THE CLAYS. — 645 
of thumb rule. With all the aid that it can render, practice is 
still empirical and blind, but without it, how much worse. The real 
value of analysis has never been tested in Ohio, or rather the analyses 
heretofore used have been the cause of the present distrust of their value. 
The older methods of reporting analysis yield but little to any but an 
expert. The fault is this: the elements are put together in a way that 
recognizes no structure; in fact, it rather conceals than brings it to 
notice, and those bodies are not classed together which are alike in 
nature or effect, so that predictions as to the qualities of clay have met 
with so little confirmation in experiment that practice has almost aban- 
doned the use of such tests. 
A few years ago, clays were believed to be what analysis indicated 
them ; silicates of alumina with no definite relation of base to acid and no 
two having much in common. But the study of their origin proves 
that clays are mixtures of a real clay, or kaolin base, with various sterile 
matters accompanying it in the parent rock. When this view was first 
announced, that one base is common to all clays, analysis was used to 
combat it. But in the work of the New Jersey Survey this point has 
been proved, and a mode of analysis used which illustrates composition, 
structure, and quality as well. The proof of the point was very ingenious 
and convincing. ‘The standard analysis of pure kaolin was compared 
with the average of the best New Jersey kaolins; laying aside the im- 
purities of the latter and recalculating on the basis of one hundred ; 
the two agreed very closely. Then in the analysis of common clays 
silica was divided into free silica or quartz, and that combined in the 
clay. Taking the combined water, combined silica and alumina, and 
calculating into per cents, it was found that the kaolin ratio was again 
obtained, and though some are too aluminous and some too silicious, 
still none vary widely, and the important conclusion is proved, viz., 
that kaolin is the base of all clays. 
The variations in the clay or kaolinite base, as it is now called, may 
be due to (a) free hydrated silica in the clay, (6) undecomposed feldspar, 
(c) other silicates than the normal one; as, silicates of lime, etc., (d) 
formation from other feldspars than orthoclase, or (e) errors of analysis ; 
any of which grounds can explain some variation. ‘One ground is very 
probably a constant source of error ; free hydrated silica is believed to be 
present in nearly all clays, but chemical analysis is not able to determine 
its amount with accuracy. 
