38 INJURY BY SMELTER WASTES. 
CATTLE-FOOD MATERIALS. 
Joisture. 
Use the method given for determining moisture in the foliage of trees (p. 34). 
Total arsenic. 
Testing reagents.—Make a blank on the reagents and apparatus by boiling 
down 100 ce of nitric acid and 5 ce of sulphuric acid in the same kind of flask 
used for treating the samples, diluting and boiling down again to get rid of final 
traces of nitric and nitrous acid, again diluting and: finally running for two 
hours in the Marsh-Berzelius apparatus, described in the following section. 
Apparatus.—This consists of a small flask with a wide mouth, holding about 
100 ce. Through one hole of a rubber stopper a separatory funnel passes to 
the bottom of the flask. Through another hole in the rubber stopper passes 
the exit tube, which is in turn joined to a Liebig bulb containing a small 
amount of a solution of lead acetate to absorb any selenium, tellurium, or 
sulphur. This in turn is joined to a calcium chlorid tube, which is then at- 
tached to a long tube of very resistant glass. This glass tube is drawn out at 
one point rather small, nearly capillary, and the heat is applied about 0.5 inch 
before the drawn-out portion. Heat with two Bunsen burners, neither of which 
plays upon the glass directly but upon a piece of fine wire gauze wrapped 
around the glass. When preparing this apparatus for use, add about 3 grams 
of arsenic-free granulated zinc to the wide-mouthed bottle and then about 80 
ee of arsenic-free sulphuric acid (1 to 8). Let the apparatus run for fifteen 
minutes, after which apply heat for approximately twenty minutes to be sure 
that no arsenic is present. 
The apparatus is now ready for the addition of the extract from the cattle 
food. Run in and allow the action to continue for from one to two hours. 
Compare mirror thus formed with mirrors containing known amounts of ar- 
senic, which have been previously prepared with the same apparatus. The 
standard mirrors usually contain the following amounts of arsenic: 0.005, 0.01, 
0.02, 0.03, 0.04, 0.05, 0.06, and 0.07 mg of arsenic. These mirrors should be 
in sealed tubes and be remade about every three weeks, as they tend to fade a 
little upon standing. When not in use, they should be kept in a dark place. 
In case a larger amount than 0.07 mg of arsenic is obtained, cut off that 
part of the tube where the mirror is deposited, wipe carefully, and place in 
a desiccator. Then ‘weigh on an assay balance capable of weighing to the 
fifth place. Dip the tube in sodium hypochlorite solution to dissolve the ar- 
senic, wash with distilled water, then with alcohol, and finally with ether. dry, 
place in a desiceator, and weigh again. The difference in the two weights 
represents the arsenic from the amount of material taken. Both of these 
weighings must be made with the utmost care, as a small error at this point 
will cause a large error in the results. 
Standard solution.—To prepare the standard solution, dissolve 0.5 gram of 
dry chemically pure arsenious oxid in a sodium carbonate solution (free from 
arsenic) by boiling. Make weakly acid with arsenic-free sulphuric acid and 
make up to a liter. Measure out such a quantity of this solution in a liter 
flask as will give 0.01 gram of metallic arsenic and make up to the mark. Each 
cubie centimeter of this solution represents 0.01 mg of arsenic and is used for 
making the standard mirrors. 
Method.—Weigh 1 to 3 grams of the finely ground cattle food, according to 
the amount of arsenic present, and transfer to a 200 ce Jena flask. Add 25 cc 
