﻿CLAYS 
  OF 
  NEW 
  YORK 
  855 
  

  

  tile 
  which 
  allow 
  the 
  water 
  to 
  percolate 
  through 
  them 
  in 
  less 
  than 
  

   six 
  hours 
  should 
  be 
  rejected. 
  

  

  For 
  sewer 
  pipes 
  the 
  water 
  must 
  be 
  put 
  under 
  pressure, 
  which 
  is 
  

   done 
  by 
  closing 
  the 
  two 
  ends 
  of 
  the 
  pipe 
  with 
  plates 
  of 
  iron, 
  the 
  

   joints 
  being 
  tightened 
  by 
  means 
  of 
  rubber 
  bands 
  around 
  the 
  edges. 
  

   The 
  pressure 
  is 
  then 
  applied 
  by 
  means 
  of 
  a 
  piston 
  till 
  the 
  manom- 
  

   eter 
  shows 
  the 
  desired 
  pressure, 
  at 
  which 
  point 
  it 
  is 
  allowed 
  to 
  

   stand. 
  If 
  the 
  j)ipe 
  is 
  impermeable, 
  the 
  manometer 
  will 
  remain 
  

   at 
  that 
  point, 
  but 
  if 
  the 
  pipe 
  contains 
  a 
  flaw 
  the 
  liquid 
  in 
  the 
  mano- 
  

   meter 
  will 
  fall 
  and 
  moisture 
  will 
  appear 
  on 
  the 
  outside 
  of 
  the 
  

   pipe 
  at 
  the 
  point 
  where 
  the 
  flaw 
  is. 
  

  

  Breaking 
  strength 
  

  

  This 
  ,test 
  is 
  made 
  by 
  allowing 
  the 
  stone 
  to 
  lie 
  flat 
  on 
  two 
  parallel 
  

   supports 
  with 
  sharp 
  edges, 
  while 
  a 
  third 
  edge 
  is 
  caused 
  to 
  press 
  on 
  

   the 
  upper 
  surface 
  halfway 
  between 
  the 
  two 
  supports. 
  The 
  

   pressure 
  required 
  to 
  break 
  the 
  stone 
  is 
  then 
  measured. 
  If 
  the 
  

   upper 
  surface 
  of 
  the 
  stone 
  is 
  not 
  perfectly 
  flat, 
  it 
  can 
  be 
  made 
  so 
  

   by 
  laying 
  on 
  the 
  upper 
  surface 
  two 
  parallel 
  cleats 
  of 
  portland 
  

   cement 
  one 
  cm 
  wide. 
  See 
  " 
  Paving 
  brick 
  '', 
  p. 
  745. 
  

  

  Hardness 
  test 
  

  

  The 
  hardness 
  of 
  building 
  material 
  can 
  be 
  determined 
  by 
  means 
  

   of 
  Moh's 
  scale 
  of 
  hardness. 
  This 
  scale 
  is 
  made 
  up 
  of 
  10 
  different 
  

   minerals, 
  of 
  which 
  each 
  is 
  harder 
  than 
  the 
  precediug 
  one 
  in 
  the 
  

   series, 
  and 
  softer 
  than 
  the 
  succeeding 
  one. 
  The 
  order, 
  beginning 
  

   with 
  the 
  softest, 
  is: 
  

  

  1 
  Talc 
  

  

  2 
  Gypsum 
  

  

  3 
  Calcite 
  

  

  4 
  Fluorite 
  

  

  5 
  Apatite 
  

  

  6 
  Orthoclase 
  

   1 
  Quartz 
  

  

  8 
  Topaz 
  

  

  /' 
  

  

  