PREPARATION OF SAMPLE IN LABORATORY 1 9 



7. The labels are to be signed by the persons supervising the 

 sampling and are to be attached by means of the wax used in 

 sealing the bottles. 



8. The samples are to be kept in a cool, dark and dry place. 



9. Materials of heterogeneous composition must be sufficiently 

 reduced in size and mixed before bottling. 



23. Influence of State of Subdivision. The importance of good 

 sampling in securing reliable analytical data is shown by Riviere 

 by comparing the results of analysis of samples from different 

 parts of the same bulk material. 7 The substance examined was 

 dried blood. A sample received from a farmer was 

 passed as customary through a mill and contained 9.95 

 per cent, of nitrogen. This being lower than the guar- 

 anty, led to asking for a new sample of not less than 

 500 grams. In this sample there were found 11.20 per cent, of ni- 

 trogen. The sample was then divided into two portions by means 

 of a sieve. The fine part, 204 grams, contained 9.40 per cent, of 

 nitrogen and the coarse part 12.10 per cent. The two portions were 

 again mixed and a sample analyzed contained 11.14 per cent, of 

 nitrogen. It is evident from the above data that in transportation 

 the fine particles tend to go to the bottom and the large to be col- 

 lected on the top of the mass so that even were it well mixed at 

 the start, at the end of the journey samples from different parts 

 would show varying contents of nitrogen. 



24. Preparation of Sample in Laboratory. The method of 

 preparing mineral fertilizers for analysis has been given under 

 the directions for sampling. Many difficulties attend the proper 

 preparation of other samples, and the best approved methods of 

 procedure are given below. 



According to the directions given by the Association of Offi- 

 cial Agricultural Chemists the sample should be well intermixed, 

 finely ground, and passed through a sieve having circular per- 

 forations one millimeter in diameter. 8 The processes of grind- 

 ing and sifting should take place as rapidly as possible so that 

 there may be no gain or loss of moisture during the operation. 



1 L'Engrais, 1905, 20 : 233. 



Division of Chemistry, Bulletin 46, Revised, 1899 : n. 



