8 
CALCINED  MAGNESIA. 
if  it  had  been  calcined  without  this  addition,  and  should  it  con- 
tain a  small  amount  of  lime,  this  will  have  become  a  chloride, 
and  it  will  consequently  be  less  caustic. 
Husband's  calcined  magnesia,  the  most  popular  of  the  imita- 
tions of  Henry's,  is,  like  the  latter,  not  a  pure  magnesia,  but 
differs  from  it  in  containing  water  and  an  organic  salt.  If  it  be 
washed  with  distilled  water  it  will  be  found  to  have  the  ordinary 
taste  of  good  magnesia,  while  the  water  will  have  a  pleasant 
saline  taste,  and  will  exhibit  with  chemical  reagents  the  charac- 
teristics of  a  citrate.  The  amount  of  this  salt  contained  in  it  is 
not  uniform,  but  from  an  ordinary  sample  about  two  and  a  half 
per  cent,  of  soluble  salts  may  be  obtained  by  washing  and  evapo- 
ration. Besides  several  incidental  and  confirmatory  tests,  the 
principal  ones  upon  which  I  relied  were,  precipitating  the  solution 
(obtained  by  washing  the  magnesia  with  water)  with  acetate  of 
lead,  and  finding  the  precipitate  soluble  in  ammonia  ;  and  com- 
parative tests  with  solution  of  sulphate  of  soda,  and  sulphate, 
hydrochlorate  and  citrate  of  magnesia.* 
Trenton,  N.  J.,  Dec.  7  th,  1855. 
*  [At  the  request  of  the  author  we  washed  a  portion  of  Husband's  mag- 
nesia, and  obtained  but  six-tenths  of  one  per  cent,  of  soluble  matter  on 
evaporating  the  washings.  A  portion  of  this,  was  dissolved  in  water  and  the 
precipitate  by  acetate  of  lead,  not  in  excess,  was  found  to  re-dissolve  on  the  ad- 
dition of  liquor  ammonia,  or  a  solution  of  citrate  of  potassa ;  and  when  another 
portion  of  the  salt  is  heated  to  redness  in  a  tube,  covered  with  a  little 
ordinary  magnesia,  to  exclude  the  air,  it  is  at  once  blackened,  indicative  of 
organic  matter.  Whether  this  is  citric  acid,  as  believed  by  the  author, 
whether  it  is  an  accidental  contamination,  or  an  intentional  addition,  with 
a  view  to  modifying  the  taste  and  smoothness  of  the  earth,  we  did  not 
pursue  our  experiments  far  enough  to  determine,  but  in  cither  case  its 
presence  is  medically  unimportant,  unless  existing  in  larger  proportion  than 
our  experiments  indicate.  There  is  a  feature  of  this  magnesia,  however, 
which  deserves  attention  whenever  Husband's  magnesia  is,  by  the  physician 
or  apothecary,  used  with  a  view  to  its  basic  power,  and  that  is  the  fact  of 
its  being  a  partial  hydrate,  a  fact  which  has  been  shown  before.  (See  vol. 
xxii.  page  383,  and  vol.  xxiv.  page  199  of  this  Journal.)  In  the  trial  made 
at  this  time,  100  grains  taken  from  a  closed  bottle  lest  11  grains  by  expo- 
sure to  a  red  heat  for  twenty  minutes. — Ed.  Amer.  Jour.  Pharm.] 
