346  Gleanings  from  the  German  Journals.  {Am"jSy%£iarm' 
Test  papers. — E.  Dieterich  made  a  series  of  test  papers  by 
impregnating  filtering  paper  with  solutions  (i  :  250)  of  the  following 
salts :  Potassium  ferrocyanide,  this  will  indicate  one  part  ferric 
chloride  in  25,000  parts  of  water  and  one  part  copper  sulphate  in 
2,000  parts  of  water ;  Potassium  ferri-cyanide  which  will  indicate 
one  part  of  ferrous  sulphate  in  40,000  parts  of  water ;  Potassium 
sulpliocyanate  will  react  with  ferric  chloride  1  :  5,000;  Potassium 
iodide  will  indicate  lead  acetate  1  :  500,  bismuth  nitrate  1  :  7,000  and 
silver  nitrate  1  :  1 ,000  ;  Potassium  chr ornate  will  serve  to  detect  lead 
acetate  1  :  2,000  and  silver  nitrate  1  :  3,000;  Zinc  sulphide  (made  by 
coating  filtering  paper  with  freshly  precipitated  and  thoroughly 
washed  zinc  sulphide  suspended  in  water),  this  will  react  with  solu- 
tions containing  copper  sulphate  I  :  15,000,  lead  acetate  1  :  15,000, 
bismuth  nitrate  1  :  7,000,  silver  nitrate  1  :  8,000  and  mercuric  chloride 
I  :  1,200.  Starch  paper  can  be  made  to  indicate  one  part  iodine  in 
25,000  parts  water  ;  potassium  iodide  paper  one  part  chlorine  in 
30,000  parts  water  ;  litmus  paper  was  found  to  be  more  'delicate 
and  reliable  than  lacmoid  paper. — Pharm.  Centralhalle,  1891,  314. 
Purification  of  chemicals  by  great  cold. — Prof.  Pictet  who  about 
a  year  ago  moved  his  laboratory  from  Geneva  to  Berlin,  has  since 
been  engaged  in  experiments  having  for  their  object  the  elimination 
of  impurities  from  chemicals  by  the  aid  of  low  temperatures.  The 
first  source  of  cold  is  a  mixture  of  liquefied  carbonic  and  sulphurous 
oxides  (obtained  by  heating  strong  sulphuric  acid  with  carbon);  this,  if 
under  a  pressure  of  4— 12  atmospheres,  will  produce  sufficient  cold  on 
evaporation  to  liquefy  nitrogen  monoxide  ;  the  latter  under  a  pressure 
of  200-400  atmospheres  will  liquefy  air,  hydrogen,  oxygen  and  nitro- 
gen. The  experiments  made  upon  the  purification  of  chloroform 
are  very  interesting :  The  purest  chloroform  of  commerce  subjected 
to  a  cold  of  — 700  C.  deposits  a  crystalline  body,  which  is  removed 
and  the  liquid  portion  subjected  to  a  temperature  below  — ioo°  C, 
when  the  chloroform  separates  in  crystals  and  is  freed  from  a 
liquid  portion.  The  chloroform  purified  by  this  treatment  does  not 
impart  any  color  to  sulphuric  acid  although  they  may  be  in  contact 
for  a  long  time ;  chromic  acid  mixture  (bichromate  of  potassium 
solution  and  concentrated  sulphuric  acid)  is  reduced  by  the  best  com- 
mercial samples,  while  the  chloroform  purified  by  cold  is  unaffected; 
exposure  to  light  for  a  long  time  without  the  addition  of  alcohol 
does  not  appear  to  induce  decomposition.    It  has  been  suggested 
