CALCINED  MAGNESIA.  7 
recipe,  which  will  give  a  uniform  strength  to  the  solution,  and 
requires  only  our  officinal  acid,  (sp.  gr.  1.42,)  instead  of  the 
stronger,  which  it  is  always  difficult  to  procure. 
P.  Hydrargyrum,  *i  (Troy.) 
Acid,  nitric,  (sp.  gr.  1.42)  f.  ^ii. 
Aqua  dest.  f.  ^iss. 
In  the  acid  diluted  with  the  water,  dissolve  the  mercury  with 
the  application  of  heat,  and  evaporate  to  two  fluidounces. 
This  recipe  will  be  found  to  give  the  proper  proportion  of  acid, 
or  nearly  10  equivalents  of  acid  to  three  of  mercury  ;  our  nitric 
acid  of  the  sp.  gr.  1.42  is  a  quadrahydrated  acid,  represented 
thus,  N05  -f  4HO,  then  in  numbers 
SHg  =3  (101  =  303,)  and  10  (N05  +  4HO)  = 
10  (54+36)=  900. 
303  parts  of  mercury  require  900  parts  acid, 
one  ounce,  480  grains  of  mercury  gives  the  proportion, 
303  :  900  ::  480  :  1426.  grains  weight  of  acid  required, 
which  is  nearly  three  ounces,  troy. 
A  fluidounce  of  water  weighs  455.69  grains,  consequently, 
/1426\ 
4a '  —  two  fluidounces  and  a  fifth. 
455.(59 
The  importance  of  this  preparation  to  the  medical  profession 
renders  it  desirable  that  a  uniform,  correct  recipe  should  be 
adopted  for  its  preparation. 
Cynthiana,  Kentucky,  Oct.  2d,  1855. 
CALCINED  MAGNESIA. 
By  J.  B.  James,  M.  D. 
Pure  calcined  magnesia,  however  prepared,  has  a  taste  some- 
what resembling  lime,  and  this  taste  is  not  removed  either  by 
allowing  it  to  absorb  water  from  the  atmosphere,  or  by  suspending 
it  in  water. 
If  a  fine,  soft  carbonate  be  pulverized  and  calcined  at  a  low 
red  heat,  a  small  proportion  of  chloride  of  ammonium,  chloride 
of  magnesium,  or  hydrochloric  acid  having  been  previously  mix^d 
with  a  portion  of  it,  and  placed  at  the  bottom  of  the  vessel  in 
which  it  is  to  be  calcined,  the  product  will  be  more  compact  than 
