NITROPRUSSIDES,  THEIR  COMPOSITION  AND  MANUFACTURE.  233 
These  tests  will  show  whether  tar  oils  have  been  used  as 
adulterants  ;  but  to  ascertain  whether  the  liquid  consists  of  a 
mere  solution  of  carbolic  acid  in  water  or  alkali,  or  whether  it 
contains  sulpho-carbolic  or  sulpho-cresylic  acids,  another  test 
must  be  used,  based  upon  the  solubility  of  these,  and  the  insolu- 
bility of  carbolic  acid,  in  a  small  quantity  of  water.  In  this 
case  proceed  as  follows  : — 2.  Put  a  wine-glassful  of  the  liquid  to 
be  tested  in  a  bottle,  and  pour  on  it  half  a  pint  of  warm  water. 
If  the  greater  part  dissolves,  it  is  an  adulterated  article.  Test 
the  liquid  in  the  bottle  with  litmus  paper;  if  strongly  acid  it 
will  show  the  probable  presence  of  sulpho-acids,  whilst  if  alka- 
line it  will  show  that  caustic  soda  has  been  probably  used  as  a 
solvent. 
These  tests  are  not  given  as  having  any  pretensions  to  scien- 
tific accuracy,  but  as  affording  persons  who  are  desirous  of  using 
carbolic  acid,  and  are  willing  to  pay  a  fair  price,  a  rough  and 
ready  means  of  seeing  if  they  are  being  imposed  upon. 
If  greater  accuracy  in  the  tests  are  required,  recourse  should 
also  be  had  to  distillation  with  a  thermometer — carbolic  acid 
boils  at  184°  C,  cresylic  at  203°  C,  whilst  xylic  acid  (96), 
which  may  possibly  be  present,  and  has  great  antiseptic  value, 
boils  at  220°  C.  Eeichenbach's  pure  creosote  (33)  boils  at 
219°  C. 
(To  be  continued.) 
NITROPRUSSIDES,  THEIR  COMPOSITION  AND  MANU- 
FACTURE. 
Some  doubt  has  always  been  attached  to  the  composition  of 
the  nitroprussides  since  their  discovery  by  Playfair.  Some  re- 
cent researches,  however,  by  E.  A.  Hadow,  which  are  remark- 
able for  the  skill  and  ability  they  display,  have  removed  all  uncer- 
tainty in  the  matter,  and  have  given  us  a  clear  insight  into  the 
formula  for  this  interesting  class  of  salts.  Mr.  Hadow  started 
from  the  assumption  that  the  nitroprussides  are  formed  from  the 
ferridcyanides,  by  the  displacement  of  an  atom  of  alkaline 
cyanide  by  one  of  the  oxides  of  nitrogen.    Thus  : — 
