772  Miscellaneous  Results  from  the  Laboratory . 
It  will  be  observed  that  the  water  from  Dorset  Square  con- 
tains less  than  one-half  the  quantity  of  soluble  and  insoluble 
matters  found  in  the  other  specimens,  and  the  quantity  of 
ammonia  and  phosphoric  acid  are  in  the  same  proportion.  The 
first  sample,  however,  contains  a wonderful  excess  of  potash — a 
circumstance  not  easily  accounted  for — I have  reason  to  believe, 
however,  that  it  is  in  great  measure  due  to  the  influx  of  water 
from  the  streets  which,  under  certain  circumstances,  is  highly 
charged  with  salts  of  potash  derived  from  the  granite. 
For  the  sake  of  illustration,  we  may  be  allowed,  perhaps,  to 
calculate  the  money  value  of  the  ammonia  and  phosphoric  acid 
alone  of  the  poorest  of  these  samples  of  sewer  water — remember- 
ing always  that  the  least  important  of  the  ingredients  would  have 
a value,  when  the  immense  quantity  of  material  we  have  to  deal 
with  is  considered.  'Fen  thousand  gallons  of  sewer  water,  No.  2, 
would  contain  179,600  grains  of  ammonia,  or  rather  more  than 
'25b  lbs.  ; and  41,700  grs.  of  phosphoric  acid,  equal  to  86,000  grs. 
of  phosphate  of  lime,  or  about  12  lbs.  The  united  value  of  these 
two  substances — ammonia  being  taken  at  6 d.  and  phosphate  of 
lime  at  %cl.  per  lb.,  would  be  about  13s.  6c/. ; 100,000  gallons 
would  have  a value  of  6/.  15s.;  or  a million  gallons  of  6 71.  10s. 
The  quantity  of  water  supplied  to  London  daily  (and  running 
away  therefore  in  the  sewers)  is  said  to  exceed  40  million  gallons. 
Let  us  suppose  that  the  ammonia  and  phosphoric  acid  alone  of  a 
million  gallons  of  the  sewage  are  worth  50?.,  and  we  have  a daily 
sum  of  2000/.  swept  into  the  Thames,  or  nearly  three  quarters  of 
a million  each  year.  It  is  curious  that  the  yearly  expense  which 
is  incurred  by  the  farmers  of  England  in  the  importation  of 
guano  to  make  good  this  loss,  would  amount  to  a somewhat 
similar  sum.  There  is  no  kind  of  doubt  that,  agriculturally  con- 
sidered, the  sewage  is  more  than  worth  this  sum,  since  the 
Belgians,  who  take  great  care  of  human  manure,  consider  the 
excreta  of  each  person  worth  more  than  11.  per  annum,  and 
the  population  of  London  exceeds  millions. 
The  calculations  here  given  must  be  looked  upon,  as  we  before 
said,  merely  as  an  expression  of  the  great  agricultural  value  of  the 
sewer  water  of  towns,  and  not  as  an  attempt  to  fix  that  value  with 
any  approximation  even  to  the  truth. 
END  OF  VOL.  XI. 
TRINTED  BY  W.  CLOWES  AND  SONS,  SXAMTORD  STREET. 
