CLEANING  AND  PRESERVATION  OF  ENGRAVINGS.  397 
stance  capable  of  alteration,  gas  is  produced.  In  most  cases 
these  gases  are  hydrogen,  marsh  gas,  or  carbonic  oxide ;  they 
are  entirely  formed  of  hydrogen  and  carbonic  oxide  if  the 
foreign  substance  is  wood  spirit.  This  reaction  occurs  in  the 
cold  and  nearly  instantaneously. — Rep.  de  Pharm.,  Av.,  1862. 
Opium  altered  by  age.— In  his  memoir  on  opium,  M.  Gui- 
bourt  states,  that  in  analysing  an  opium  kept  in  his  store  nearly 
twenty  years,  he  obtained  less  morphia  than  he  had  extracted 
from  the  same  opium  when  recent.  The  product  obtained  was 
strongly  colored,  and  the  alcoholic  solution  equally  so.  The 
extractive  matter,  (says  the  professor,)  and  other  principles  with- 
out doubt,  the  morphia,  perhaps,  is  converted  into  a  brown  body 
(apotheme  ?)  little  soluble  in  water,  but  soluble  in  alcohol  like 
morphia,  and  precipitating  with  it  by  the  cooling  of  the  liquid, 
and  can  only  be  separated  by  combining  the  alkaloid  with  an 
acid,  and  decolorizing  the  salt  by  charcoal,  &c. — Rep.  de  Pharm. 
Avril,  1862. 
ON  THE  CLEANING  AND  PRESERVATION  OF  ENGRAVINGS, 
Augustus  A.  Hayes,  M.  D.,  State  Assayer  of  Massachusetts, 
says  in  the  Scientific  American  : — 
The  frequent  inquiries  addressed  to  me  by  those  who  possess 
valuable  engravings — which  have  become  damaged  through  ac- 
cident or  exposure — respecting  a  mode  I  adopted  successfully 
for  restoring  some  very  fine  ones,  induce  me  to  publish  a  gene- 
ral process  applicable  to  the  largest  number  of  cases. 
Any  one  who  will  incur  the  trouble  of  looking  up  in  the 
older  print-shops  and  depositories  in  residences  in  this  country, 
will  find  abundance  of  defaced  engravings  of  rare  merit,  the 
works  of  the  best  masters  rejected,  which  can  be  restored  easily 
to  quite  their  former  degree  of  freshness  and  beauty.  All  who 
have  studied  the  better  efforts  of  the  old  artists  in  giving  per- 
manency to  their  conceptions  in  this  department  of  art,  assign 
to  it  a  very  high  place,  and  it  may  be  suggested  that  a  higher 
cultivation  and  enjoyment  of  design  and  execution,  in  so  far  as 
the  influences  of  light  are  concerned,  may  be  gained  from  care- 
ful observations  of  engravings  than  can  result  from  time  be- 
