112 CALORIFIC POWER OF FUELS. 



SAMPLING THE COAL. 



In all experiments for determining heat of combustion of 

 fuels, the sampling must be done with the utmost care, espe- 

 cially if the laboratory and working test are to be made at 

 the same time. Samples accurately representing the coal of 

 the working test must be kept in the laboratory, and when 

 coal is tested which contains foreign matter and considerable 

 moisture, too much care cannot be taken to prevent errors. 



The official method of the American Society of Mechanical 

 Engineers is given in the Appendix, and answers the purpose 

 very well. If very large quantities are to be sampled, remove 

 a portion from each cart-load and then re-sample these as per 

 directions above mentioned. 



It is not always necessary to resort to these methods. 

 When the coal comes from the same pit and level, experience 

 has shown that a piece which seems to agree with the general 

 character is usually sufficient. Care must be taken to avoid 

 samples having too much hanging-wall or bed-rock. For 

 twenty years the pure coal of Ronchamp taken from the 

 same pit has given the same calorimetric test, when it con- 

 tained from 10 to 20 per cent of ash. Lord and Haas* 

 showed that the same was true of many American mines, 

 especially in Ohio and Pennsylvania. This being true, we 

 could consider that in sampling we did not sample the coal, 

 but the impurities ; and that a sample showing the average 

 impurities would give all that was needed, as we would know 

 what the coal was. 



Care must be taken with regard to the moisture, and any 

 coal showing much external moisture must be examined as 

 near as possible to the original condition. For example, a 

 coal containing 10 per cent of moisture in the pile may, after 

 sampling, crushing, and resampling, lose all but 4 or 5 per 

 cent. If the moisture was determined in this coal while in as 



* Trans. Am. Inst. Min. Eng., Feb. 1897. 



