182  VARIETIES. 
become  soluble  when,  by  a  preliminary  distillation,  they  have  lost  25  per 
cent,  of  their  weight.  This  result,  announced  by  the  author  in  1862,  was 
the  subject  of  a  former  memoir  presented  to  the  Academy  of  Sciences. 
The  present  paper  contains  some  new  researches,  the  conclusions  of  which 
may  be  stated  as  follows  : — 
1st.  The  above  resins,  when  heated  to  a  temperature  of  350°  or  400° 
centigrade  (about  660°  to  750°  Fahrenheit)  in  a  closed  vessel,  acquire, 
after  cooling,  the  property  of  dissolving  in  the  above  liquids,  and  consti- 
tute excellent  varnishes  without  any  loss  of  material. 
2d.  When  heated  as  above  mentioned  alone,  or  mixed  with  one  or  more 
of  the  liquids  named,  these  resins  dissolve  perfectly  in  them,  and  constitute 
new  and  very  fine  varnishes. 
3d.  Calcutta  copal  resin,  heated  in  this  manner,  with  one-third  of  its 
weight  of  boiled  linseed  oil,  and  three  quarters  of  its  weight  of  oil  of  tur- 
pentine, gives  at  once,  without  loss,  a  thick  varnish,  clear,  limpid,  of  a 
fine  color,  slightly  yellow,  quite  fit  for  carriages  and  the  most  delicate 
interior  and  exterior  house  painting. 
Resins,  then,  acquire  new  properties  under  the  joint  influence  of  heat 
and  pressure  :  the  latter  rises  as  high  as  twenty  atmospheres.  This  is  a 
difficulty  which  manufacturers  will  have  to  solve  in  order  to  transfer  this 
new  process  from  the  laboratory  to  the  manufactory, —  Chem.  and  Drug., 
Dec.  15,  1866,  from  Journal  de  Pharmacie. 
Silk  Collodion. — The  product  of  the  silkworm  has  been  reduced  again 
by  art,  to  the  raw  material  or  gum  from  which  the  insect  spins  its  dainty 
fibre.  A  Frenchman,  M.  Persoz,  fils,  makes  the  discovery,  using  chloride 
of  zinc  as  a  solvent  for  the  silk,  and  then  separating  the  silk  from  the 
solvent  by  Prof.  Graham's  dialysis.  This  is  a  very  simple  process  of  fil- 
tration. A  gutta-percha  vessel  with  a  parchment  bottom  receives  the 
solution  (diluted  with  water  to  the  consistency  of  collodion),  and  is  set 
upon  the  surface  of  water.  The  chloride  of  zinc  percolates  through  the 
moistened  parchment  bottom,  and  mixes  with  the  water;  leaving  the  pure 
fiberless  silk  substance  behind.  For  photographic  purposes,  it  is  iodized 
by  mixing  with  an  aqueous  solution  of  iodide,  and  then  dried  and  sensi- 
tized. The  chloride,  before  using,  is  heated  with  a  small  quantity  of  oxide 
of  zinc,  to  neutralize  any  excess  of  acid,  and  then  filtered  through  fine 
linen  to  remove  the  residuum  of  the  oxide.  For  a  prompt  solution,  the 
chloride  is  kept  warm.  The  separation,  to  be  entire,  occupies  a  few  days. 
— Drug.  Circ,  Feb.,  1867,  from  Scientific  American. 
Modified  Donovan's  Solution.  —  (Gazette  Hebdomadaire,  3  Aout, 
1866.)  The  formula  for  Donovan's  Solution  has  been  modified  in  various 
ways,  and  it  is,  perhaps,  in  part  due  to  this  circumstance  that  we  must 
attribute  the  want  of  uniformity  in  the  results  obtained  by  the  use  of  this 
preparation.    It  is  difficult  to  say  to  which  one  of  these  preparations  we 
