110 ANNUAL REPORT 
SAMPLING LIMESTONE AND CEMENT ROCK, 
In working with these harder rocks the churn drill is indispensable, 
it being worked either by hand or by power. In every case it will pay 
to obtain the service of a professional driller, such as are found in every 
district. At a comparatively small depth, drill holes are rapidly put 
through limestone material with a power drill. 
If the rock to be sampled is in a quarry or other exposure, u vertical 
channel should be cut into the face, from top to bottom, sufficiently deep 
to remove all weathered rock, so that the sample obtained may be a true 
one. By drilling and the proper use of explosives such work can be 
carried on quite rapidly, but should in every case be done under the 
guidance of an experienced quarryman. For rapid work the diamond 
drill has given very good results. 
In preparing samples for analytical work it goes without saying that 
great pains must be taken in order that they be average samples. Unless 
care is taken to do this, the entire work is of little or no value. The 
original sample should always be as large as possible and the entire quan- 
tity should be crushed together to 8 mesh and then intimately mixed and 
quartered down to about ten pounds. ‘This should be again ground so that 
it will pass a 20 mesh sieve, and again quartered down until the amount for 
a laboratory test has been obtained, about 500 grams, which must then be 
put through a 100 mesh sieve. One cannot be too careful or painstaking 
in this preliminary work, as its thoroughness governs the value of all 
subsequent work. 
The Ohio Geological Survey carried on the sampling as follows: 
The samples came from the field in sacks, provided with pasteboard 
tags on the outside and wooden tags on the inside of each sack, the weight 
varying from 50 to 150 pounds. Wherever necessary the sample was 
dried on a hot.plate dryer and then crushed by means of a small jaw 
crusher; usually the entire sample was run through in this manner, 
if the sample was a large one. ‘The material was now thoroughly mixed, 
it being fine enough to pass through an 8 mesh screen. If the sample 
was.less than 45 pounds, all of it wae put into a specially designed dry 
ball-mill and of course in this case it was not necessary to mix it before 
putting in the mill. This machine, made of chilled cast iron, proved 
extremely valuable in this work, since it not only ground the 8 mesh mate- 
rial to anydesiredfineness,but at the same time it produced a sample almost 
ideal as to uniformity. The grinding was done by Greenland pebbles, which, 
of course, introduced some silica, but so small in amount that it could be 
safely neglected. In another part of this report the machine is described 
in detail. The usual charge of the mill was from 40 to 45 pounds. 
When a charge was ground the lid of the machine was removed and 
the flint balls, together with the ground material, dumped into a long 
box placed beneath the mill. From this box the whole charge was 
