1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 483 

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



ings. 



Twenty-fifth wash 

 Twenty-ninth wash 

 Thirty -first wash 



H,S test 



distinct 



Quantitative by 

 electrolysis 



.00005 gm. Cu 

 .00000 



Samples vary as to number of washings required to remove 

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

 copper usually ceases to be extracted by COo 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 coi^per 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. 



Example 



Sample 2a grown in 

 soil containing 

 0.05% copper 

 Ash in sample 

 Co]3per in ash as- 

 sumed as soil 



Net copper assumed 



Dry 



matter 



Ash 



Gms. Cu 



.3561 gm. 

 .0386 



10.84% .00013 5 



.000019 



Pts. Cu 

 per 



million 



322 



.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 DETERMINATION OF COPPER 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 asli 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 



