^No^!'i;mi!''''}     Supersaturated  Saline  Solutions,  etc.  507 
sulphate  in  eight  measures  of  syrup,  which  I  find  more  convenient 
for  general  dispensing,  but  it  contains  too  much  sugar  for  the  mist, 
ferri  co.  as  directed  in  the  present  edition  of  the  Pharmacopoeia. — 
Pharm.  Journ.  and  Trans.,  Sept.  2,  1871. 
ON  THE  BEHAVIOR  OF  SUPERSATURATED  SALINE  SOLUTIONS 
WHEN  EXPOSED  TO  THE  OPEN  AIR  * 
By  Charles  Tomlinson,  F.R.S. 
It  is  known  that,  when  a  vessel  containing  a  supersaturated  saline 
solution  is  opened  in  a  room,  it  immediately  crystallizes,  provided 
the  tempertaure  be  not  too  high.  Mr.  Tomlinson  shows  that  super- 
saturated solutions  of  Glauber's  salt  (and  also  of  Epsom  salt,  and  of 
alum)  may  be  exposed  to  the  open  air  of  the  country  for  many  hours, 
and  even  be  taken  out  of  the  flasks  in  clean  metal  spoons,  without 
crystallizing.  From  a  large  number  of  experiments,  conducted  under 
various  conditions,  the  following  conclusions  are  drawn : — 
1.  That  a  highly  supersaturated  solution  of  sodic  sulphate  may 
be  exposed  to  the  open  air  of  the  country  in  an  uncovered  flask,  and 
in  cloudy  weather,  for  from  twelve  to  twenty  hours,  without  any 
formation  of  the  ordinary  ten-watered  salt. 
2.  That  if  the  temperature  fall  to  40°F.,  and  under,  the  modified 
seven-atom  salt  is  formed  at  the  bottom  of  the  solution,  just  as  in 
covered  vessels. 
3.  That  if  the  exposed  solution  suddenly  crystallizes  into  a  com- 
pact mass  of  needles,  a  nucleus  may  always  be  found  in  the  form  of 
an  insect,  a  speck  of  soot,  a  black  point  of  carbon,  &c. 
4.  That  if,  during  the  exposure,  rain  come  on,  the  solution  gen- 
erally crystallises  suddenly,  in  consequence  of  an  active  nucleus  being 
brought  down.  But  if  the  flask  be  put  out  during  heavy  rain,  when 
we  may  suppose  all  the  solid  nuclei  to  have  been  brought  down,  the 
rain-drops,  now  quite  clean,  fall  into  the  solution  without  any  nuclear 
action. 
5.  That  the  young  and  newly-sprouted  leaves  of  trees,  such  as 
the  gooseberry  and  current  bushes,  have  no  nuclear  action. 
6.  That,  in  clear  cloudless  weather,  when  the  force  of  evaporation 
is  strong,  the  solutions,  by  exposure,  produce  fine  groups  of  crystals 
*Read  before  the  British  Association,  Edinburgh  Meeting,  Section  B. 
