are made. The second is a strong clay containing a red coloring matter, and is obtained from the south side of the Christiana River in New Castle Hundred, near the bridge on which the Delaware Railroad crosses the Christ iana. The third ingredient is a material composed of fire-clay and sand, and is obtained on the Christiana River in New Cas tle Hundred. These ingredients are mixed in the proportion by measurement of two parts of the strong clay first mentioned, one part of the clay containing the red coloring matter, and one part of the fire-clay and sand. Made in these proportions the mixture is placed in the wet-pan, where water is added. The wet-pan is a shallow circular iron pan, in which the clays are crushed and mixed by two iron wheels, following each other on edge around the pan, driven by a horizontal axle at tached to a vertical shaft. This pan is placed on the ground floor.