27 
CLAYS. 
Clay, in nearly all cases, consists principally of silicate of 
alumina, and contains water and many lesser constituents, 
such as iron oxide, lime, magnesia, and alkalies in greatly varying 
percentages. It often contains sandy matter made up of quartz, 
feldspar, and other minerals. 
In general, clay is a plastic material, the result of weather 
ing or breaking down of rocks. The clay particles exist in a 
finely divided state, making it, when wet, unctuous to the touch. 
The uses to which clay may be put depend upon its physical 
properties, such as its plasticity, the effect of drying, its be 
haviour at various temperatures, tensile strength, and its colour, 
both raw and after firing. 
Regarding the testing of clays, Dr. Merrill 1 says: “The 
most complete test of a clay now known would be obtained by 
use of analysis, coupled with a fire test made especially to develop 
such points as the analysis indicates to be weak ones. Fire 
tests are of two kinds—one consists in subjecting the clay to 
absolute heat without the action of any accompaniments, and 
the other in putting the clay through the course of treatment for 
which it is designed to be used. The former develops the 
absolute quality of the clay as good or bad, the latter proves or 
disproves the fitness of the clay for the work. The latter is 
better, of course, as a business test wherever it is practicable 
to use it.” 
Clays and their uses. 
Very complete data on the requirements as to composition 
=md physical properties of clays for special purposes may be 
ound in “Clays: Their Occurrence, Properties and Uses” by 
rofessor Heinrich Ries. 2 The description in detail of the vari 
ous clays of commerce would require more space than is available 
or the subject, and is outside the intended scope of this report. 
Mpir n >aSe 2d6, " Tlle Noil-Metallic Minerals, Their Occurrence and Uses,” by George P. 
" p John Wiley and So™. New York. 
ublished by John Wiley and Sons, New York.