8 
C. A. LUDWIG 
that used throughout the city of Ann Arbor. During the first part 
of the experiments (winter of I9i5-'i6) it was pure coal gas;^ later 
(winter of 1916-'! 7 to Feb. i), it was a mixture of coal and water gas; 
and at the last (after Feb. i, 191 7) it consisted once more of coal gas 
only, except for the 5-day period, February 12-16, during which time 
a small amount of water gas was mixed in. The gas before and after 
February i, 191 7, analyzed approximately as follows: 
Before Feb. i After Feb. i 
CO2 1-2% 0.9-2.0% 
CnHo, 4-5% 3.5-4.5% 
O2 1-2% 0.8-1.5% 
CO 11-14% 6.0-7.8% 
CH4 25-30% 30-35% 
H2 40-50% 35-45%) 
N2 about 10% 8-11% 
The figures given here are not the result of specific analyses made 
for the purpose of this study, but are the result of the examination of 
a large number of student analyses. However, as the gas was used 
at various times over an interval of a year and a half or more, it seems 
that a more exact analysis would be little or no more valuable for 
interpreting the results. 
Ordinarily the gas was not washed. It was the original intention 
to do so, but this could not conveniently be done because the pres- 
sure in the pipes was too small to drive the gas through wash bottles. 
Moreover a few preliminary experiments with the gas showed that it 
did not exhibit extraordinary toxic properties toward the organisms 
used. It was therefore decided that as long as no very great toxic 
properties w^ere shown it was not necessary to remove traces of H2S, 
NH3, or other inorganic gases which presumably might be present and 
exert harmful influences. 
Effect on the Different Organisms 
In giving the results of the tests with illuminating gas, and with 
the other gases as well, a brief summary will be given for each species 
used, instead of giving a chronological account of the experiments or 
of giving single experiments in detail. 
2 I am indebted to Prof. W. L. Badger, of the department of chemical engineering 
of the University of Michigan, and to Mr. Chas. R. Henderson, chemist to the 
Washtenaw Gas Co., for the analyses and data given here concerning the illuminating 
gas used in these tests. 
