408  General  Method  of  Chemical  Synthesis.  { Ami™r,  Sarm- 
chiefly  due  to  the  circumstance  that  in  the  gravimetric  method  the 
milk  is  weighed,  whilst  in  the  new  method  it  is  measured,  and  that 
the  recalculation  may  occasion  errors. — Zeitschrift  f.  Anal.  Chemie, 
xxxv,  p.  168,  from  Chem.  News,  1893,  2%l- 
ATTEMPT  AT  A  GENERAL    METHOD  OF  CHEMICAL 
SYNTHESIS. 
By  Raoul  Pictet. 
In  order  to  develop  from  the  totality  of  facts  explained  in  my 
former  papers  a  practical  method  of  utilizing  low  temperatures  in 
chemical  syntheses,  it  will  be  useful  to  recall  the  partial  laws  which 
we  have  already  seen. 
The  fundamental  hypothesis  which  has  guided  us  and  the  experi- 
mental verifications  have  enabled  us  to  establish  eight  laws : 
(1)  At  very  low  temperatures,  below  — 13c0,  no  chemical  reaction 
takes  place,  whatever  substances  are  present. 
(2)  All  chemical  reactions  are  manifested  spontaneously  at  a  cer- 
tain temperature  and  under  a  certain  pressure  exerted  upon  the  con- 
stituents ;  this  is  the  temperature  limit. 
(3)  The  same  reactions  may  be  obtained  below  the  temperature 
limit  if  we  apply  auxiliary  energy  by  the  use  of  electric  currents  or 
discharges. 
(4)  Exothermic  reactions  always  present  two  phases:  in  the  for- 
mer we  retain  a  control  of  the  temperatures  if  we  can  remove  from 
the  combining  bodies,  by  radiation  as  much  heat  as  is  produced  at 
the  same  moment  by  the  simultaneous  effect  of  the  affinities  of  the 
extraneous  energies  introduced  into  the  substances.  In  the  second 
phase,  the  temperature  rises  suddenly  until  the  reaction  takes  place 
above  the  temperature  limit. 
The  first  phase  is  the  reaction  limit.  The  second  phase  is  the 
reaction  in  mass. 
(5)  Endothermic  reactions  are  always  limit  reactions. 
(6)  The  dissociation  of  the  products  obtained  by  exothermic 
reactions  corresponds  to  the  laws  of  endothermic  combinations  and 
reciprocally. 
(7)  The  temperature  limit  of  chemical  reactions  is  not  in  a  known 
simple  relation  with  the  apparent  energy  of  the  phenomenon.  On 
the  contrary,  the  quantities  of  heat  liberated  seem  to  class  the 
