262 



University of California Publications in Agricultural Sciences [Vol. 3 



the residual nitrate determinations, we have seen that the mean of the 

 eighty-one samples amounted to 2.70 milligrams, with a probable error 

 of ± .05 milligrams and the standard deviation of the series 0.70 gram. 

 As already stated, the probable error of the mean is expressed as 



.6745 X o- 



E m 



V n 



Z.Q 



1. Laboratory Error. 



2. Res.'duat Nitrate 6"-24" 

 3 •■ •• |*-6* 

 4. Incubated Blanks 6"- £4" 



5 ■ - l'-6" 



6 Ammonium Sulfate 6"- £4* 



7 - - ,"-6" 



8. Blood 6 n -£4" 



9. •• |"-6" 



/ 4 3 16 



No of .Samples 



