458 
ON  SOME  CEMENTS. 
When  the  cement  is  cold,  or  before,  it  may  be  removed  from  the 
water  and  wiped  dry,  when  it  is  fit  for  use. 
From  a  rough  experiment  I  made,  there  appeared  to  be  a  loss 
of  about  ^th  of  the  weight  of  the  materials  in  making  this  cement, 
arising  from  volatile  matter  and  impurities  in  the  pitch  and 
gutta  percha. 
Properties, — This  cement  is  of  a  black  color ;  when  cold,  it  is 
hard.  It  is  not  brittle,  but  has  some  degree  of  elasticity,  which 
is  increased  by  a  slight  increase  of  heat.  It  appears  to  be  not 
so  tough  as  gutta  percha,  but  more  elastic.  Its  tenacity  is  very 
considerable,  but  inferior,  if  I  mistake  not,  to  gutta  percha.  It 
softens  when  put  into  water  at  about  100°  Fahr. ;  and  if  the  heat 
is  gradually  increased,  it  passes  through  intermediate  states  of 
softness,  becomes  viscous  like  bird-lime,  and  may  be  extended 
into  threads  of  indefinite  length :  it  remains  in  this  state,  even 
when  exposed  for  some  time  in  a  crucible,  to  the  heat  of  boiling 
water,  at  212°  "Fahr.  When  heated  to  about  100°  Fahr.,  it  be- 
comes a  thin  fluid.  Water  appears  to  have  no  other  action  upon 
it  but  that  of  softening  it  when  warm  or  hot,  and  slowly  harden- 
ing it  when  cold.  The  cement  adheres  strongly,  if  pressed  on 
metal  or  other  surfaces,  though  water  be  present,  provided  such 
surfaces  be  warm. 
My  first  trials  with  this  cement  put  it  to  a  very  severe  test.  I 
used  it  as  a  substitute  for  plumber's  solder  in  repairing  the  lead 
gutters  on  the  roof  of  my  house,  which  were  cracked  in  several 
places,  and  admitted  water  freely  in  different  places,  and  also  to 
staunch  the  leaks  in  an  old  common  and  forcing-pump  attached 
for  yielding  a  supply  of  water  for  the  use  of  two  houses,  and 
raising  it  about  thirty  feet.  For  these  purposes  I  found  it  quite 
effectual.  All  that  was  necessary  in  the  case  of  the  gutters  was 
to  remove  with  a  brush  all  loose  earthy  matters  from  the  cracked 
lead,  slightly  warm  it  with  a  hot  iron,  then  pour  the  cement  in 
a  fluid  state  on  the  cracks,  so  as  to  cover  them  on  both  sides ; 
then  a  hot  iron  was  drawn  along  each  edge  of  the  cement  so  as 
to  soften  and  bevil  it  down  to  the  lead,  as  the  cement  has  inter- 
mediate degrees  of  fluidity,  and  is  thicker  or  thinner  as  it  is  ex- 
posed to  more  or  less  heat.  In  its  thicker  state  it  may,  perhaps, 
be  better  adapted  to  repair  cracks  in  lead  or  other  gutters ;  but 
a  crack  in  such  gutters  may  be  readily  filled  up  by  taking  a  piece 
