1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 481 



allowed to settle several hours, then filtered, and the precipitate, 

 including filter, digested with 5-10 c.c. HNO3 and water until 

 copper was dissolved, solution filtered, a few drops of H2SO4 

 added, evaporated to fumes, and copper determined by elec- 

 trolysis with addition of 5-25 drops of HNO3. 



(h) 200 gms. soil was digested as above with HNO3 and 

 H0SO4, evaporated to fumes of H0SO4, digested with water, 

 filtered and washed up to 500 c.c, made alkaline with ammonia 

 and made up to 1000 c.c. After settling, 500 c.c. or 100 gms. 

 aliquot, was filtered ofi^ and copper determined as in (a). 



Waters. — Waters were evaporated to dryness, the residue 

 digested with sulphuric acid and water, filtered hot, excess of 

 HoSO^ evaporated, filtered into platinum dish, a few drops of 

 HNO3 added, and electrolyzed. 



Vegetation. — Air-dried samples were burned in a small sheet- 

 iron stove, the iron of which was found to contain no trace of 

 copper. Two samples of mistletoe, difficult to burn, were reduced 

 in a new muffle in gasoline assay furnace. The charred and 

 partly burned material was moistened with water, and concen- 

 trated HNO. added (100 to 200 c.c.) until effervescence ceased, 

 digested until in plastic condition, diluted with hot water and 

 filtered. Evaporated bulky filtrate to dryness, took up with 

 water and HNO.,, filtered (getting rid of much organic matter), 

 added about 20 c.c. H^SOj, evaporated to H.,S04 fumes, driving 

 off all but about 5 c.c. H0SO4, added water, filtered off insolubles, 

 made up filtrate to about 500 c.c, passed HoS, and proceeded as 

 usual for copper. 



Tlie completeness of the extraction of copper from vegetation 

 by the above method was verified as follows: The extracted, 

 charred residue from 2 lb. 8 oz. of dry corn leaves and blooms 

 in which 1.32 parts Cu per million was found (Sample 3529) 

 M^as removed from filter paper after washing, moistened with 

 H2SO4 and additionally burned in a porcelain dish, being finally 

 reduced, after again moistening with H0SO4, in a platinum dish 

 in the muffle. The resulting pink ash was then fused with three 

 parts of dry Na2C03 (Kahlbaum) and poured on clean porcelain. 

 The fusion was soaked in water with addition of H0SO4, evapor- 

 ated nearly to dryness, filtered from insoluble portion (lime, 

 salts, etc.), again evaporated and filtered, and a third time the 

 same, finally driving off excess of HoSOi and electrolyzing as 

 usual. A black precipitate of carbon but no Cu was obtained, 

 the same being true of a blank determination on the NaoCO-s used. 



Roots of plants grown in water cidtures or in soils must be 

 most thoroughly cleansed of externally adhering copper, since 

 this will introduce excessive errors where the content of copper 

 is small. Three methods of preparing roots for copper determina- 

 tion were employed : 



1. Roots grown in water cultures containing copper were 

 dipped for about ten seconds in 4 per cent HCl, immediately 



