230 Bulletin 80 



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 HoSO^ 

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

 trolysis with addition of 5-25 drops of HNO,. 



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

 H2SO4, evaporated to fumes of H2SO4, 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 off and copper determined as in (a). 



Waters. — Waters were evaporated to dryness, the residue 

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

 H2SO4 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 HNO3 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 HNO3, filtered (getting rid of much organic matter), 

 added about 20 c.c. HoSO^, evaporated to HoSO^ fumes, driving 

 off all but about 5 c.c. H2SO4, added water, filtered off' insolubles, 

 made up filtrate to about 500 c.c, passed H2S, and proceeded as 

 usual for copper. 



The 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) 

 was removed from filter paper after washing, moistened with 

 H2SO4 and additionally burned in a porcelain dish, being finally 

 reduced, after again moistening with H2SO4, in a platinum dish 

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

 parts of dry NaoCO. (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 HsSOj and electrolyzing as 

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

 the same being true of a blank determination on the NaoCOs used. 



Roots of plants gi-own in water cultures 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 



