6 AGRICULTURAL ANALYSIS 



7. General Principles of Sampling. The report of the chairman 

 of the committee charged with presenting to the Sixth Interna- 

 tional Congress at Rome the principles of sampling and sugges- 

 tions in respect of the method in which they should be carried 

 out contains the following directions. 4 



The subject of sampling for analysis may be very properly 

 divided into a general and a special part. I therefore shall dis- 

 cuss the problem in this way : First, with a brief statement of the 

 general principles which should underlie sampling, followed by 

 some special observations on sampling in special cases. 



8. Object of Sampling'. The object of securing a sample for 

 analysis is self-evident ; namely, that the sample should repre- 

 sent exactly, or as nearly as possible, the mean composition of the 

 whole deposit or substance from which it has been separated. 

 For this reason, much must be left in all cases to the sound 

 judgment of the person in charge of the sampling. This per- 

 son, whenever possible, should be the analyst himself, as no one 

 can judge so well as the one who is called upon to do the analyt- 

 ical work the character of the sample necessary to secure a 

 proper material on which the analysis is to be conducted. There- 

 fore, it is almost impossible to lay down any general principles 

 which should guide the expert in securing the sample of his 

 material unless the character of that material be known. 



9. Classes of Materials. The materials which are to be oper- 

 ated upon by the analyst are naturally divided into three states, 

 namely, gaseous, liquid and solid. These bodies pass gradually 

 from one state to another, and especially is this true of those 

 passing from a solid to a liquid condition. The transition from 

 the liquid to the gaseous form is very sharp and well defined. 



10. Sampling a Gas. In general, in the sampling of a 

 gaseous material it is only necessary that the gaseous contents of 

 the vessel, room or space should be thoroughly mixed in order 

 that any given portion of the gas may represent the whole sample. 

 This is especially true if the gases be of a mixed character or of 

 different specific gravities. Where, for instance, carbon dioxid 



4 Wiley, Methods of Sampling Materials for Analysis, Atti del VI Con- 

 gresso internazionale di Chimica applicata, 1907, 7 : 170. 



