420    ALTERATION  03?  FREEZING  POINT  IN  THERMOMETERS 
result  is  true  in  the  case  of  the  strongest  ammonia,  had  been 
previously  shown.    The  author  concluded  by  tracing  the  forma- 
tion of  pyrophosphoric  acid  in  stages,  as  follows  j— 
I.  PC15+H30=FCIS0+2HCI. 
ii  %  |  pcio  I   +HJt0  =  2HCl+^1^|a 
Pyrophosphoric  acid,  P2H4Or 
■*—Lond*  Ckem.  JVews,  June  28,  1867* 
OBSERVATIONS  ON  THE  ALTERATION  OP  THE  FREEZ- 
ING POINT  IN  THERMOMETERS. 
By  Br.  J.  P.  Joule,  F.R.S.,  V.F. 
Haying  had  in  my  possession,  and  in  frequent  use,  for  nearly 
a  quarter  of  a  century,  two  thermometers,  of  which  I  haTe, 
from  time  to  time,  talken  the  freezing  points,  I  thinfe  the  results 
may  offer  some  interest  to  the  Society.  Both  thermometers  are 
graduated  on  the  stem,  and  are,  I  believe,  the  first  in  this  coun- 
try which  were  accurately  calibrated.  Thirteen  divisions  of  one 
of  them  correspond  to  one  degree  Fahrenheit.  It  was  made  by 
Mr.  Dancer,  in  the  winter  of  1843—44.  My  first  observation 
of  its  freezing  point  was  made  in  April,  1844.  Calling  this 
&ero?  my  successive  observations  have  given 
0  April,  1844. 
5-  5  February,  1846. 
6-  6  January,  1848. 
6-9  April,  1848. 
8-  8  February,  185& 
9-  5  April,  1856. 
11-1  December,  18601 
11-8  March,  1867. 
The  total  rise  has  been,  therefore,  -91  of  a  degree  Fahrenheit* 
The  other  thermometer  is  not  so  sensitive,  having  less  than  four 
divisions  to  the  degree.  The  total  rise  of  its  freezing  point  has 
Ibeen  only  *6  of  a  degree  ;  but  this  is  probably  owing  to  the  time 
which  elapsed  between  its  construction  and>  the  first  observation 
