﻿43 
  

  

  anotlier 
  composition. 
  Tlie 
  coating 
  should 
  l)e 
  made 
  of 
  a 
  

   good 
  strong 
  mortar, 
  about 
  one 
  part 
  of 
  lime 
  to 
  two 
  of 
  

   sand, 
  and 
  after 
  it 
  is 
  applied 
  it 
  should 
  be 
  allowed 
  to 
  set 
  

   for 
  several 
  (hiys 
  under 
  cover 
  before 
  the 
  prepared 
  slates 
  

   are 
  made 
  up 
  into 
  series 
  in 
  frames 
  of 
  various 
  sizes 
  and 
  

   put 
  into 
  the 
  water. 
  Cement 
  alone 
  does 
  not 
  answer 
  the 
  

   purpose, 
  as 
  it 
  becomes 
  so 
  extremelj^ 
  hard 
  in 
  the 
  course 
  

   of 
  time 
  that 
  it 
  cannot 
  be 
  readily 
  removed 
  from 
  the 
  sur- 
  

   faces 
  to 
  which 
  it 
  has 
  been 
  applied, 
  which 
  of 
  course 
  ren- 
  

   ders 
  it 
  practically 
  useless. 
  The 
  slates 
  after 
  they 
  are 
  

   prepared 
  were 
  fastened 
  into 
  frames 
  about 
  two 
  feet 
  high, 
  

   the 
  ends 
  being 
  let 
  into 
  notches 
  about 
  an 
  inch 
  or 
  so 
  

   apart. 
  Tn 
  tliis 
  way 
  a 
  dozen 
  could 
  be 
  made 
  up 
  into 
  one 
  

   frame, 
  wliicli 
  held 
  them 
  liorizoutally 
  at 
  a 
  good 
  distance 
  

   from 
  the 
  l)ottom 
  and 
  far 
  enough 
  opart 
  to 
  allow 
  the 
  water 
  

   to 
  pass 
  readily 
  through 
  between 
  the 
  slates, 
  giving 
  the 
  

   floating 
  embryos 
  a. 
  good 
  (diance 
  to 
  lix 
  themselves 
  to 
  the 
  

   mortared 
  surfaces. 
  Other 
  frames 
  were 
  made 
  of 
  an 
  oblong 
  

   shape, 
  one 
  foot 
  wide 
  and 
  six 
  or 
  eight 
  feet 
  long, 
  the 
  edges 
  of 
  

   the 
  long 
  side 
  pieces 
  were 
  deeply 
  notched 
  with 
  the 
  saw 
  

   every 
  three 
  or 
  four 
  inches 
  apart 
  to 
  receive 
  the 
  one 
  edge 
  

   of 
  a 
  slate, 
  which 
  was 
  held 
  in 
  a 
  vertical 
  position 
  when 
  the 
  

   frame 
  was 
  laid 
  down 
  horizontally. 
  Some 
  of 
  these 
  frames 
  

   would 
  hold 
  twelve 
  or 
  fourteen 
  slates 
  in 
  position 
  at 
  once. 
  

   In 
  other 
  cases 
  the 
  slates 
  were 
  simply 
  coated 
  with 
  mortar 
  

   and 
  laid 
  in 
  rows 
  horizontally 
  upon 
  parallel 
  poles 
  sup- 
  

   ported 
  al)ove 
  the 
  Ixjttom 
  a 
  few 
  inches. 
  In 
  other 
  cases 
  

   again 
  the 
  slates 
  were 
  suspended 
  upon 
  galvanized 
  wire 
  

   by 
  the 
  four 
  corners, 
  in 
  a 
  tier 
  of 
  4 
  or 
  o, 
  about 
  an 
  inch 
  

   apart. 
  I 
  also 
  susi)ended 
  them 
  singly 
  by 
  means 
  of 
  gal- 
  

   vanized 
  wire. 
  I 
  did 
  not 
  however 
  obtain 
  the 
  same 
  results 
  

   frcmi 
  all 
  of 
  the 
  apparatus. 
  The 
  conditions 
  weie 
  such 
  

   however 
  in 
  most 
  cases 
  as 
  to 
  make 
  it 
  extremely 
  difficult 
  

   to 
  make 
  a 
  fair 
  (•om])arison. 
  Where 
  the 
  slates 
  were 
  in 
  a 
  

   horizontal 
  position 
  more 
  mud 
  seemed 
  to 
  be 
  deposited 
  on 
  

   the 
  upper 
  side 
  which 
  interfered 
  with 
  the 
  attachment 
  of 
  

   the 
  spat 
  on 
  that 
  side, 
  while 
  the 
  comparative 
  shade 
  below 
  

  

  