ON THE CARBONIC ACID, ORGANIC MATTER, ETC., IN AIR. 
67 
Open places. 
Day. 
Open places. 
Night. 
Close places. 
Night. 
No. of 
No. of 
No. of 
determi¬ 
nations. 
Lowest. 
Highest. 
Mean. 
determi¬ 
nations. 
Lowest. 
Highest. 
Mean. 
determi¬ 
nations. 
Lowest. 
Highest. 
Mean. 
Carbonic acid 
20 
2-2 
5'3 
3-8 
9 
3 0 
56 
4-1 
7 
3-2 
5-4 
4-2 
Organic matter . 
Total micro- 
34 
1-1 
16-8 
9-5 
9 
2 2 
6'7 
3'9 
7 
5-6 
11-8 
8-4 
organisms: — 
6 
0-3 
2-2 
1-2 
2 
o-i 
0-2 
0-15 
6 
0 
1-3 
0-54 
Bacteria . . 
6 
0 
1-9 
0-7 
2 
0T 
0-2 
015 
5 
0 
1-3 
0'49 
Moulds . . 
6 
0-2 
1-3 
0'5 
2 
0 
0 
0 
5 
0 
0-1 
0 0 4 
The above Table shows : (1) That, with the exception of the carbonic acid, all the 
determinations made in open places gave much lower results during the night than 
during the day. The organic matter was reduced to less than one-half, and the micro¬ 
organisms to nearly one-tenth, of what they were during the day. The carbonic acid, 
though represented as being slightly less during the day, was practically the same; 
for, according to the method of treating the data, the night would show a slightly 
higher or a slightly lower result than the day. (2) That in all cases the determina¬ 
tions made during the night gave higher results for close than for open places. With 
the exception of the carbonic acid, this difference is very considerable. Though the 
figures for carbonic acid are near, yet the average for close is distinctly higher than for 
open places. The average for open places is possibly a little too high, as any other 
method of treating the data would give a somewhat lower result. (3) That, with 
the exception of the carbonic acid, even close places at night give a lower average 
than open places by day, thus proving distinctly that both organic matter and micro¬ 
organisms are considerably less during the night than during the day. The moulds 
more particularly showed a large reduction. 
The influence of day and night, and the effect of town and suburban conditions, is 
shown in a conclusive manner by the next Table. This Table records a series of hourly 
observations made simultaneously at two different places for a period of twenty-four 
hours. One of the places at which the samples were collected was the large open 
playground of the Dundee High School in the centre of the town, and the other a 
somewhat elevated position on the western outskirts overlooking the Tay. The 
prevalent direction of the wind was about south-west, i.e., across and down the valley 
of the Tay from the Ochil Hills. The standard solution employed in both cases was 
the same; and the analyses, apart from the collection of the samples, were carried out 
by the same person. The results of the full Table (p. 68) may be summarised as 
follows:— 
