﻿394 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  nearly 
  as 
  great 
  a 
  tensile 
  strength 
  at 
  the 
  end 
  of 
  from 
  one 
  to 
  2S 
  

   as 
  the 
  magnesian 
  cements. 
  They 
  resist 
  frost 
  better 
  than 
  the 
  

   latter 
  but 
  at 
  the 
  age 
  of 
  a 
  year 
  very 
  often 
  have 
  not 
  strength 
  

   enough 
  and 
  are 
  at 
  times 
  inferior, 
  more 
  brittle 
  and 
  crystalline 
  with 
  

   a 
  tendency 
  to 
  deteriorate 
  in 
  strength. 
  The 
  perfectly 
  prepared 
  and 
  

   carefully 
  made 
  cements 
  of 
  this 
  class 
  are 
  the 
  best 
  natural 
  cements 
  

   in 
  the 
  world. 
  The 
  Roundtop 
  cement 
  of 
  the 
  Potomac 
  valley 
  is 
  

   typical 
  of 
  the 
  highest 
  grade 
  of 
  the 
  lime 
  cements 
  as 
  the 
  numerous 
  

   Rosendale 
  brands 
  are 
  of 
  the 
  magnesia 
  class. 
  

  

  Manufacture 
  of 
  natural 
  cements. 
  Physical 
  properties 
  of 
  the 
  stone. 
  

   Of 
  primary 
  importance 
  is 
  the 
  density 
  of 
  the 
  rock. 
  A 
  light 
  

   rock 
  does 
  not 
  burn 
  well 
  or 
  give 
  a 
  cement 
  of 
  suitable 
  volume, 
  

   weight 
  or 
  density. 
  The 
  specific 
  gravity 
  at 
  78° 
  F. 
  should 
  not 
  be 
  

   below 
  2.7, 
  and 
  preferably 
  be 
  2.8. 
  Some 
  stones 
  have 
  a 
  specific 
  

   gravity 
  of 
  only 
  2:65, 
  but 
  they 
  are 
  inferior. 
  The 
  beet 
  rock 
  is 
  

   obtained 
  from 
  those 
  portions 
  of 
  the 
  quarry 
  which 
  are 
  beyond 
  

   the 
  range 
  of 
  weathering. 
  Kichardson 
  gives 
  the 
  following 
  den- 
  

   sity 
  for 
  the 
  Rosendale 
  rock: 
  

  

  Nearest 
  surface 
  

  

  Light 
  rock 
  , 
  2.83 
  

  

  Dark 
  rock 
  2.849 
  

  

  Medium 
  

  

  Light 
  rock 
  2.815 
  

  

  Dark 
  rock 
  2.841 
  

  

  Deepest 
  

  

  Light 
  rock 
  2.827 
  

  

  Dark 
  rock 
  2.845 
  

  

  The 
  Fort 
  Scott, 
  Kan., 
  rock 
  which 
  is 
  nearer 
  the 
  surface 
  ha& 
  

   a 
  density 
  according 
  to 
  Mr 
  Richardson 
  of 
  only 
  2.73, 
  the 
  Round- 
  

   top 
  rock, 
  Maryland, 
  is 
  2.731, 
  the 
  hydraulic 
  limestone 
  of 
  Illinois 
  

   is 
  only 
  2.667 
  and 
  does 
  not 
  produce 
  as 
  dense 
  a 
  cement. 
  It 
  is 
  also 
  

   desirable 
  that 
  the 
  various 
  ingredients 
  of 
  the 
  rock 
  should 
  be 
  a» 
  

   thoroughly 
  mixed 
  in 
  as 
  possible. 
  If 
  the 
  sand 
  is 
  coarse 
  or 
  the 
  

   clay 
  in 
  lumps 
  or 
  the 
  carbonate 
  in 
  pockets 
  by 
  itself 
  the 
  rock 
  is 
  not 
  

   adapted 
  for 
  making 
  cement. 
  Generally 
  mere 
  inspection 
  will 
  sup- 
  

   ply 
  information 
  on 
  this 
  point, 
  and 
  the 
  size 
  of 
  the 
  particles 
  can 
  be 
  

  

  