EEDUCTION  OF  TEMPERATURE  BY  THE  SOLUTION  OF  SALTS.  425 
tion  when  kept  for  a  considerable  time  at  temperatures  higher 
than  the  melting  points  of  both  these  metals,  and  in  a  feeble 
current  of  pure  hydrogen  to  prevent  their  oxidation.  The  author 
has  made  some  of  these  experiments  on  a  very  large  scale,  hav- 
ing at  his  disposal  large  quantities — several  hundred  kilos. — of 
these  metals  in  pure  and  alloyed  state  ;  he  also  describes  an  in- 
genious pyrometer  devised  and  invented  by  him,  but  space  for- 
bids us  to  enter  into  further  details. — Chemical  News,  London, 
July  16,  1869. 
ON  THE  REDUCTION  OF  TEMPERATURE  BY  THE  SOLU- 
TION OF  SALTS. 
By  Fr.  Rudorff. 
The  reduction  of  temperature  which  takes  place  on  dissolving 
salts  must  be  the  greater  the  more  of  this  salt  is  dissolved  in  the 
water ;  and  the  maximum  of  the  reduction  must  be  reached  if 
salts  and  water  are  brought  together  in  such  a  proportion  that 
at  the  temperature  aimed  at  a  saturated  solution  is  obtained ; 
any  excess  of  water  or  salt  will  serve  only  to  prevent  the  solu- 
tion from  reaching  the  maximum' of  reduction,  since  the  excess 
has  to  be  cooled  down  likewise.  This  had  not  been  taken  into 
consideration  by  former  experimenters,  and  hence  the  dilference 
of  their  results. 
To  avoid  the  influence  of  the  surrounding  atmosphere,  the 
solution  must  be  efl'ected  as  quick  as  possible,  which  is  done  by 
using  the  salt  in  fine  powder,  and  in  slight  excess  over  the  quan- 
tity actually  necessary,  and  by  stirring  the  mixture. 
In  making  the  experiments  the  finely  powdered  salt  and  the 
requisite  quantity  of  water,  each  contained  in  thin  beaker  glasses, 
were  kept  from  12  to  18  hours  in  a  room  of  uniform  tempera- 
ture, so  that  both  had  exactly  the  temperature  of  the  room  ;  the 
water  was  then  added  to  the  salt  and  the  mixture  stirred  with  a 
good  thermometer ;.  the  greatest  reduction  took  place  within  one 
minute.  The  results  in  the  following  table  are  the  mean  of  sev- 
eral experiments,  which  never  differed  more  than  -2°  C.  from  each 
other: 
