674 
Current  Literature. 
Am.  Jour.  Pharm. 
Sept.,  19 18. 
ficulties;  any  strong  bleaching  agent,  if  present,  must  first  be  re- 
moved. The  test  should  not  be  performed  on  a  borosilicate  glass 
slide.  The  test  is  only  valid  for  free  boric  acid ;  without  the  addi- 
tion of  mineral  acid,  borates  do  not  respond.  The  test  is  sensitive 
to  1  drop  of  a  N/i 0,000  solution  of  boric  acid;  1  drop  of  a  solution 
containing  0.000025  Mgm.  of  boron  gives  a  positive  result. 
The  Detection  of  the  Heavy  Metals  by  Means  of  Zinc 
Sulphide  Wool  Fibers. — Several  natural  and  artificial  fibers  were 
tested  as  a  vehicle  for  zinc  sulphide,  but  the  only  fibers  which  could 
be  caused  to  absorb  sufficient  of  the  reagent  for  satisfactory  use 
were  wool  and  mohair.  The  preliminary  treatment  of  the  wool 
fiber  is  important.  The  fat  is  removed  by  treatment  with  a  mixture 
of  alcohol  and  ether;  the  fiber  is  then  swelled  by  soaking  overnight 
at  the  room  temperature  in  1  per  cent,  sodium  hydroxide  solution. 
It  is  then  washed  and  dipped  five  or  six  times  alternately  in  solu- 
tions of  10  per  cent,  zinc  acetate  and  10  per  cent,  sodium  sulphide 
the  excess  liquid  being  pressed  out  each  time  but  not  washed. 
After  the  final  dipping  the  impregnated  wool  is  washed  and  dried 
by  pressing  between  filter-papers.  The  sodium  sulphide  solution  is 
prepared  by  passing  sulphuretted  hydrogen  into  sodium1  hydroxide 
until.no  precipitate  is  formed  with  magnesium  chloride.  To  apply 
the  test,  a  drop  of  the  solution  to  be  tested  is  placed  on  a  glass  slide 
and  a  drop  of  dilute  hydrochloric  acid  is  added.  A  piece  of  .the 
treated  fiber  about  5  Mm.  long  is  introduced  and  examined  under 
the  microscope.  The  liquid  is  evaporated  to  dryness,  a  drop  of 
dilute  ammonia  solution  is  added,  and  the  fiber  again  examined  side 
by  side  with  a  new  fiber  for  detecting  slight  differences  of  color  by 
comparison.  The  color  changes  are  yellow,  orange,  brown,  or  black. 
In  acid  solution  the  indications  are  :  Straw-yellow,  tin ;  lemon-yellow, 
arsenic  or  cadmium ;  orange,  antimony ;  reddish-brown,  bismuth ; 
brown  or  yellow-brown,  platinum,  copper,  mercury,  antimony  (some- 
times cobalt,  iron,  manganese  or  nickel)  ;  black  or  brown  in  very 
dilute  solution,  silver,  lead  gold,  mercury.  With  no  color  in  acid 
solution  the  fiber  may  turn  brown  or  yellow-brown  in  alkaline  solu- 
tion in  presence  of  cobalt,  iron,  manganese  or  nickel,  but  these  ele- 
ments rarely  give  good  reactions.  Since  the  fiber  is  viewed  in  trans- 
mitted light,  a  heavy  precipitate  of  yellow  or  orange  color  may  ap- 
pear brown  or  black  owing  to  its  density;  conversely,  a  brown  or 
