Tests  for  Carbolic  Acid,  etc. 
{Am.  Jour.  Pharm. 
Jan.,  1879. 
water  absorbed  amounted  to  13  per  cent,  of  the  hydrated  acid.  On 
repetition  the  product  contained  14  per  cent. 
C7HgO,  H20  requires  12*7  per  cent,  of  water. 
In  the  subsequent  experiments,  when  mention  is  made  of  hydrous 
carbolic  or  cresylic  acid,  the  products  obtained  as  above  are  to  be 
understood. 
1.  Action  of  Cold. — Absolute  carbolic  acid  is  solid  at  ordinary  tem- 
peratures, and  the  hydrous  substance  solidifies  in  a  freezing  mixture  of 
hydrochloric  acid  and  crystallized  sulphate  of  sodium.  Neither  abso- 
lute nor  hydrous  cresylic  acid,  nor  creasote,  shows  any  signs  of  freezing 
on  exposure  to  the  same  degree  of  cold. 
2.  Solubility  in  Water. — Twenty  cc.  of  water  at  about  I70°C,  dis- 
solved 1 '8  cc.  of  hydrous  carbolic  acid.  This  corresponds  to  a  solu- 
bility of  1  volume  in  ii'i  of  water.  Hence  the  saturated  aqueous 
solution  contains  8*56  per  cent,  by  weight  of  the  absolute  acid,  corres- 
ponding to  a  solubility  of  one  part  by  weight  of  absolute  acid  in  10*7 
parts  of  water.  This  is  a  far  greater  solubility  than  is  generally  attrib- 
uted to  carbolic  acid,  the  discrepancy  being  probably  due  to  an  impure 
acid  being  generally  used.  In  hot  water  carbolic  acid  is  still  more 
soluble. 
Hydrous  cresylic  acid  dissolves  in  about  29  measures  of  water  at 
about  20°C,  which  represents  a  solubility  of  1  part  by  weight  of  abso- 
lute cresylic  acid  in  about  31  parts  of  water. 
3.  Solubility  at  i5*5°(C=6o0F.)  in  solution  of  Caustic  Soda  containing  61 
per  cent,  of  NaHO. — Absolute  carbolic  acid  is  completely  soluble  in  an 
equal  volume  of  soda  solution  containing  6  per  cent,  of  pure  NaHO 
(free  from  alumina).  Addition  of  more  of  the  alkaline  solution  up  to 
6  volumes  causes  no  change,  the  liquid  remaining  clear.  Absolute 
cresylic  acid  is  insoluble  in  small  proportions  of  6  per  cent,  soda  solu- 
tion. When  a  large  excess  (9  volumes)  is  added,  it  disappears  and 
forms  distinct  crystals. 
Creasote  is  practically  insoluble  in  6  per  cent,  solution  of  soda. 
4.  Solubility  at  I5'5°C.  in  solution  of  Caustic  Soda  containing  91  per 
cent.  a/*  NaHO. —  Absolute  carbolic  acid  is  soluble  in  an  equal  measure 
of  9  per  cent.  soda.     On  addition  of  any  proportion  of  water  up  to  7 
1  These  solutions  contained  respectively  94  and  91  grams  of  water  to  each  6  and 
9  grams  of  pure  caustic  soda. 
