364 
VARIETIES. 
tion  of  coal,  mixed  with  cinders  such  as  escape  from  the  grate  of  a  furnace, 
and  are  called  "  escarbilles."  Coke  and  charcoal  have  produced  nothing 
satisfactory. 
M.  Deville  informs  me  that  he  has  found  no  difference  between  the  fused 
and  welded  platinum.  We  add,  however,  that  he  has  not  compared  the  electro- 
chemical properties  of  these  metals,  nor  the  action  on  light. — Silliman's 
Journal,  May,  1853. 
On  the  Use  of  Fatty  Acids  as  a  Source  of  Light.  By  J.  Cambaceres. 
The  author  has  endeavored  to  reduce  the  cost  of  fabrication  of  these  fatty 
acids  by  employing  such  materials  as  will  furnish  a  by-product  more  valu- 
able than  the  sulphate  of  lime  obtained  by  the  saponification  with  lime.  He 
has  succeeded  in  preparing  in  this  way  sulphate  of  alumina,  a  substance 
largely  used  in  dyeing. 
For  this  purpose,  he  first  saponifies  the  fat  with  potash  or  soda  lye.  The 
soap,  containing  an  excess  of  alkali,  acts  upon  clay  so  as  to  dissolve  the 
alumina,  which  combines  with  the  fatty  acids,  forming  a  soap  which  is  in- 
soluble in  the  alkaline  liquid,  and  the  alkali  is  again  set  free.  The  alumina- 
soap  may  be  separated  as  a  gelatinous  precipitate  by  an  excess  of  alkali,  by 
a  large  quantity  of  water,  or  by  saline  solutions.  The  gelatinous  character 
of  the  alumina  soap  facilitates  its  decomposition  by  acids,  and  the  alumina 
salt  may  be  obtained  by  evaporation,  during  which  the  silica  likewise  taken 
up  by  the  alkali  is  separated. 
The  decomposition  of  soap  by  alumina  is  undoubtedly  owing  to  the  af- 
finity of  alumina  for  fat  acids  and  the  insolubility  of  the  alumina  soap  in 
alkaline  lye. 
In  order  to  prepare  the  fat  acids  in  this  way  at  the  least  possible  cost, 
care  must  be  taken  that  in  washing  the  soap  as  little  alkali  as  possible  be 
left.  However,  a  residue  of  alkali  is  not  objectionable  on  any  other  grounds, 
for  when  the  soap  is  decomposed  with  sulphuric  acid,  it  forms  alum.  It 
follows,  therefore,  from  these  facts,  that  in  places  where  clay  free  from  iron 
can  be  procured,  the  fabrication  of  acetate  and  sulphate  of  alumina  may 
very  advantageously  be  combined  with  that  of  stearic  acid,  because,  accord- 
ing to  the  author,  the  relative  cost  of  production,  notwithstanding  the  high 
price  of  alkalies,  is  less  than  when  lime  is  employed  in  the  saponification. — 
Chem.  Gaz.,  May  2,  1853,  from  Comptes  Rendus,  vol.  lvii.  p.  144. 
Manufacture  of  Paper. — It  is  well  known  that  paper  which  is  very  white 
when  first  made,  often  becomes  yellow  some  time  after  being  used.  The 
yellow  color  is  not  always  uniform,  but  often  comes  out  in  spots  more  or 
less  large  of  a  circular  outline,  and  a  rusty  tint.  In  some  Paris  manufac- 
tories, this  defect  (which  is  incorrectly  attributed  to  an  alteration  of  the 
fibre)  is  remedied  in  a  simple  manner,  and  as  the  process  of  discoloration 
may  not  be  commonly  used  in  America,  judging  from  some  paper  I  have 
seen,  I  make  a  brief  mention  of  the  subject. 
