CLAY MANUFACTURES. 679 
sand, grains of iron and other detrimental impurity. The slip runs into 
a large tank called the “ agitator” in which it is kept slowly stirring by 
rotating arms, so that the slip is always of the same consistency, and no 
clay settles to the bottom. ‘The bolting apparatus is worked by steam 
power and is usually vibrated by a cam and a spring. So far all wash- 
ing processes agree, but beyond, there is a choice of methods. The 
slowest way is by boiling, as already described in the door-knob works. 
The more rapid is by pressing. The effect on the character of the 
clays is different in the two cases; boiling simply evaporates as steam 
all the water introduced, leaving any soluble alkaline or earthy 
matter behind, so that the effect of washing and boiling is simply 
mechanical, removing lumps and making the clay homogeneous and plas- | 
tic. But by the other process the water is squeezed out of the clay by 
pressure, and as it goes, of course, the soluble matters go with it, and it 
would probably exercise some beneficial effect on a clay impregnated with 
the alkalies or alkaline earths. The action of the water might be made 
more marked in eliminating impurities by adding a small amount of some 
solvent suited to the case. If the alkalies are found in grains of felds- 
par or mica, or are present as soluble silicates, washing would eliminate 
them. Hence we can see the reason why yellow-ware and stone-ware 
both made from the same clay would not vitrify at equal heat. The presses 
used are all of the same style. They are frames of wood about 7 ft. 
long, 2 ft. high by 5 in. wide, standing on edge, about twenty to twenty- 
four of them in line; they are fitted to join together by lateral screw 
pressure into one long box. ‘To each compartment is fitted a stout piece 
of duck or sail-cloth, which by proper folding acts as a closed bag, and 
from an orifice in the top of it it receives a stream of the fluid slip; the 
clay is retained in the bottom of the bag and the water runs out. The slip 
is supplied at a high pressure by a stout force pump; these bags become 
full of clay in time, and the water runs out through holes in the bottom of 
the box, coming out towards the end of the process nearly as clean as be- 
fore use. The box, when full, is composed of parallel sections of clay of 
the size of the interior of the frame and separated from it and each other 
by the sail-cloth. When full, the water ceases to flow out at the bottom. 
The apparatus is taken apart, and the clay from each section rolled up 
- in a wad, and carried away to a sweat-room to await use. The cloths 
can be used indefinitely. The capacity of the press varies with the 
number of chambers it has, and is about 100 pounds to a section, 
