84 
VARIETIES. 
in  order  to  thank  God  and  the  French.  This  well  yields  not  less  than 
4300  litres  per  minute,  from  a  depth  of  54  metres.  A  fifth  well  has  been 
dug  at  Oum  Thiour,  yielding  108  litres  per  minute.  Here  a  part  of  the 
tribes  of  the  neighborhood  commenced  at  once  the  establishment  of  a 
village,  planting  at  the  same  time  hundreds  of  date  palms,  and  thus  giving 
up  their  former  nomadic  life.  The  last  well  is  that  of  Shegga,  where  soon 
an  important  agricultural  centre  will  spring  up.  There  is  no  doubt  but 
that  these  wells  will  work  in  these  parts  a  great  social  revolution.  The 
tribes  which,  after  the  primeval  custom  of  their  ancestors,  kept  wandering 
from  one  place  to  another,  will  gather  round  these  fertilising  springs,  will 
exchange  the  herdsman's  staff  for  the  plough  of  the  farmer,  and  thus  take 
the  first  steps  towards  a  civilization  which,  no  doubt,  will  make  rapid 
progress  in  Northern  Africa. — London  Pharm.  Jour,  from  Journal  of  the 
Society  of  Arts. 
Induration  of  Plaster  of  Paris  Casts. — A  Neapolitan  builder,  Signor 
Abate,  has  submitted  to  the  Academie  des  Sciences  numerous  speci- 
mens of  plaster  casts  as  hard  as  marble,  and  as  susceptible  of  receiv- 
ing a  fine  polish.  Instead  of  saturating  the  plaster,  as  is  ordinarily  the 
mode  of  proceeding,  with  eight  times  its  volume  of  water,  Signor  Abate 
combines  it  with  the  minimum  quantity  of  water,  whereby  porosity  is 
avoided,  and  the  consequent  liability  to  disintegration  of  the  mass  after 
exposure  for  a  certain  time  to  the  atmosphere.  For  this  purpose  the  plaster 
is  reduced  to  a  state  of  powder  in  a  horizontal  cylinder,  to  which  rotary 
motion  is  communicated,  and  steam  is  admitted  into  the  interior.  By  this 
means  the  quantity  of  water  absorbed  by  the  plaster  may  be  regulated  as 
desired.  The  plaster  thus  prepared  still  remains  in  a  powder,  and  in  that 
state  is  filled  into  moulds  and  submitted  to  hydraulic  pressure  for  a  short 
time.  The  moulded  articles  are  removed  from  the  moulds  and  found  to 
possess  great  compactness,  and  take  a  fine  polish. — London  Pharm.  Jour, 
from  Journal  of  the  Society  of  Arts. 
Factitious  Ivory  for  Photography.  By  J.  E.  Mayall. — This  invention,  by 
the  well  known  photographer  of  Regent  Street,  relates  to  the  use  of  arti- 
ficial ivory  for  receiving  photographic  pictures  instead  of  glass  or  paper. 
This  artificial  material,  which  possesses  all  the  properties  and  beautiful 
finish  of  ivory,  and  allows  of  any  subsequent  tinting  of  the  image,  and  the 
obtainment  of  superior  softness  in  the  semi-tints,  is  what  is  known  in 
France  as  Pinson's  artificial  ivory,  consisting  of  a  compound  of  gelatine 
and  alumina.  This  material  is  prepared  in  the  form  of  slabs,  for  the 
photographer's,  use  in  this  way : — The  tablets  or  slabs  are  composed  of 
gelatine  or  glue  in  its  natural  state,  and  are  immersed  in  a  bath  of  alumina, 
which  is  held  in  solution  by  sulphuric  or  acetic  acid ;  by  this  means  a 
complete  combination  takes  place  between  the  alumina  and  the  gelatine  ©r 
