ON  monsbl's  salt, 
203 
oxide  was  quite  violent,  but  by  dropping  in  the  acid  was  con- 
trolled. The  great  advantage  in  maintaining  the  temperature 
of  ebullition  is,  that  the  nitric  oxide  is  evolved  as  soon  as  it  is 
formed,  and  not  allowed  to  become  dissolved  in  the  solution 
from  which  it  is  afterwards  quite  difficult  to  be  thoroughly  separat- 
ed. A  few  minutes  boiling  at  the  end  of  the  process  was  sufficient 
to  render  free  from  odor  the  solutions  made  at  the  boiling  tem- 
perature ;  while  those  prepared  with  more  moderate  heat  had  to 
be  boiled  nearly  half  an  hour  before  they  were  brought  to  the 
same  condition. 
The  solutions  last  obtained,  as  well  as  scales  prepared  from 
them,  have  been  kept  more  than  a  month,  and  as  yet  no  changes 
have  occurred  in  them.  The  solutions  are  clear  and  odorless 
as  at  first,  and  the  scales  remain  transparent. 
The  scales  were  obtained  by  evaporating  the  solution  to  the 
consistence  of  honey,  spreading  it  thinly,  by  means  of  a  camel's 
hair  pencil,  on  glass  plates,  exposing  these  over  a  stove  to  a 
heat  of  180°  for  half  an  hour,  or  until  the  point  of  a  knife  press- 
ed upon  the  salt  showed  it  to  be  brittle,  by  causing  a  fracture. 
Then,  while  the  plates  were  warm,  pressing  a  knife  edge  upon 
the  salt  in  lines  about  the  eighth  of  an  inch  apart.  Separated  in 
this  way,  the  scales  were  about  as  large  as  those  of  citrate  of 
iron  usually  are.  They  were  deliquescent,  but  not  so  much  so 
as  I  expected  to  find  them.  I  think  they  are  exceeded  in  that 
respect  by  acetate  of  potassa. 
Care  should  be  taken  to  bottle  them  immediately  after  sepa- 
rating from  the  plates,  as  they  are  very  adhesive  and  trouble- 
some to  manage  after  tbey  have  deliquesced.  When  exposed  to 
a  heat  of  about  300Q,  100  grains  lost  22  grains  of  water ;  78 
grains  of  the  anhydrous  salt  being  left. 
In  a  dispensing  establishment,  it  is  advantageous  to  have  a  de- 
finite solution  of  the  salt  on  hand,  so  that  when  a  solution  is 
prescribed,  the  concentrated  one  can  be  properly  diluted,  in- 
stead of  dissolving  the  salt  in  scales  or  that  in  the  anhydrous 
form  ;  the  former  being  more  valuable  on  account  of  the  time 
and  trouble  necessary  to  its  preparation  ;  the  latter  being  so 
slowly  soluble. 
To  obtain  such  a  solution,  that  resulting  from  the  process 
before  given  may  be  taken.    By  calculation  it  is  found  to  con- 
