AFeb^aryP?9aor6m'}     The  U.S.P.  as  a  Legal  Standard.  83 
namely,  the  evaporation  of  1, 000  c.c.  on  the  water-bath.  If  a  deter- 
mination of  total  solids  is  to  be  made  it  should  be  done  in  a  platinum 
basin  and  100  c.c.  evaporated.  No  proper  test  of  this  kind  can  be 
made  without  a  good  balance,  and  there  is  nothing  but  disadvantage 
in  evaporating  1,000  c.c,  especially  when  the  question  is  merely  a 
rough  ascertainment  for  control.  The  text  further  states  that  the 
residue  must  not  blacken  nor  emit  ammoniacal  or  acid  fumes.  Very 
few  natural  waters  will  fail  to  give  upon  evaporation  of  1 ,000  c.c.  a 
residue  that  does  not  blacken. 
It  appears,  however,  that  while  a  high  limit  is  fixed  for  the  solids, 
the  sample  is  scarcely  allowed  to  contain  anything  that  is  usually 
present  in  natural  waters.  Some  limits  are  fixed  at  almost  vanish- 
ing points.  Thus,  for  nitrates  the  delicate  and  inconvenient  diphenyl- 
amin  test  is  given.  This  will  probably  exclude  most  natural  waters, 
even  the  high-class  spring  and  river  waters  of  this  region.  The 
limits  for  sulphates  and  chlorides  seem  to  be  chosen  with  more 
regard  to  uniformity  in  the  reading  matter  than  in  the  standards. 
In  each  case  200  c.c.  of  the  sample  is  to  be  taken  and  0-5  c.c.  of  the 
particular  reagent  added.  In  the  chloride  test,  decinormal  silver 
nitrate  (or,  to  quote  the  stuffy  phrase  of  the  book,  "  tenth-normal 
silver  nitrate  V.  S.")  is  directed.  In  both  tests  the  liquids  must  be 
heated  to  boiling,  cooled  and  filtered.  For  the  actual  purpose  of 
these  tests,  boiling  is  not  needed,  and  it  is  especially  out  of  place  in 
the  case  of  the  test  for  chlorides.  The  direction  to  filter  the  liquids 
before  applying  the  second  phase  of  the  tests  is  also  an  excess.  If 
the  turbid  liquids  are  stood  aside  for  a  short  time  (the  chloride  test 
in  the  dark),  a  few  cubic  centimeters  of  the  clear  liquid  can  be 
decanted  and  the  test  applied. 
There  seems  to  be  a  marked  inequality  between  the  limits  allowed 
for  sulphates  (100  parts  per  million,  calculated  as  S04)  and  chlorides 
(8  87  parts  per  million,  calculated  as  CI).  These  limits  do  not  seem 
coordinated  nor  based  on  the  study  of  analytic  data. 
For  the  nitrite  test  the  naphthylamin  reaction  is  given.  This  is  a 
test  of  extreme  delicacy,  troublesome  in  application,  at  least  so  far 
as  the  preparation  of  the  reagents  is  concerned.  No  caution  is  given 
as  to  the  liability  to  error  from  the  common  occurrence  of  nitrites 
in  air  and  dust,  nor  is  it  pointed  out  that  deep  waters  will  often  give 
marked  reaction  for  nitrites,  and  yet  be  unobjectionable.  In  fact, 
the  whole  water-rubric  indicates  that  its  authors  are  unaware  that 
