ACTION UPON NITRATES. 93 
filter, and add the filtrate to 150 c.c. of dilute (1 to 
16) hydric acetate. 
II. Sulphanilic acid, OF Ce 5 
Dilute (1 to 16) hydric acetate, 150 c.c. 
Keep these solutions in separate glass bottles, 
tightly stoppered, and mix in equal parts before 
use. 
To 3 c.c. of the solution to be tested, in a per- 
fectly clean test-tube, add gradually 2 c.c. of the 
test-solution. A red color develops of an intensity 
in proportion to the amount of nitrites present. 
The appearance of the color may be hastened by 
heating. 
If this test shows the presence of nitrites, test 
one-half of the remaining solution for ammonia 
with Nessler’s solution.' 
The presence of ammonia is shown by the im- 
mediate development of a yellow color or precipi- 
tate on the addition of a few drops of the test-solu- 
tion. 
When these tests are positive our inquiry has 
been answered. When negative the nitrates may 
have remained unchanged or may have been re- 
duced to free nitrogen. It is therefore necessary to 
determine whether the nitrates are still present or 
not, as follows: 
(2) Invert the tube containing the culture and 
evaporate to dryness the small amount of culture 
remaining on the inside of the tube. 
1 See Appendix, page 174. 
