[115, 116 



PART IV 



SAMPLES AND SAMPLING 



115. Large quantities of material are often valued by the 

 analysis of a couple of grams, or even less, which has been 

 taken from the bulk. Whether that analysis represents accu- 

 rately the composition of the whole quantity or not depends, 

 therefore, quite as much upon the care with which that two 

 grams has been selected as upon the accuracy with which the 

 analysis has been made. In fact, in every case where a sample 

 has been drawn from a large bulk of material, there is a certain 

 chance of error. The object of careful and scientific sampling 

 is to reduce this chance to a minimum. 



In practice all substances for analysis are sampled twice : 

 first, when the sample is taken from the bulk, and, second, 

 when the analyst selects from this first sample the portion upon 

 which he intends to experiment. 



As a rule this first operation is performed by the person 

 who wishes to have the analysis made, whilst the second is 

 done by the analyst. It would seem, therefore, at first sight 

 that the second was the only one with which the analyst need 

 be familiar j but the buyer or seller who wishes the sample to be 

 analysed has often no one to guide him in the sampling except 

 the analyst himself. Both operations are described in detail 

 in this chapter. . 



116. The Sampling of Minerals.— The only cases in 

 which the sampling of minerals concerns the agricultural analyst 



