450 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



warping, and even partial cracking. This process is often carried 

 so far that the clay can be suspended in water. At one factory 

 on the Thames, a few years since, it was pumped and then float- 

 ed on for a quarter of a mile. The finest stock bricks were made 

 from this clay at a price of 25s. sterling per 1,000. Floating clay 

 is, however, only common in making porcelain; in this condition 

 iron is separated from it with magnets. 



Fire proof pottery consists of pulverized material — burnt clay, 

 plumbago, sand, or aluminate of lime, bound together by a plastic 

 clay. The last alone contracts both on drying and in firing — 

 the contraction commences afresh when it is exposed to a higher 

 heat; hence the importance of selecting the burnt clay from such 

 as has been fired at as high a temperature as the crucible is 

 intended to stand, and of using as large a proportion of it as pos- 

 sible to avoid warping and cracking in the kiln. Thorough 

 drying is of the utmost importance, to avoid hollows pro- 

 duced by escaping vapors. The application of great pressure 

 in moulding has enabled some manufacturers successfully to 

 reduce the amount of the plastic unburnt clay. A. most refrac- 

 tory brick has been made in this way containing ninety-five per 

 cent, silicious matter. Deville prepares aluminate of lime by 

 fritting together chalk and alumina. The cost of the last he esti- 

 mates at about $3 per cwt. Gas carbon the same chemist puri- 

 fies by treating it at a high heat with chlorine. Besides the use 

 of aluminate of lime to mix with alumina to form the body of 

 refractory ware, he also applies it as a lining. He makes a paste 

 of four parts calcined alumina, and one part of aluminate of lime, 

 well powdered and sifted, he quickly lays this on inside a clay 

 crucible, spreads with a piece of ware, and compresses it firmly 

 till perfectly polished, dries it and heats it to redness ; this var- 

 nish protected the silica of the clay crucible from the alumina 

 and fluor on which he had to operate. 



Other successful improvements in brickmaking are drying by 

 the heat from a cooling kiln, grinding marls, and rolling in lieu 

 of pugging; these are applicable to the manufacture. That of 

 most promise in use will probably be melting with gas, applied 

 directly to the metal inside, with or without fuel on the outside. 

 I am interested in perfecting this. 



The paper Avas accompanied by specimens of crucibles of vari- 

 ous makes, of one of curved outline to avoid any angle or change 

 of thickness near the bottom, designed by the writer, and construe- 



