CHAPTER II. 



SAMPLING. 



Mr. It. Campbell, wlio was one of the committee 

 engaged on the coal testing plant of the United States 

 Geological Survey, at the Louisiana Purchase Exposition, St. 

 Louis, Mo., in a paper read before the American Institute of 

 llining Engineers in May, 1905, entitled "The Commercial 

 Value of Coal Mine Sampling," proposes that when sampling 

 a colliery, a fresh face of coal should be selected, free from 

 all powder stains and other impurities. A channel should 

 then be cut across the face of the coal from roof to floor 

 of such size as to yield at least five pounds' weight of coal for 

 each foot of thickness of the coal seam. All material encountered 

 in such a cut should be included in the sample, except part- 

 ings over quarter of an inch in thickness, and all concretions 

 of pyrites, or other impurities, greater than two inches in maxi- 

 mum diameter, and half an inch in thickness. The sample 

 should be broken down on a cloth protected by boards, so 

 that it shall not become mixed with any dirt on the floo-r. The 

 sample may be sent to the laboratory as cut, or it may be 

 quartered down to a convenient bulk at the face : in the latter 

 case it is first reduced in size to about three-quarters of an 

 inch. The operation of pulverising and quartering should be 

 done as rapidly as possible, to prevent loss of moisture con- 

 tent, and the sample should be at once sealed in a glass jar or 

 iin. An analysis of such a sample will show the grade of coal 

 that may be obtained by careful mining and picking, but in 

 ihe majority of cases the commercial output of the mine will 

 contain more sulphur and ash than shown by such an analysis, 

 because the sampling is done more carefully than the mining 

 on a larger scale, but the value of the latter may be approxi- 

 mated by multiplying the analysis by certain coefficients. The 

 coefficients are obtained by adding together the percentage of 

 ash or sulphur, as the case may be, of a given number of sam- 

 ples taken from the strips as ordinarily mined, and dividing 

 this by the total ash or sulphur found in the same number of 

 .specially taken mine samples. Since a sample is supposed to 

 represent what it is taken from in everything except bulk, 



