﻿412 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  the 
  hammer 
  causes 
  it 
  to 
  be 
  lifted 
  and 
  dropped 
  in 
  rapid 
  succes- 
  

   sion. 
  The 
  hammer 
  weighs 
  two 
  kilograms. 
  According 
  to 
  the 
  

   speed 
  with 
  which 
  the 
  wheel 
  is 
  turned 
  the 
  hammer 
  can 
  be 
  made 
  

   to 
  deliver 
  a 
  greater 
  or 
  less 
  number 
  of 
  blows 
  within 
  a 
  given 
  

   period 
  (Schoch 
  p. 
  241). 
  

  

  Setting 
  strength. 
  It 
  has 
  been 
  found 
  that 
  the 
  final 
  strength 
  

   which 
  different 
  cements 
  attain 
  in 
  the 
  process 
  of 
  hardening 
  cor- 
  

   responds 
  with 
  the 
  rapidity 
  with 
  which 
  they 
  first 
  set. 
  For 
  in- 
  

   stance 
  a 
  cement 
  which 
  sets 
  very 
  quickly 
  and 
  which 
  may 
  attain 
  

   great 
  strength 
  in 
  a 
  few 
  hours 
  will 
  not 
  as 
  a 
  rule 
  compare 
  favor- 
  

   ably 
  after 
  a 
  month 
  or 
  two 
  with 
  one 
  which 
  sets 
  slowly, 
  while 
  

   Portland 
  cement 
  hardens 
  much 
  more 
  rapidly 
  than 
  natural 
  

   cements 
  but 
  sets 
  much 
  slower. 
  Of 
  course 
  there 
  will 
  be 
  a 
  varia- 
  

   tion 
  in 
  this 
  respect 
  depending 
  on 
  the 
  brand 
  of 
  the 
  cement, 
  and 
  

   those 
  which 
  are 
  considered 
  the 
  most 
  desirable 
  are 
  those 
  that 
  con- 
  

   tinue 
  to 
  harden 
  after 
  a 
  long 
  period. 
  According 
  to 
  Mr 
  Richard- 
  

   son/ 
  1 
  American 
  portland 
  cements 
  seem 
  to 
  gain 
  most 
  of 
  their 
  

   strength 
  in 
  a 
  few 
  days, 
  while 
  the 
  German 
  brands 
  will 
  be 
  inferior 
  

   in 
  strength 
  at 
  the 
  end 
  of 
  28 
  days 
  but 
  will 
  continue 
  to 
  increase 
  

   for 
  nearly 
  a 
  year 
  afterward 
  and 
  finally 
  attain 
  an 
  equal 
  strength. 
  

   Even 
  within 
  the 
  narrow 
  limits 
  of 
  composition 
  allowable 
  for 
  good 
  

   portland 
  cements 
  "there 
  is 
  still 
  a 
  chance 
  for 
  variations 
  which 
  will 
  

   produce 
  marked 
  differences 
  in 
  character. 
  Some 
  of 
  these 
  varia- 
  

   tions 
  have 
  been 
  noticed. 
  The 
  set 
  of 
  cement 
  is 
  much 
  influenced 
  

   by 
  the 
  amount 
  of 
  lime 
  specially 
  when 
  the 
  cement 
  is 
  under 
  burned, 
  

   or 
  by 
  a 
  large 
  amount 
  of 
  alumina. 
  As 
  a 
  rule 
  the 
  more 
  lime 
  a 
  

   cement 
  contains 
  the 
  harder 
  it 
  is 
  to 
  bring 
  about 
  the 
  proper 
  com- 
  

   bination 
  in 
  burning 
  and 
  the 
  higher 
  the 
  temperature 
  and 
  the 
  

   longer 
  the 
  heat 
  that 
  is 
  required. 
  When 
  properly 
  made 
  cements 
  

   with 
  a 
  high 
  percentage 
  of 
  lime 
  set 
  more 
  slowly 
  but 
  are 
  stronger 
  

   and 
  better 
  for 
  ordinary 
  uses. 
  

  

  Composition 
  of 
  American 
  portland 
  cement 
  

  

  The 
  American 
  portland 
  cements 
  are 
  made 
  from 
  a 
  variety 
  of 
  

   materials 
  which 
  resemble 
  each 
  other 
  chemically 
  rather 
  than 
  geo- 
  

  

  aBrickbuilder, 
  July, 
  1898, 
  p. 
  147. 
  

  

  