256 On the Rain and Drainage - Waters at Rothamsted. 
It is obvious that the water falling on a rain gauge must be 
apt to carry with it into the receiver any impurity found on the 
surface of the gauge. Dust of various kinds is continually 
blown on to the surface of the gauge, which is also sometimes, 
though rarely, contaminated by the excrements of birds ; small 
insects also frequently find their way into the collecting vessels. 
With the view of removing as far as possible these sources of 
error, certain samples of rain were collected for analysis after the 
surface of the gauge had been washed by distilled water ; other 
samples were collected during the latter part of a shower, after 
the collecting surface had been washed by the earlier rain. The 
samples thus collected were for the most part received at once 
into clean bottles, without first entering the ordinary receiver 
of the gauge. Twenty-two samples of rain-water were in all 
collected with one or other of these precautions. The mean 
composition of these waters, and of the waters in the collection 
of which no such precautions were taken, is shown in the 
following Table : 
Table X. — Average Composition of Eain-Water collected both from a 
Washed Gauge, and Without special Precaution, in parts per Million. 
Total 
Solid 
Matter. 
Carbon 
Nitrogen as 
in 
Organic 
Matter. 
Organic 
Matter. 
Am- 
monia. 
Nitrates 
and 
Nitrites. 
Total 
Nitrogen. 
Chlorine. 
Hardness.* 
From washed gauge, \ 
22 samples . . . . j 
28-0 
0-64 
0-16 
0-30 
0-12t 
0-58 
21 
4-0 
Without special pre-l 
caution, 47 samples/ 
36-6 
1-03 
0-20 
0-41 
0-15t 
0-76 
3-G 
4-8 
It would appear from these figures that the water collected 
from the washed gauge was distinctly purer, especially in 
organic carbon and chlorine, than the rain ordinarily collected. 
These figures, however, probably exaggerate the effect produced 
by the natural impurities of the collecting surface, for the 
majority of the 22 samples being collected during the middle 
or latter part of a shower, really indicate the results obtained 
from a partly washed atmosphere as well as from a washed 
gauge. The extent to which the composition of the rairi is 
dependent on the washed or unwashed condition of the atmo- 
sphere is well illustrated by two of Dr. Frankland's analyses. 
* By "hardness" is understood the total lime and magnesia in a water, 
expreg.sed in parts of carbonate of calcium, 
t Mean of 11 analyses. % Mean of 23 analyses. 
