506  American  Pharmaceutical  Association.  {A ™'J^!imm' 
and  nitric  acids,  ammonia  and  alcohol.  Titration  and  specific  gravity  were  em- 
ployed to  furnish  solutions  of  definite  strengths.  The  indices  of  refraction  for 
sodium  light  of  the  substances  in  the  different  dilutions  are  given  in  tables  for 
comparison  with  the  specific  gravities  and  per  cent,  content. 
In  some  instances  the  increase  in  the  number  that  represents  the  index  of 
refraction  was  quite  regular  for  each  per  cent,  of  increase  of  the  substance  in 
solution  ;  in  others  it  becomes  less  uniform  the  higher  the  percentage  runs. 
Tables  have  been  calculated  from  the  average  increase  and  give  the  per  cent,  of 
content  in  whole  numbers,  compared  with  the  index  of  refraction. 
When  the  differences  in  the  latter,  for  a  difference  of  i  per  cent,  in  content, 
are  too  small  and  variable  to  be  of  practical  use — as  is  experienced  in  the  esti- 
mation of  nitric  acid,  above  60  per  cent.;  acetic  acid,  above  60  per  cent.;  and 
sulphuric  acid,  above  80  per  cent. — it  becomes  necessary  to  take  the  reading  on 
the  refractometer,  as  usual,  then  add  to  the  substance  from  one-fifth  to  one 
volume  of  water,  and  take  the  reading  again  at  the  same  temperature.  The 
dilution  must  be  adjusted  low  enough  to  admit  of  reading  on  the  instrument 
and  reference  to  the  table.  In  the  determination  of  alcohol,  when  the  index 
1*36000  (which  indicates  about  40  per  cent,  content)  is  exceeded,  considerable 
variation  occurs. 
A  paper  on  Hydrocymenes  and  Derivatives,  by  Prof.  Edward  Kremers, 
treated  of  the  constituents  of  volatile  oils,  many  of  which  may  be  considered 
as  derived,  directly  or  indirectly,  from  i  cymene,  C10H14,  a  hydrocarbon  which 
occurs  in  a  number  of  these  oils,  such,  for  instance,  as  those  of  thyme  and 
Cicuta  virosa. 
A  synopsis  of  the  new  nomenclature  as  applied  by  Baeyer  to  the  older  names 
and  of  the  number  of  possible  isomers  may  be  stated  as  follows  : 
Hydrocarbons. — Terpane,  Hexahydrocymene,  C10H20.  Of  this  we  have 
only  one  structure. 
Terpenes,  Tetrahydrocymenes,  Cl0H18.    Six  are  possible. 
The  two,  known  are  carvomenthene  and  menthene. 
Terpadienes,  Dihydrocymenes,  C10H16.  Fourteen  structures  can  be  formed 
for  this  class. 
Pinene  and  camphene  are  placed  in  a  separate  group  by  Baeyer. 
Alcohols. — Terpanols,  Hydroxyhexahydrocymenes,  C10H19OH.  Seven  iso- 
mers are  possible.    Terpan-3-ol  is  ordinary  menthol. 
Terpenols,  Hydroxytetrahydrocymenes,  C10HUOH.  Of  these  there  are 
forty-three  isomers  possible. 
The  terpineols  belong  to  this  group. 
Terpadienols,  Hydroxydihydrocymenes,  C10H15OH. 
Eighty-seven  structures  can  be  produced  to  represent  their  constitutions. 
Terpadiols,  Dihydroxyhexahydrocymenes,  C10H20O2. 
Twenty-four  diatomic  alcohols  of  this  class  are  possible.  Terpin  is  the 
representative. 
Ketones. — Terpanones,  Ketohexahydrocymenes,  C10H18O. 
Of  these  there  are  but  two,  carvomenthone  being  the  a-ketone  and  menthone 
the  /3-ketone. 
Terpenones,  ketotetrahydrocymenes,  C10H16O. 
Eleven  a-ketones  of  this  type  are  possible  and  an  equal  number  of  /3-ketones. 
