5i6 
Impurities  in  Water. 
Am.  Jour.  Pharrn. 
Oct.,  189u. 
The  number  of  bacteria  varied  much  in  different  parts  of  the 
same  cake. 
From  the  examinations  which  have  been  made,  it  appears  prob- 
able that  when  ice  forms  in  the  surface  of  a  pond  or  river  a  consider- 
able part  of  the  impurity  in  the  water  near  the  surface  is  entangled 
in  the  first  inch  or  less  in  depth,  and  that  the  ice  which  forms  below 
this  first  inch  contains  but  a  very  small  percentage  of  the  impuri- 
ties of  the  water.  If  snow  falls  upon  the  thin  ice,  causing  it  to 
sink  so  that  the  water  from  below  saturates  the  snow,  it  will  freeze 
without  purification  ;  or  if  rain  falls  upon  the  snow  and  freezes,  the 
ice  thus  formed  contains  the  impurities  of  the  snow  and  of  the  rain 
water  and.  of  whatever  else  may  have  settled  out  of  tr^e  air.  The 
cutting  holes  through  it,  gives  a  layer  of  ice  as  impure  as  the 
water  of  which  it  is  formed. 
The  purifying  effect  of  freezing  is  greater  upon  substances  in 
solution  than  upon  those  in  suspension.  This  is  confirmed  by  the 
fact  that  a  large  part  of  the  organic  matter,  one-half  or  three- 
quarters,  and  sometimes  more,  that  is  found  in  good  ice  is  of  parti- 
cles in  suspension,  and  is  readily  removed  by  filter  paper. 
From  the  average  of  all  the  water  and  ice  used  for  ice  supplies, 
which  they  have  examined,  they  find :  The  organic  impurities  of 
snow  ice  (the  sum  of  the  ammonias)  ===  69  per  cent,  of  the  impuri- 
ties of  the  water.  The  organic  impurities  of  all  the  ice  (except 
snow  ice)  =  12  per  cent,  of  the  impurities  of  the  water.  The 
organic  impurities  of  clear  ice  =  6  per  cent,  of  the  impurities  of 
the  water.  The  color  of  waters  was  removed  by  freezing.  The 
salt  of  the  waters  was  nearly  removed  by  freezing. 
Of  bacteria  there  were:  81  per  cent,  as  many  in  snow  ice  as  in 
the  waters  ;  10  per  cent,  as  many  in  all  other  ice  as  in  the  waters  ; 
2  per  cent,  as  many  in  clear  ice  as  in  the  waters. 
The  results  obtained  lead  to  the  conclusions :  That  while  clear 
ice  from  polluted  sources  may  contain  so  small  a  percentage  of  the 
impurities  of  the  source  that  it  may  not  be  regarded  as  injurious  to 
the  health,  the  snow  ice,  and  any  other,  however  clear,  which  may 
have  been  obtained  by  flooding,  is  likely  to  contain  so  large  a  per- 
centage of  the  impurities  of  the  source,  and,  with  these  impurities, 
some  of  the  disease  germs  which  may  be  in  the  source,  that  the 
Board  feels  bound  to  warn  the  public  against  using  ice  for  domestic 
method  often  pursued,  of  flooding  the 
