Freyn  states  that  the  following  are  average  figures  for  repair
accounts  for  a  blast  furnace  gas  station :

2J  per  cent  per  year  of  the  price  of  the  engines  and  electric
generators.
7  per  cent  per  year  of  the  price  of  the  cleaning  plant.
5  per  cent  per  year  of  the  price  of  the  air  compressor  used  for
starting.
2  per  cent  per  year  of  the  price  of  piping,  etc.
To  this  may  be  added  from  1  to  2  per  cent  of  the  cost  of  the
building  as  maintenance  for  the  building.
568  INTERNAL  COMBUSTION  ENGINES

Total  Operating  Costs  and  Cost  as  Compared  with  other
Prime  Movers  —  As  in  the  case  of  fuel  costs,  the  information
available  in  engineering  literature  on  total  operating  costs  is  of
two  kinds.  In  the  first  kind  the  estimates  are  based  entirely
upon  hypothetical  assumptions,  in  the  second  the  results  are
those  obtained  in  actual  operation.  Again,  the  latter  informa-
tion is  of  course  of  much  greater  value,  but  except  for  large  in-
stallations little  of  this  class  has  been  made  public.  Especially
as  regards  small  installations  of  gasoline,  oil  and  illuminating  gas
engines  there  seems  to  be  an  almost  absolute  lack  of  data  referring
to  total  operating  costs.  For  that  reason,  in  order  to  get  some
idea  of  costs,  it  will  be  necessary  for  the  time  being  to  depend  upon
cost  computations  based  on  assumptions.  In  any  concrete  case
these  assumptions  should  be  carefully  scanned  to  see  how  they
agree  with  actually  existing  conditions  before  forming  a  final  idea
of  operating  cost.
The  data  available  from  actual  practice  is  mainly  due  to  Mr.
