36 INJURY BY SMELTER WASTES. 
from time to time. Dilute the solution, filter, and wash residue. Return 
filtrate to the porcelain dish, add 8 to 5 ce of concentrated arsenic-free sul- 
phuric acid, and evaporate on the steam bath to a small bulk. Remove from 
_the steam bath and treat on a hot plate till dense white fumes arise. Cool, 
dilute, boil, and filter into a +100 cc flask. Make up to the mark and use 
aliquot portions for determining arsenic by means of standard mirrors, or 
weighing the mirrors, in the Marsh-Berzelius apparatus, which method is de- 
scribed under the determination of arsenic in cattle-food materials. Test 
all reagents and apparatus by running a blank before using to be sure of 
absence of traces of arsenic. 
Total copper. 
Digest 10 grams of soil on the steam bath for four hours with 100 cc of 
25 per cent nitric acid, using a porcelain evaporating dish with a watch-glass 
cover. Dilute, filter into a 500 ce flask, cool, and make up to the mark. Take 
an aliquot of 200 ce for analysis, nearly neutralize with ammonia, heat, and 
pass hydrogen sulphid through for about half an hour. Filter off the precipi- 
tate, wash, dry, and burn in a porcelain crucible. Add nitric acid to dissolve 
the precipitate and heat till the copper is dissolved. Filter through the 
smallest sized filter and determine copper by either of two methods according 
to the amount of this element present. 
If copper is present in excess of 2 or 8 milligrams, proceed as follows: 
_ Neutralize the copper solution with sodium carbonate, adding a trifling excess 
of the latter. Add 1 ce of ammonia (sp. gr. 0.960) and titrate the dark-blue 
solution to the disappearance of the blue color with tenth-normal potassium 
eyanid which has been standardized against a known amount of copper by 
exactly the same method as that just described for the determination of the 
copper present. 
If the copper is present in very minute quantities, proceed as follows: Add 
ammonium hydroxid to the copper solution until slightly in excess, heat on 
the steam bath a few minutes, filter on the smallest sized filter, wash, and 
evaporate the filtrate in a porcelain dish to 2 or 3 ec, cool, add acetic acid a 
drop at a time until the solution is just acid, and then add 5 drops of 4 per 
cent potassium ferrocyanid. Compare this color with the color produced by 
treating a known amount of copper dissolved in a similar amount of water 
in a porcelain dish with acetic acid and potassium ferrocyanid in exactly 
the same way as just described. 
Water-soluble copper. 
Weigh out 100 grams of soil, transfer to a flask, and treat with 1,000 cc 
of water. Shake the flask occasionally during eight hours, then let stand 
till the supernatant liquid is practically clear. Siphon off the clear liquid and 
filter. Evaporate a 750 cc aliquot of the liquid to dryness, take up the residue 
with 1 or 2 ce of nitric acid by the aid of heat, dilute, and filter. Heat the 
filtrate, pass hydrogen sulphid through for half an hour, filter, wash, dry, and 
burn the filter, and precipitate in a porcelain crucible. Add nitric acid to 
dissolve the precipitate and heat till the copper is dissolved. Fiiter through 
the smallest sized filter and determine copper by one of the methods described 
above under ‘*‘ Total copper.” 
Soluble salts. 
Weigh out 50 grams of soil, transfer to a flask and treat with 1,000 cc of 
water, shake the flask occasionally during 8 hours and let stand till the super- 
natant liquid is practically clear. Siphon off the clear liquid and filter. Use 
