264  RELATIVE  FUEL  VALUE  OF  ALCOHOL  AND  WOOD-SPIRIT. 
The  red  dye  cake  was,  therefore,  nothing  else  than  a  cake  of 
cochineal  insects,  collected  when  the  females  were  full  of  ova, 
but  also  containing  others  in  which  the  ova  had  become  developed, 
and  escaped  from  the  mother-cell  or  insect.  This  latter  fact  at 
once  accounted  for  its  inferiority  to  cochineal  itself  as  a  color- 
producing  agent.  It  is  a  well-known  fact,  relative  to  the  whole 
of  the  insects  which  furnish  cochineal,  lac,  and  kermes,that  the 
largest  quantity  of  coloring  matter  is  yielded  by  the  mother  in- 
sect before  the  eggs  are  fully  developed,  and  that  little  coloring 
matter  is  yielded  by  those  in  which  the  eggs  are  fully  developed 
or  are  hatched.  As  this  cake  cochineal  contained  a  considera- 
ble proportion  of  females  in  which  the  ova  were  arrived  at  their 
full  development,  and  several  were  even  hatched,  this  satisfacto- 
rily accounted  for  the  smaller  proportion  of  coloring  matter 
which  the  cake  yielded. 
We  are  informed  that  this  cake  cochineal — for  so,  I  think,  it 
may  be  safely  termed,  cost  in  Cordova  from  4d.  to  9d.  the  ounce  ; 
that  is,  from  5s.  4c2.  to  12s.  the  pound.  As  the  best  cochineal 
can  be  bought  here  for  about  4s.  the  pound,  this  fact  at  once  set- 
tles the  question  as  to  the  profitable  introduction  of  this  red  cake 
to  this  country  as  an  article  of  commerce. 
After  the  above  details  it  is  unnecessary  to  say  that  this  sub- 
stance is  not  a  gum,  nor  an  exudation  from  a  prickly  pear  (or 
cactus)  as  Mr.  Black  has  been  informed  it  was  by  the  native  col- 
lectors. Had  it  been  so,  it  would  probably  have  been  a  new 
dye-stuff,  and  might  have  proved  of  much  value  to  commerce. 
As  it  is,  I  think  this  Society  will  agree  with  me,  that  Mr.  Black 
deserves  the  thanks  of  the  mercantile  public  for  bringing  under 
their  notice  a  dye  stuff  which  might  have  been  both  new  and 
valuable  London  Pharm.  Jour.  Feb.  1855. 
RELATIVE  FUEL-VALUE  OF  ALCOHOL  AND  WOOD-SPIRIT. 
Bolley  has  made  some  comparative  experiments  to  ascertain 
this  point. 
The  wood-spirit  used  was  slightly  yellow  and  empyreumatic  ; 
the  density  was  0.81 ;  it  began  to  boil  at  154°-4  F.,  and  then  the 
boiling-point  rose  gradually.    It  had  a  slight  acid  reaction,  and 
