1098 GEOLOGY OF OHIO. 
A most important point in the clay analysis was the determination: 
of the combined as distinguished from the “‘sand” silica. The method. 
was essentially that employed by Prof. Cook in the New Jersey survey. 
We used it as follows: 
One gramme of the clay, very finely powdered, was digested from. 
12 to 24 hours in a flask on a sand-bath with 10 to 165 cubic centimeters. 
of strong sulphuric acid; the temperature kept near the boiling point 
of the acid till the clay was completely decomposed. The mixture,. 
well cooled, was diluted ‘with cold water and filtered. The silica so 
obtained was weighed, then ground fine in an agate mortar; to it, 50 or 
60 ce. c. of a 15 per cent. solution of potassa was added, and boiled five 
minutes, filtered and washed. The residue was sand and undecomposed 
silicates, which, deducted from the weight of the total found above, 
gave the weight of the “combined silica” ; this again deducted from the: 
total silica found in course of the regular analysis, gave the silica 
present as sand. The results obtained thus were quite uniform, and 
corresponded well with the observed characters of the clays. 
The sulphuric acid solution of the clays so treated, after reduction 
with zine, served admirably for the titration of the iron they contained. 
Such is an outline of the analytical methods used in making the present: 
series of analyses. For convenience of reference, the tabulated results. 
of the survey work are given below. In the coal analyses, the “fuel 
ratio” or quotient of fixed carbon divided by the volatile combustible 
matter is given, as this eliminates the influence of the ash, and shows. 
the dryness, or otherwise, of the coal. 
The sulphur of the coal is not included in the totals of the analyses ; 
as it is not possible to tell just how much goes with volatile matter, and 
how much with fixed carbon, so it is always given separately. There 
are a number of analyses in the present volume not included in these 
tables. Such are, in most cases, taken from private analyses made in 
the laboratory, which I was permitted to use, but which are not part of 
the chemical work of the survey. 
\ 
