﻿CLAYS FROM LUZON. 421 



as the oxide resulting from the decomposition of iron sulphides during 

 the original leaching of the clay material. In rough work it does little 

 harm, and in fine work, if present in particles of any size, it could easily 

 be removed by washing. In some of the Philippine kaolins the iron was 

 observed to be in tiny grains. However, there are many things which 

 are not shown by a chemical analysis. The results of such an analysis 

 are expressed as if all of the metals existed as oxides and the acids as 

 anhydrides. For example, gypsum (CaS0 4 ), calcium carbonate (CaC0 3 ) 

 and siderite (FeCCL) would be considered as present in the form of 

 lime (CaO) and sulphuric anhydride (S0 3 ), lime and carbonic anhydride 

 or carbon dioxide (C0 2 ), and ferrous oxide (FeO) and carbon dioxide, 

 respectively. In general, the fusibility of a clay increases directly in 

 proportion to the percentage of fluxing materials which it contains, but 

 there are exceptions depending on the mineral condition of the oxides. 

 If the oxide is present as a carbonate it generally fuses at a different 

 temperature than if it were present in the form of a silicate, and 

 furthermore, the fusibility of the various silicates of the same oxide com- 

 ponents vary. 



Some of the commonest minerals in clays are quartz, feldspar, calcite, 

 dolomite, gypsum, apatite, pyrite, other iron ores, mica, talc, serpentine, 

 hornblende, pyroxene, garnet, tourmaline, etc.; these are constituents 

 of the parent rock which have escaped decomposition. With the excep- 

 tion of quartz, the particles are usually too small to be detected by the 

 naked eye so that the "'rational analysis" 9 and the mechanical analysis, 

 to supplement the ultimate analysis, are resorted to in order to determine 

 the different percentages of the minerals present. It is not claimed that 

 these are accurate methods, but they are the best yet offered. When 

 a great many different kinds of mineral particles are present in one 

 clay, the methods become extremely complicated and with the common 

 clays are seldom used. For kaolin, where the only constituents are 

 kaolinite, feldspar, and quartz, the "rational analysis" becomes quite 

 simple and especially useful and as most clay workers understand the 

 relative importance of these constituents, when they are determined the 

 behavior of the clay can approximately be estimated. 



Eesearch in the direction of mechanical analysis has established methods 

 by which not merely the size of the grains, but also their shape, the 

 specific gravity of the materials, etc., may be determined; these are 

 important factors in establishing the usefulness of days. 



The determination of the fineness of the mechanical division is im- 

 portant, since it gives an idea of the lo^s when the material is prepared 

 for certain kinds of work. The following data by Mr. L. A. Salinger 

 show the proportion of certain sizes of grains in some of the clays 



"The actual method is given in almost any text on clay analysis, for example: 

 Ashby, H. M. : "How to Analyse Clay," Chicago (1901), 48. 



