712 
Dissolving  Zinc  Chloride. 
Am.  Jour.  Pharra. 
Oct.,  1918. 
The  liquid  was  evaporated  upon  the  water  bath  to  nearly  con- 
stant weight.  It  was  now  in  the  form  of  a  thick  syrupy  liquid ; 
for  zinc  chloride  cannot  readily  be  dried  on  a  water  bath  under  at- 
mospheric pressure.  Besides  what  moisture  it  retains  this  syrupy 
residue  would  be  expected  to  also  contain  the  hydrochloric  acid  from 
the  reaction  producing  the  oxychloride  from  which  it  had  been 
filtered ;  later  it  will  be  shown  that  it  does  contain  this  hydrochloric 
acid. 
Two  series  of  experiments,  with  this  syrupy  residue,  were  ar- 
ranged. In  the  first  of  these  it  was  mixed  with  water  gradually 
added  and  finally  increased  to  a  considerable  bulk  to  find  that  it  dis- 
solved clear  throughout.  It  was  then  re-evaporated  under  the  same 
condition  to  a  syrupy  consistency  and  again  found  to  dissolve  clear ; 
a  third  such  treatment  was  given  it,  and  a  third  time  it  dissolved 
clear.  The  reason  for  its  doing  so  was  the  presence  of  a  sufficient 
amount  of  hydrochloric  acid,  tenaciously  retained  throughout  the 
evaporation,  to  effect  solution,  as  was  proven  to  be  the  case  by 
treating  the  syrupy  liquid  of  the  second  series  of  experiments  with 
zinc  carbonate.  When  put  into  the  syrupy  liquid  the  zinc  carbonate 
made  no  demonstration  of  the  presence  of  acid  until  the  mixture 
was  thinned  with  just  sufficient  water  to  permit  of  enough  motion 
for  reaction.  Effervescence  then  took  place  with  the  disappearance 
of  the  small  amount  of  zinc  carbonate  which  had  been  added.  More 
zinc  carbonate  was  now  added  until  in  excess,  and  the  solution 
warmed,  gradually  but  abundantly  diluted  with  water,  and  filtered. 
The  clear  liquid  would  now  be  considered  as  containing  no  free 
hydrochloric  acid.  Next,  it  was  evaporated  to  a  syrupy  consistency 
on  a  water  bath,  and  then  mixed  with  water,  as  had  been  done  in  the 
experiment  just  preceding  it.  Instead  of  dissolving  clear  as  the  pre- 
ceding one,  the  present  experiment  gave  with  first  portion  of  water 
a  clear  solution  but  upon  further  dilution  an  abundant  residue  of 
oxychloride.  This  was  separated  and  the  filtrate  evaporated  as  be- 
fore, and  upon  treatment  with  water  gave  a  clear  solution,  thus 
showing  that  the  acid  which  was  produced  in  the  solution,  along 
with  the  oxychloride,  was  sufficient  to  redissolve  all  of  the  zinc 
chloride.  Another  evaporation  and  solution  substantiated  this  opin- 
ion. The  liquid  of  the  first  series  was  now  evaporated  for  the 
fourth  time,  and  after  it  had  reached  the  syrupy  consistence,  the 
vessel  was  placed  over  a  direct  flame,  and  the  heat  continued,  while 
tests  were  made  from  time  to  time,  by  removing  a  drop  with  a  glass 
