•CHROMIC  ACID  AND  THE  VOLATILE  OILS. 
197 
proportion  of  1  to  63,  and  from  which  on  cooling  it  is  precipitated 
in  fine  acicuiar  crystals. 
A  very  nice  and  efficient  cerate  I  have  prepared  by  digesting 
giv.  Pulv.  Ganth.  vittata  in  oil  of  turpentine  for  twenty  hours, 
then  transferring  to  a  percolator,  and  pouring  upon  it  boiling  oil 
of  turpentine  until  f.3vi  pass  through.  This  percolate  is  then, 
by  means  of  a  water  bath,  evaporated  to  about  one  eighth,,  and  to 
this  is  added  Cero3  Alboe  siiiss,  Adipis  5vi;  fused,  intimately 
rnixed,  and  continually  agitated  until  cold,  that  a  cerate  of  a 
homogeneous  consistency  may  be  obtained. 
As  a  means  of  protecting  cantharides  from  the  mite,  I  have 
found  none  more  efficient  than  oil  of  turpentine,  or  fragments  of 
white  turpentine  placed  amongst  them. 
From  the  extreme  hygroscopic  tendency  of  cantharides,  it  is 
highly  important  also,  as  a  means  of  preservation,  that  they 
should  especially,  when  in  powder,  be  kept  in  close  vessels  to  ex- 
clude moisture. 
To  neglect  or  ignorance  of  this  important  fact  is  to  be  attri- 
buted, in  many  cases,  the  too  frequent  deterioration  and  inferiority 
of  the  vesicating  fly. 
ON  THE  MUTUAL  ACTION  OF  CHROMIC  ACID  AND  THE 
VOLATILE  OILS. 
By  John  T.  Plummer,  M.  D. 
In  the  year  1848,  while  repeating  some  toxicological  experi- 
ments for  the  detection  of  strychnia,  I  observed  a  phenomenon, 
of  which  I  made  a  record  at  the  time,  but  did  not  institute  much 
inquiry  into  the  cause  of  it. 
I  had  mixed  together  in  a  glass  capsule  (not,  as  usual,  sulphuric 
acid  and  strychnia,  but)  sulphuric  acid  and  chromate  of  potassa ; 
and,  while  slowly  approximating  a  drop  of  a  very  weak  solution 
of  strychnia  in  alcohol,  on  the  end  of  a  glass  rod,  I  thought  I  per- 
ceived a  change  in  the  color  of  the  acid  mixture  nearest  the  drop, 
before  the  two  came  in  contact.  This  discovery  induced  me  to 
continue  the  drop  suspended  over  the  mixture  some  time  longer, 
until  I  became  convinced,  from  the  extension  of  the  discoloration, 
that  I  was  not  mistaken  in  my  observation. 
As  the  color  produced  was  not  red  but  green,  I  supposed  it 
