444 Messrs Purvis and Gourtauld, TJte limitations of the 
B. In the second series of experiments three solutions were 
made : one contained a copper-zinc couple ; the second a copper- 
zinc couple and a definite volume of a known strength of potassium 
nitrate; whilst a third contained the dissolved substance alone, 
with no couple and no potassium nitrate. In the sewage incuba- 
tions, the absence of nitrates was first proved by the indigo 
method. 
Name of 
substance, 
and strength 
of solution 
Amount of NH 3 produced 
in 100 c.c. in blank > 
experiment 
Amount of NH.. produced 
in 100 c.c. when in- 03 
cubated with couple 
Amount of NH 3 produced 
in 100 c.c. and including _ 
added KNO., and in- 
cubated with couple 
Excess of NH.. in B 
over that in f\ in Q 
parts per 100,000 
Excess of NH., in C 
over that in B PI 
parts per 100,000 
Amount of NH 3 equivalent 
to the nitric nitrogen added *n • 
to C i n parts per 100,000 
Albumin 
gm. 
gm. 
gm. 
gm. 
gm. 
gm. 1 
05 7 solution 
0-00224 
0-0028 
0-00297 
0 560 
0017 
0-60 
o-i % „ 
0-00004 
0-00005 
00007 
0 010 
0-650 
0-60 
O01°/o » 
0 000013 
0-00006 
0 0012 
0-047 
1-340 
0-60 
o-ooi 7 o „ 
0-000002 
0-00003 
00004 
0028 
0170 
0-12 
Peptone 
0 - l 7 solution 
0 000027 
0-00007 
0-00044 
0 043 
0-370 
0-60 
o-oi% „ 
0 000011 
0-00002 
0-00043 
0-009 
0 410 
0-60 
o-ooi, 7 o „ 
0-000013 
0000054 
000023 
0-041 
0-176 
o 12 j 
Sewage 
1 -0 7 solution 
0-00021 
0-00031 
0-00137 
0 100 
1-060 
0-60 
o-i 7 o „ 
0 000008 
0-000037 
0-00037 
0-029 
0-243 
0-60 
o-oi 7 e „ 
0-000005 
0000037 
0 00014 
0-032 
0-103 
0-12 
10 7 o „ 
0-0000057 
000009 
0-00057 
0 084 
0-480 
0-60 
0-01% „ 
0 000011 
0-000023 
0-00014 
0-012 
0-137 
0-12 
o-ooi 7 „ 
0 0000043 
0-00002 
0-000015 
0-015 
0-160 
0-12 
The results of the preceding tables may be considered from two 
points of view. First, there is the excess of ammonia produced by 
the couple alone ; and it is clear from the numbers in column D 
that the effect is to produce ammonia during the disintegration of 
the nitrogenous compounds in larger quantities than is produced 
when the couple is absent. It would be incorrect, therefore, to say 
