92 
Phenol  as  a  Test  for  Nitrites,  etc. 
Am.  Jour.  Pharm. 
Feb.,  1889. 
but  ferrous  sulphate  is  fatal,  so  that  with  1  drop  of  the  solution,  and 
hydrochloric  acid  10,000  N2Os  gives  no  reaction,  and  5000  is  very  in- 
distinct. 
Orcinol  and  nitrates : — The  remarks  which  apply  to  phenol  are 
mostly  true  of  orcinol,  but  with  the  addition  of  hydrochloric  acid  the 
latter  is  more  sensitive,  indicating  by  a  faint  pink  color  1  N205  in 
200,000  in  three  hours,  and  with  extreme  faintness  1  in  500,000.  The 
color  is  permanent,  and  orcinol  may  be  regarded  as  very  superior  to 
phenol  for  detecting  traces  of  nitrate  in  the  presence  of  large  quantities 
of  hydrochloric  acid  or  chlorides.  Ferric  chloride  is  objectionable, 
but  neither  sulphurous  acid  nor  ferrous  sulphate  interferes  with  the 
reaction,  whilst  copper  sulphate  makes  it  more  delicate  ;  500,000  N205 
with  hydrochloric  acid,  1  drop  of  copper  solution  and  2  drops  of 
orcinol  gives  sharp  bands  in  five  minutes. 
With  chlorates,  phenol  gives  a  pale  yellow  band  with  blue  below, 
the  latter  soon  fading  with  10,000  C1205 ;  with  4000,  the  blue  soon 
changes  to  dingy  green,  with  2000  the  blue  is  dingy  and  becomes 
dingy  green ;  with  1000  and  upwards  no  blue  is  developed.  Orcinol 
is  somewhat  more  delicate,  100,000  C1205  giving  a  faint  transient  blue 
band,  which  becomes  more  distinct  as  the  strength  of  the  solution  in- 
creases, so  that  with  10,000  C]205  a  beautiful  blue  band  is  produced, 
soon  acquiring  the  colors  of  the  rainbow,  4000  gives  a  similar  effect, 
but  not  so  good,  owing  to  interference  of  a  deep  green  coloration  :  1000 
gives  an  intense  green,  soon  turning  brown,  and  100  only  a  pale  yel- 
low. These  changes  are  not  observed  with  other  oxidizing  agents,  and 
therefore  this  may  possibly  become  a  characteristic  test  for  chloric 
acid.  Hydrochloric  and  sulphurous  acids  interfere  slightly  with  this 
reaction. 
These  reactions  have  been  applied  to  the  detection  of  nitrites, 
nitrates,  and  chlorates  in  the  presence  of  each  other,  and  the  author  has 
tested  this  point  by  various  mixtures  made  from  his  solutions.  With 
nitrites  and  nitrates  in  various  proportions  there  seems  to  be  no 
difficulty  in  detecting  them  both ;  the  nitrite  is  first  identified,  the 
mixture  is  then  treated  with  a  "drop  or  two  of  sulphurous  acid  to 
destroy  the  nitrite ;  to  ensure  the  complete  destruction  of  the  nitrite 
the  solution  of  the  mixture  should  be  acid  ;  it  is  then  tested  again  with 
hydrochloric  acid  and  orcinol,  or  if  great  delicacy  is  desired,  with  the 
addition  of  copper  sulphate,  when  mere  traces  of  nitrate  give  a  color- 
ation.   With  nitrites  and  chlorates,  the  red  coloration  with  phenol  and 
