CHEMICAL  STONE-WARE  MANUFACTURE. 
535 
gas.  The  pressure  should  then  be  regulated  by  the  stop-cock  a. 
This  arrangement  prevents,  to  some  extent,  the  blowing  down 
of  the  flame  when  the  pressure  of  the  gas  in  the  pipe  beyond  the 
fixed  stop-cock  happens  to  be  suddenly  lessened. — London 
Pharm.  Journ.  May^  1861. 
CHEMICAL  STONE-WARE  MANUFACTURE. 
The  manufacture  of  Chemical  Stone-ware  has  latterly  assumed 
so  high  a  degree  of  importance  that  we  have  thought  it  desirable 
to  bring  before  our  subscribers  the  following  account  of  the 
various  materials  employed,  the  different  processes  to  which  they 
are  subjected,  and  the  numerous  uses  to  which  the  manufactured 
articles  can  be  applied.  We  have,  therefore,  paid  a  visit  to  the 
potteries  of  Messrs.  J.  Cliff  and  Co.,  Princes  street,  Lambeth, 
and,  by  the  kind  courtesy  of  the  firm,  have  been  enabled  to  trace 
the  various  steps  of  the  manufacture,  from  the  reception  of  the 
raw  material  to  its  conversion  into  the  finished  article. 
The  materials  employed  are  chiefly  white  clays,  obtained  from 
the  counties  of  Devon  and  Dorset,  with  a  certain  amount  of 
kaolin,  or  China  clay,  from  Cornwall ;  and  for  glazing  purposes 
a  proportion  of  Cornish  stone,  felspar,  &c.  To  the  former  are 
added  sand,  ground  flint,  and  other  clays  of  a  more  or  less  in- 
fusible character,  according  to  the  quality  of  body  required,  from 
Maidstone  Wortley,  near  Leeds,  and  Newcastle-on-Tyne ;  and 
for  certain  kinds  of  ware  a  large  proportion  of  pounded  broken 
earthenware,  technically  known  as  rough  stuff,  or  grit,  is  used. 
On  referring  to  the  "Mineral  Statistics,"  published  by  the 
Geological  Museum,  we  find  that  the  various  kinds  of  pottery 
and  fire  clay  produced  in  England  alone  in  the  year  1858, 
amounted  to  upwards  of  four  hundred  thousand  tons,  and  that 
the  estimated  value  was  nearly  three  hundred  thousand  pounds. 
These  totals  do  not  include  the  clays  used  for  the  manufacture 
of  bricks  and  tiles. 
The  Devonshire  clays  are  purer  than  those  of  Dorset,  and  are 
used  for  the  manufacture  of  the  smaller  wares.  Those  of  Dorset 
contain  a  certain  admixture  of  lime  and  iron,  rendering  them 
less  pure,  and  consequently  of  less  value.    They  are  used  in 
