232 Bulletin 80 



(4) Coarse roots of field corn grown in soil containing tail- 

 ings. 



HjS test Quantitative by 



electrolysis 



Twenty-fifth wash distinct 



Twentv-ninth wash .00005 gm. Cu 



Thirty-first wash .00000 



Samples vary as to number of washings required to remove 

 the last trace of copper, but the definiteness with wiiich, finally, 

 copper usually ceases to be extracted by CO, water indicates 

 completeness of the operation. This is further emphasized by 

 the comparatively large amounts of copper which are then found 

 in root systems thus cleansed. 



3. A third method of preparing roots for copper determin- 

 ation, involving less labor than by washing in CO^, water, is as 

 follows: Cleanse roots thoroughly in clean water with a camel- 

 hair brush, dry, burn and weigh the ash, then estimate total 

 copper. Determine copper in soil shaken from sample, assume 

 ash as all soil and deduct copper in this amount of soil from 

 total copper found in ash. Results by this method are low, but 

 not seriously in error if sample is thoroughly washed. 



Pts. Cu 

 Dry per 



Example matter Ash Gms. Cu million 



Sample 2a! grown in 

 soil containing 

 0.05% copper .3561 gm. 10.84% .000115 322 



Ash in sample .0386 



Copper in ash as- 

 sumed as soil .000019 



Net copper assumed .000096 270 



The correction introduced reduces parts per million of copper 

 from 322 to 270, which latter figure is conservative in character. 



Of the three methods above described. No. 2 is undoubtedly 

 most exact, but is extremely laborious and time-consuming. 



THE DETEEMINATION OF COPPEE IN SMALL AMOUNTS OF 



PLANT ASHES 



The ash is placed in a platinum dish without previous pulver- 

 ization and moistened with concentrated sulphuric acid in suf- 

 ficient quantity to bring all parts of the ash in intimate contact 

 with the acid. The material is then thoroughly stirred and 

 heated on a sand bath until fumes of SO,, begin to come off, then 

 allowed to cool and a sufficient quantity of hydrofluoric acid 

 added to bring the acid in contact with the whole mass, then 

 allowed to stand for at least half an hour and again heated until 



