148 ADAMS AND PRATT. 



yellowish color when burned. Some pieces have been made in which the 

 silica has been increased by the addition of Laoag "silica." 



At San Pedro Tunasan the clay is washed in barrels or tanks. It 

 is placed in the first barrel with a large amount of water and is stirred 

 with a stick until a considerable percentage is in suspension. A part of 

 the water is then dipped from the barrel and poured through a sieve 

 having about 60 meshes to the inch, into a second barrel. After a few 

 minutes, when the clay is partially settled in the second barrel, the upper 

 part of the water is dipped or siphoned back into the first and the 

 process repeated. The washed clay which settles as a thin mud is placed 

 in the tank between the ovens and the chimney of the kiln and the excess 

 of water is evaporated by the heat from the latter when it is fired. At 

 Pandacan the clay is washed in pits. In the first pit it is mixed by 

 tramping in water which comes to the height of a man's waist. The 

 water with the clay in suspension is poured through a sieve into a second 

 pit, from which it may flow to either of two large drying floors. The 

 process of washing the clay by tramping is not an inviting occupation, 

 and stirring ,the clay in barrels is an awkward method. A log washer 

 turned by hand, an arrangement of screens and tanks, and a small pump 

 for running water to the washer from the settling tanks would be inex- 

 pensive improvements which would save labor and dignify the work. 



Characteristics of white clays. — Some idea of the character of the 

 white clays may be gathered from what has been noted concerning the 

 results obtained at Zobel's factory, where the utility of certain of them 

 was determined in a practical way. In addition, the chemical composi- 

 tion of the clays analyzed in the chemical division of the Bureau of 

 Science has been published by Dr. Alvin J. Cox, 1 together with some 

 physical tests. The writer in the following table has grouped certain 

 of these analyses according to localities. An analysis of Laoag silica by 

 L. A. Salinger is appended. 



1 Occurrence, Composition and Radio-activity of the Clays from Luzon. This 

 Journal Sec. A, (1907), 2, 6, 413-435. Laguna Clays, ibid. Sec. A, (1908), 

 3, 5, 377-388. 



