METHODS OF ANALYSIS. 59 
3 to 5 ce of concentrated arsenic-free sulphuric 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 
described 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 cc flask, cool, and make up to the mark. Take an aliquot of 200 cc for 
analysis, nearly neutralize with ammonia, heat, and pass hydrogen sulphid through 
for about half an hour. Filter off the precipitate, wash, dry, and burn in a porcelain 
crucible. Add nitric acid to dissolve the precipitate and heat till the copper is dis- 
solved. 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 3 milligrams, proceed as follows: Neutralize the 
copper solution with sodium carbonate, adding a trifling excess of the latter. Add 
1 cc of ammonia (sp. gr. 0.960) and titrate the dark-blue solution to the disappearance 
of the blue color with tenth-normal potassium cyanid 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 ammo- 
nium 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 ce aliquot of the liquid to dryness, take up the residue with 1 or 2 cc 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 dis- 
solved. Filter 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 eight hours, and let stand till the supernatant liquid is 
practically clear. Siphon off the clear liquid and filter. Use aliquots of the above 
liquid for determining carbonates, bicarbonates, chlorids, sulphates, calcium, magne- 
sium, and sodium. 
Follow the methods given for determining these constituents in waters in Bulletin 
91, Bureau of Chemistry, U. 8. Department of Agriculture, except in one particular, 
which is as follows: 
