Aug.  1,  1895.]  Supj/!emf^nt  to  the,  “ 'rroj/ical  AgriciUtHriat." 
147 
chemical  formula  is  Si.  O.^  lu  a lice  .state  as 
well  as  ill  combiiiatioii  (a^  a coii.stitueiit  of  rocks 
and  miiieral.s)  silica  forms  about  half  of  the  solid 
matter  of  the  earth.  It  occurs  free  in  nature  in  two 
chrystalline  form.s  as  quart.^.  .iiid  tridymite,  and  in 
the  amor])hous  state  a.s  opal.  Calcedony,  flint  and 
agate  are  mi.\:ture.s  of  amorjihous  silica  with  quartz 
and  tridymite.  The  aluminium,  jiotassium.  cal- 
cium and  iron  silicates  mixed  in  diffei'ent  propor- 
tions constitute  a large  number  of  minerals.  The 
sand  used  in  the  preparation  of  mortar  though  not 
quite  free  from  impurities  is  almost  pure  quartz 
sand  or  silica.  Sand  is  mixed,  with  mortar  to 
distribute  the  contraction  caused  by  the  si  iked 
lime  inparting  with  the  water  with  which  it  is 
combined  oi  mi.xed  and- becoming  c inverted  into 
carbonate  of  lime.  The  presence  of  sand  in  mortar 
thus  prevents,  to  put  it. in  a practical  way,  cracks 
and  inequalities  in  the  plaster  when  it  dries. 
Beside.s  this,  it  is  believed  that  the  silica  also 
gradually  combines  with  lime  and  that  silicate  of 
lime  is  thus  formed,  which  tends  to  increase  tlie 
h.irdness  of  mortar  as  it  sets.  When  evenly  and 
carefully  applied  to  a stone  structure,  after  wetc- 
ing  the  bricks  in  order  that  they  may  adhere  tlie 
more  fimrly  by  the  mortar,  soaking  into  the  pores  of 
the  bricks,  the  adhesion  caused  by  good  mortar  is 
astonishing.  There  are  various  opinions  as  to  the 
superiority  of  some  qualities  of  sand  over  others. 
River  sand  for  instance  is  very  generally  con- 
sidered to  be  the  best  for  preparing  mortar,  but 
sea-sand  is  more  commonly  u.sed,  probably,  for 
one  reason,  because  it  is  more  conveniently  obtain- 
able. The  practically  pure  sandy  deposits  that 
occur  in  some  situations  (geologically,  no  doubt, 
old  river  beds  or  former  tidal  areas  of  the  sea)  are 
considered  by  some  to  be  quite  suitable  for  the 
purpose  of  mortar,  though  others  insist  on  the 
sand  coming  fresh  from  the  sea  or  rivers. 
Excellent  s.imples  of  mortar  are  prepared  by 
grinding  down  the  white  sand  from  these  dry- 
land deposits,  and  a beautiful  marble  surface 
produced  on  walls  by  polishing  the  mortar  after 
application  with  a , ■smooth  rock-crystal.  In  ihe 
preparation  of  this  speci.il  mortar,  lime  made  from 
shells  is  used. 
Ordinarily,  coral  lime  is  preferred  to  lime  pre- 
pared from  lime-st.one. 
In  mixing  mortar  it  is  advdsable  to  use  two  parts 
of  sand  to  one  of  lime,  for  setting  bricks  in  build- 
ings that  are  required  to  be  particularly  substan- 
tial ; for  ordinary  brick  work  and  jila.stering, 
of  sand  to  one  of  lime  may  be  used.  But  on  tliese 
practical  points  I would  rather  not  say  anything 
authoritatively.  My  endeavour,  in  this  paper, 
has  been  to  tell  you  something  about  the  chemistry 
of  mortar,  and  I trust  I have  explained  my 
subject  with  tolerable  clearness. 
RHEA  (R.UflE)  AND  CHINA  GR.ASS— A 
DISTINCTION. 
In  a note  on  Rhea  Eibre  by  Dr.  Watt,  in  the  Agri- 
cultural  Ledger  Series,  he  states  that  it  was  Roxburgh 
who  first  pointed  out  certain  differences  between 
the  plants,  called  by  the  above  names,  as  they  were 
grown  in  China  and  in  India.  Other  botanists 
following  him  also  attempted  the  separation  of 
the  two  forms.  Modern  writers,  however,  regard 
these  as  only  varieties  of  a common  simcies.  A 
few  ye.irs  ago  U.a  'Watt  himself  in  tlie  first  volume 
of  his  Dictionary  of  Economic  Products,  pointed 
out  that  whatever  views  botanists  might  nlti- 
maUdj’'  uphold,  there  was  a practical  consideration 
of  the  greatest  value  that  hinged  on  the  contro- 
ver.sy.  This  may  be  here  briefly  stated,  viz.,  that 
the  plant  that  yields  the  true  China  grass  is  met 
with  in  cultdvatioii  in  tracts  of  country  that  have 
a sub-temperate  climate,  while  the  Rhea— that  is 
to  say,  Malay  and  Bengal  stock— occurs  in  moist 
tropical  regions.  The  latter  is,  moreover,  a more 
robust  plant,  has  longer  and  narrower  leaves  with 
white  toraei.tum  on  the  veins  of  the  under-.surface 
only;  while  the  former  has  large  broad  leaves 
with  the  base  subcor  late,  cuncite  and  densely 
coated  below  witli  adpre.ssed  white  hairs.  Now, 
if  this  distinction  holds  good,  it  would  obviously 
be  a mistake  to  attempt  the  cultivation  of  the 
temperate-loving  plant  in  the  tropical  plains  of 
India.  Prom  time  to  time  fresh  supplies  have 
been  imported  from  China  and  distributed  all  over 
this  country,  so  that  India  may^  fairly  be  char- 
acteri.sed  as  having  fully’  attempted  the  acclimati- 
sation of  the  China  grass,  but  done  little  or 
nothing  to.vards  endeavouring  to  extend  the 
production  of  what  (for  the  sake  of  convenience 
of  e.xpressionl  sve  may'  characterise  as  its  indi- 
genous stock.  O.i  this  subject  Mr.  W.  t.  Thiselton 
Dyer  (Director  of  the  Royal  Botanic  Gardens, 
Kevv)  has  written  : — 
‘‘The  point  raised  by'  Dr.  Watt  from  the  botani- 
cal point  of  view,  has  been  dealt  with  by  Sir 
.loseph  Hooker  in  the  Flora  of  British  India.  Th^ 
further  distinction  in  adaptability  to  climatic 
conditions,  which  chiefly  concerns  planters,  has 
been  observed  in  nearly  every  part  of  the  world 
where  these  pilants  are  grown  for  fibre  purposes. 
The  Ramie  or  Rhea,  properly  so  called,  may  be 
looked  upon  as  the  tropical  representative  of  the 
China-grass,  and  it  is  on  that  account  probably' 
better  adapted  for  cultivation  in  hot  and  moist 
countries.  Under  such  conditions  it  is  a very 
robust  plant  and  y'ields  valuable  fibre. 
‘‘  Whether  this  fibre  is  at  its  best  really  as  good 
as  the  liest  China-grass  {Boehmeria  nioea)  is  a 
point  that  appears  not  to  have  been  definitely 
settled.  It  may'  turn  out  to  be  simply'  a question 
of  Soil  or  climate.  At  Kew  we  find  we  cannot 
succe.ssfully'  grow  B.  ten'icissima  in  the  open 
where  B.  nivea  itself  remains  in  the  ground  all  the 
winter,  and  furnishes  in  the  summer  a large  crop 
of  vigorous  stems.  The  China-grass  may',  there- 
fore, give  a larger  and  better  supply  of  fibre  under 
cool  conditions,  wherea.s  tlie  Riraie  or  Rhea  may 
do  equally  well  under  essentially'  tropical  condi- 
tions. The  question  as  regards  India  may  be 
settled  by'  cultivating  under  various  conditions  of 
climate  and  soil  authentic  specimens  of  each  plant, 
and  by  instituting,  as  suggested  by  Dr.  Watt,  a 
careful  chemical  and  microscopic  analy'sis  of  the 
fibres  y’lelded  by  Indian-grown  plants  of  what  are 
known  to  be  tlie  true  Boehmeria  nivea  and  the 
true  B.  tenacissimaA 

GENERAL  ITEMS. 
The  Mark  Lane  Express  thus  refers  to  the  value 
of  seaweed  as  a manure  : — Seaweed  decomposes 
very'  rapidly  and  should  either  be  applied  fresh  as 
a top-dressing  or  ploughed  in  at  once  on  arable 
land.  It  also  makes  an  e.xcellent  compost  with 
any  vegetable  refuse,  ditch  parings,  peat,  mould. 
