Am.  Jour.  Pharin. 
Feb.,  1892. 
Percentages  in  Solution. 
73 
tiply  4557  by  the  percentage  desired,  to  obtain  the  quantity  in 
grains  of  the  solid,  dissolve  in  a  small  quantity  of  the  solvent,  and 
then  add  sufficient  water  to  make  the  whole  weigh  ^^-J  grains.  In 
this  case,  also,  the  volume  will  be  slightly  less  than  a  fluidounce. 
When  it  is  stated  that  each  solid,  on  solution,  displaces  a  different 
volume  of  the  solvent  according  to  the  solid  dissolved,  it  will  be 
seen  that  to  obtain  exactly  a  fluidounce  or  a  pint  of  a  certain  per 
cent,  solution  of  a  compound,  there  must  be  taken  into  considera- 
tion the  relative  expansion  in  volume  of  each  solid ;  and  each 
solid  is  a  law  unto  itself.  Hence,  it  is  more  practical  to  take  the 
weight  of  a  fluidounce  or  a  pint  of  the  solvent,  as  ioo  per  cent, 
minus  the  per  cent,  solution  de.sired,  as  a  basis,  and  work  out  the 
quantity  desired  by  simple  proportion,  ignoring  the  increase  in  vol- 
ume, which  of  necessity  must  be  an  ever  variable  factor,  according  to 
the  compound  dissolved.  Say,  for  example,  that  one  wishes  to  make 
a  t-^q-q  or  a  yg^nr  or  a  ^^QQ  solution  of  bichloride  of  mercury,  the 
readiest  method  is  to  divide  7,291  by  1,000,  1,500  or  2?O0O  to  obtain 
the  number  of  grains  per  pint,  and  then  add  sufficient  water  to  make 
the  product  weigh  7,291  grains.  In  this  connection  it  may  be  of 
value  to  state  that  it  is  never  necessary  to  use  alcohol  in  making  the 
familiar  1  :  8  bichloride  of  mercury  solution  when  ammonium  chlo- 
ride is  also  ordered,  as  water  alone  is  sufficient  to  dissolve  mer- 
curic chloride  under  these  conditions.  In  the  absence  of  the 
ammonium  salt,  however,  alcohol  is  essential  for  solution. 
Concerning  the  1  :  20,  1  :  40,  or  1  :  60  carbolic  acid  solutions, 
these  terms  may  either  be  reduced  to  a  percentage  first,  and  the 
proper  quantity  of  the  acid  per  pint  obtained  by  multiplying  7,291 
by  the  percentage,  or  7,291  may  be  divided  by  20,  40  or  60,  as  the 
•case  may  be,  to  obtain'  the  number  of  grains  per  pint — in  both 
cases,  however,  making  up  to  7,291  grains  in  weight  by  the  addi- 
tion of  water.  If  a  gallon  of  the  solution  be  wished,  it  is  scarcely 
needful  to  say,  that  the  quantity  should  be  multiplied  by  eight, 
and  the  number  of  grains,  for  convenience  sake,  reduced  either  to 
troy  ounces  by  dividing  by  480,  or  to  avoirdupois  ounces  by  dividing 
by  437  5- 
When  it  becomes  necessary  to  use  a  liquid  other  than  water  as 
the  solvent,  a  seeming  difficulty  arises,  but  it  is  one  which  is  easily 
overcome.  In  such  a  case,  first  determine  the  weight  in  grains  of  a 
fluidounce    or  of  a  pint  of  the  dissolving  liquid  by  multiplying 
