Sulphuric  Acid,  in  the  Rain-Water  collected  at  Rothamsted.  327 
but  the  chlorine  remains  high  throughout  the  winter  months, 
the  diminution  towards  the  summer  period  not  commencing  till 
April.  The  rain  of  March  has  yielded  the  highest  proportion 
of  chlorine  per  million  of  water,  but  this  is  partly  due  to  the 
small  rainfall  of  the  month.  Rather  more  than  two-thirds  of 
the  annual  supply  of  chlorine  is  contributed  by  the  winter 
months. 
In  the  next  Table  the  chlorine  determinations  in  72  monthly 
rainfalls  are  grouped  according  to  the  amount  of  the  rainfall,  and 
according  to  the  season  of  the  year. 
Table  VI. — The  Average  Amount  of  Chlorine  in  Monthly  Rain- 
falls of  different  Quantity,  in  Summer,  Winter,  and  the  Whole 
Year. 
Groups  of 
Rainfall. 
Summer  Months. 
Winter  Months. 
Whole  Year. 
& 
a 
cS 
{4 
w 
Mean 
Rain- 
fall. 
Chlorine. 
<3 
& 
a 
C!j 
y 
W 
Chlorine. 
P< 
a 
03 
y 
w 
Mean 
Rain- 
fall. 
Chlorine. 
Per 
Mil- 
lion. 
Lbs. 
per 
Acre. 
Rain- 
fall. 
Per 
Mil- 
lion. 
Lbs. 
per 
Acre. 
Per 
Mil- 
lion. 
Lbs. 
per 
Acre. 
Below  l inch  . . 
1 to  2 inches  . . 
2 to  3 inches  . . . . 
3 to  4 inches  . . 
Above  4 inches  . . 
3 
10 
9 
5 
9 
In. 
0*80 
1*56 
2*30 
3*55 
5-26 
3.58 
1-74 
1*40 
1*25 
0-81 
lbs. 
0*65 
0*61 
0*73 
1-01 
0*96 
6 
9 
7 
8 
6 
In. 
0*81 
1*52 
2*59 
3-44 
5*15 
5'76 
3*46 
2-65 
2*82 
2-23 
lbs. 
1-06 
1*19 
1.55 
2-20 
2-59 
9 
19 
16 
13 
15 
In. 
0-81 
1*54 
2*43 
3*48 
5-22 
5*04 
2-55 
1*98 
2*20 
1-37 
lbs. 
0*92 
0*89 
1-09 
1-74 
1*61 
36  2-88 
1*21  j 0-79 
36  2*64  2*84 
1-70 
72 
| 
2*76 
1*99 
1*24 
The  results  do  not  fall  into  a very  regular  series.  It  would 
appear  that  in  summer  the  supply  of  chlorides  is  very  limited, 
for  a lar°:e  increase  in  the  rainfall  is  attended  with  but  little 
rise  in  the  quantity  of  chlorine  brought  upon  an  acre.  In  winter, 
on  the  other  hand,  the  supply  of  chlorides  in  the  atmosphere  is 
so  constantly  renewed,  that  an  increased  rainfall  results  in  a 
considerable  addition  to  the  supply  per  acre.  The  rather  wide 
irregularities  in  the  composition  of  the  groups  of  rainfall  for 
the  whole  year,  are  principally  due  to  the  different  proportion 
of  summer  and  winter  months  which  enters  into  the  various 
groups. 
The  large  excess  of  chlorides  found  in  winter  rain  is  probably 
due  in  great  measure  to  the  chlorides  volatilised  during  the 
combustion  of  fuel  ; the  excess  in  question  is  too  uniform 
to  be  dependent  chiefly  on  the  action  of  strong  winds  blowing 
from  the  sea  ; it  is  also  remarked  in  calm  months  as  well  as  in 
stormy  weather.  Exceptionally  high  results  are,  however, 
probably  due  to  storms.  When  we  turn  to  the  nice  gradations 
observed  among  the  summer  months,  it  is  difficult  not  to  believe 
that  the  temperature  of  the  air  has  some  influence  on  the  results. 
