‘STATE GEOLOGIST. 121 
material after heating with CaO and treating with HCl and Na,CO, the 
higher is the value of the clay for hydraulic cements. 
The method of working adopted by the two investigators named 
was as follows: 
Samples of marl were taken, in the shape of lumps of walnut size 
which were heated in a gas furnace to a temperature of about I100° C. 
without pulverizing or mixing, for two hours. These burned samples 
were pulverized, treated with HCl and Na,CO, the residue being weighed 
after thorough washing. The value of the respective marls was ex- 
pressed inversely by the per cent. of residue. 
In order to prove that these tests really stand for expressions of the 
hydraulic value of the marls, Lunge and Schochor proceeded to grind the 
materials and to make cements of them by burning to vitrification and 
erinding the resulting clinker. The burning was done in a small test 
kiln. The hydraulic cements thus produced were subjected to the usual 
cement tests, which proved strikingly that for the marls examined, the 
hydraulic value was a function of the solubility of the clayey constituents 
when treated as mentioned above. ; 
Upon studying the results obtained by Lunge and Schochor, Prof. 
Edward Orton, Jr., suggested the use of this method for the testing of 
clays in regard to their suitability for cement manufacture. The investiga- 
tors just named restricted their method to marls, and although it is ex- 
tremely valuable for the determination of the hydraulic value of any one 
marl, yet its results are not generally applicable and must always be 
restricted to this class of material. The factors in this method are 
evidently the variables of the clay substance, coarse and fine quartz, coarse 
and fine feldspathic matter, and in addition to this the lime contents. This 
evidently may in some cases give rise to conflicting results, as for instance, 
when there are two marls to be examined of which one has a coarser 
grain of sand, but a higher content of lime than the second marl, which 
is fine grained and has a higher percentage of combined silica but a 
lower per cent. of lime. The method now suggested for clays adopts a 
constant amount of lime, thus eliminating one variable. 
The identity of structure which Lunge and Schochor are so careful 
to preserve by burning the materials in lumps is not interfered with by 
reducing them, without grinding, to the size of a 40 mesh sieve. In fact 
by burning the materials in lumps the outside factor of irregularity due 
to natural formation is so great as to introduce an additional source of 
error. For a product as homogeneous as cement the consideration of the 
bed structure is entirely unnecessary. 
Thus the process of the Ohio Geological Survey is intended to de- 
termine the hydraulic factor of a clay by reducing the latter without 
grinding, with the assistance of water, so that it will pass through a 
40 mesh sieve, care being taken not to reject the coarser material left on 
the sieve nor to break up any particles by grinding. When in the state 
