122  The  Technical  Analysis  of  Water.  {AmM2S,i£fm* 
Total  Solids. — ioo  c.c.  of  the  filtered  sample  of  water  are  evapor- 
ated to  dryness  in  a  platinum  dish  on  a  water  bath,  and  the  residue 
dried  at  ioo  c.c.  in  an  air-bath  to  a  constant  weight. 
Milligrammes  of  residue  multiplied  by  -583  equals  grains  per 
United  States  gallon.  (U'  S.  gallon  contains  58329-6  grains.)  If 
this  residue  is  taken  up  in  a  small  quantity  of  water  and  tested  with 
phenol-phthalein,  it  will  often  give  an  alkaline  reaction  when  no 
sodium  carbonate  is  present.  This  is  due  to  a  slight  decomposition  of 
the  magnesium  carbonate  into  magnesia,  while  drying  in  the  air-bath. 
A  sample  of  Lake  Michigan  water  shows  this  reaction  : 
Grains  per 
U.  S.  Gallon. 
Sodium  chloride  •  .  -578 
Sodium  sulphate  709 
Calcium  carbonate  4*316 
Magnesium  carbonate  .   .  .  1  -985 
Total  solids    .  8*162 
Free  carbonic  acid  .   7761 
Silica. — The  total  solid's  residue  is  taken  up  in  dilute  hydro- 
chloric acid,  evaporated  to  dryness,  and  taken  up  again  in  dilute 
hydrochloric  acid.  The  liquid  is  filtered,  the  insoluble  residue 
washed,  dried,  ignited  and  weighed,  which  is  the  silica. 
Milligrammes  of  residue  multiplied  by  -583  equals  grains  per 
United  States  gallon.  Nitric  acid  should  not  be  used  to  dissolve 
the  total  solid's  residue,  as  in  the  presence  of  sodium  chloride  there 
is  an  action  upon  the  platinum  dish,  due  to  the  formation  of  free 
chlorine. 
Iron  Oxide  and  Alumina. — 200  c.c.  of  the  filtered  sample  of  water 
are  acidified  with  hydrochloric  acid,  a  few  drops  of  nitric  acid  added 
and  boiled  to  remove  all  carbonic  acid.  The  liquid  is  allowed  to 
cool,  ammonium  chloride  added  and  then  ammonia  to  alkaline  reac- 
tion; allow  to  stand  for  ten  minutes,  then  filter.  The  precipitate 
washed,  dried,  ignited  and  weighed,  is  the  iron  oxide  and  alumina. 
Milligrammes  of  residue  multiplied  by -2916  equals  grains  per 
United  States  gallon. 
Calcium  Oxide. — The  filtrate  from  the  iron  oxide  and  alumina  is 
treated  with  ammonium  oxalate,  heated  and  allowed  to  stand  over 
night.  The  liquid  is  then  filtered,  the  precipitate  washed  and  dis- 
solved in  warm  dilute  sulphuric  acid,  which  is  then  titrated  with 
standard  decihormal  permanganate  of  potash  solution.  The  number 
