350        NEW  METHOD  FOR  DETECTING  SULPHUR  IN  HOPS. 
sulphur  for  any  dishonest  purpose,  as  seems  to  be  the  opinion  in 
North  Germany,  but  merely  to  improve  their  keeping  qualities, 
and  render  them  more  fit  for  exportation. 
The  author  has  tried  the  method  proposed  by  Dr.  Heidenreich, 
of  Ansbach  upwards  of  three  years  years  ago,  and  employed  it 
in  numerous  instances  in  judicial  proceedings.  According  to 
this,  twenty  or  thirty  of  the  cones  of  the  hop  are  placed  in  a 
flask  with  zinc  and  muriatic  acid,  and  the  hydrogen  evolved 
passed  through  a  solution  of  acetate  of  lead  ;  if  the  hops  con- 
tained sulphurous  acid,  sulphuretted  hydrogen  is  produced,  and 
causes  a  dark  brown  precipitate  of  sulphuret  of  lead. 
This  process  is  satisfactory  when  the  hops  have  been  sulphured 
within  a  few  (three  to  four)  weeks,  but  is  not  sufficiently  delicate 
when  the  object  is  to  detect  a  minute  trace  of  sulphur. 
The  author  has  effected  an  improvement  on  Heidenreich's 
method.  It  now  affords  us  a  means  of  detecting  sulphurous 
acid,  not  only  in  hops,  but  also  in  all  other  substances,  such  as 
wines,  bleached  silk,  &c,  even  when  it  exists  in  such  minute 
quantity  as  to  escape  detection  by  any  other  method. 
The  test  is  founded  on  the  fact,  that  a  solution  of  nitroprus- 
side  of  sodium  is  colored  a  magnificent  purple  by  the  smallest 
trace  of  an  alkaline  sulphuret,  such  as  sulphuret  of  potassium  or 
ammonium. 
In  the  employment  of  the  test,  a  solution  of  nitroprusside  of 
sodium,  so  dilute  as  to  appear  of  a  very  light  brown  color,  is 
placed  in  a  beaker,  and  a  few  drops  of  solution  of  caustic  potash 
added.  The  process  is  now  conducted  as  in  Heidenreich's  me- 
thod. The  hops  under  examination  are  placed  in  a  flask  with  a 
piece  of  sheet  zinc,  diluted  muriatic  acid  poured  over  them,  and 
the  gas  conducted  into  the  solution  of  the  nitroprusside.  If  the 
gas  contain  but  a  minimum  of  sulphuretted  hydrogen,  the  first 
bubble  causes  a  violet  cloud  in  the  solution ;  after  passing  the 
gas  for  a  short  time,  it  assumes  the  magnificent  color  of  the  so- 
lution of  permanganate  of  potash.  The  vapor  of  muriatic  acid 
passing  over  with  the  gas,  does  not  affect  the  reaction  unless  it 
be  continued  too  long.  It  will  be  readily  understood  that  the 
gas  should  not  be  washed  ;  at  most  it  should  be  filtered  through 
cotton-wool. 
