10 



Many other substances were also tried, but as tbe effects were not in 

 all cases decisive they have not been included here. It will be 

 observed that among the solutions tried, tannic acid, ammonia, and the 

 alums were the most active in increasing the tensile strength. 



On first thought these results are by no means easy to interpret, 

 Tannic acid and the alums are astringent and of decidedly acid reaction 

 in their water solutions, whereas ammonia is decidedly alkaline in 

 reaction and detergent in its action. On the other hand, if alum is 

 added to clay suspended in water to form a "slip," it will have a floc- 

 culating or coagulating effect upon the colloid particles, causing them 

 to settle rapidly. Tannic acid and ammonia appear, in most cases, 

 to have a deflocculating effect, and some clays, suspended in dilute 

 ammonia, show no indication of settling after the lapse of several 

 months. It is known that the colloid structure of clays is selective in 

 its action, that is to say, tannic acid and ammonia will be taken out of 

 solution and retained in the porous particles of a clay. Tin's absorp- 

 tion then probably affects to some extent the flotation of the particles. 

 In the writer's opinion the action of reagents in increasing the binding 

 power of clays is twofold : (1) Deflocculation produces a better distri- 

 bution of the colloid particles or a so-called "puddling" of the clay; 

 (2) the colloids present are modified and developed, if not actually 

 formed, by the reactions which take place. A further discussion of 

 this interesting subject is of too technical a nature to be given here, 

 but the question will be more fully treated in other publications. 



USE OF CLAYS. 



The various uses of clays is shown by the following list originally 

 compiled for Mineral Resources, United States, 1891, published by the 

 U.S. Geological Survey : l 



Domestic. Porcelain, white earthenware, stoneware, yellow ware, and Kotfk- 

 ingham ware for table service and cooking; majolica stoves; polishing brick, 

 bath brick, fire kindlers. 



Structural. Brick, common, front, pressed, ornamental, hollow, glazed, adobe, 

 terra cotta ; roofing tile ; glazed and encaustic tile ; drain tile ; paving brick ; 

 chimney fines; chimney pots; doorknobs; fireproofing; terra cotta lumber; 

 copings ; fence posts. 



Hygienic. Urinals, closet bowls, sinks, washtubs, bath tubs, pitchers, se\ver 

 pipe, ventilating flues, foundation blocks, vitrified bricks. 



Decorative. Ornamental pottery, terra cotta, majolica, garden furniture,* 

 tombstones. 



Minor uses. Food adulterant ; paint fillers ; paper filling ; electric insulators ; 

 pumps; fulling cloth ; scouring soap ; packing for horses' feet; chemical appa- 

 ratus ; condensing worms ; ink bottles ; ultramarine manufacture ; emery wheels ; 

 playing marbles ; battery cups ; pins, stilts, and spurs for potter's use ; shuttle 



1 Clays of the United States East of the Mississippi River, by Heinrich Hies, 

 U. S. Geol. Sur. Professional Paper No. 11. 



