B. Mix thoroughly by swirling by hand. Do not use 
mechanical or magnetic stirrers. Add 10 ml. sulfuric 
acid solution and swirl again. Replace in cool water 
bath. 
C. Add 0.5 ml. brucine-sulfanilic acid reagent; swirl by 
hand and place in a well stirred boiling water bath that 
maintains a temperature of not less than 95°C. 
D. After exactly 20 minutes, remove standards, samples 
and blanks and immerse in a cold water bath. 
E. When thermal equilibrium is reached at room tempera- 
ture, dry off the tubes, and read standards and samples 
against reagent blanks at 410 millimicrons in a spec- 
trophotometer. Run at least two standards and two 
blanks with each batch of samples. 
6. CALCULATIONS 
A. Subtract reagent blanks from final absorbance readings 
of standards, and plot the resultant absorbance against 
mg. NO3-N/I1 (milligrams nitrate-nitrogen per liter). 
B.Correct the absorbance readings of the samples by sub- 
tracting their sample blank values from their final absor- 
bance values. 
C. Read the concentrations of NO3-N directly from the 
standard curve. 
D. mg. NO3-N 
mg./1 NO3 —N = 
ml. sample 
E. mg./1l NO3 = mg./1 NO3-N x 4.43 
7. EVALUATION OF RESULTS 
A. Ahigh level of nitrate (NO3) in the suspected coprolitic 
material combined with comparatively lower levels of 
NO3 in associated accompanying material from the 
pA 
