_Reagents._—1. Sulfanilic acid solution. Dissolve 8.00 grams of the
purest sulfanilic acid in 1,000 cc. of 5 N acetic acid (sp. gr. 1.041)
or in 1,000 cc. of water containing 50 cc. of concentrated hydrochloric
acid. This is practically a saturated solution.
2. α-naphthylamine acetate or chloride solution. Dissolve 5.00 grams
solid α-naphthylamine in 1,000 cc. of 5 N acetic acid or in 1,000 cc. of
water containing 8 cc. of concentrated hydrochloric acid. Filter the
solution through washed absorbent cotton or an alundum filter.
3. Sodium nitrite stock solution. Dissolve 1.1 gram silver nitrite in
nitrite-free water; precipitate the silver with sodium chloride solution
and dilute the whole to 1 liter.
4. Standard sodium nitrite solution. Dilute 100 cc. of solution 3 to 1
liter, then dilute 50 cc. of this solution to 1 liter with sterilized
nitrite-free water, add 1 cc. of chloroform, and preserve in a
sterilized bottle. One cc. = 0.0005 mg. nitrogen.