620 
Sesquiterpenes. 
Am  Jour.  Pharm. 
Dec,  1892. 
rapidly  as  the  concentration  is  increased  to  15  per  cent.;  beyond 
this  point  it  may  be  represented  by  a  line  passing  through  the  zero 
point  when  the  concentration  is  100  per  cent. 
Nitrous  Acid. — At  a  temperature  of  18-210,  the  production 
increases  rapidly  with  the  temperature  until  a  concentration  of  14 
per  cent,  of  nitric  acid  is  attained  ;  it  then  falls  with  equal  rapidity 
with  increase  of  concentration  to  30  per  cent.,  at  which  stage  nitrous 
acid  ceases  to  appear  among  the  final  products. 
Nitric  Peroxide. — Between  1 8°  and  22°,  nitric  peroxide  is  first 
formed  at  a  concentration  of  27  per  cent,  of  acid  ;  it  increases  slowly 
at  first,  rapidly  between  64  per  cent,  and  72  per  cent. ;  beyond  80 
per  cent,  it  remains  almost  constant. 
Nitrous  Oxide. — The 'formation  of  this  compound  takes  place  in 
Comparatively  large  quantities  and  with  great  regularity.  It  reaches 
a  maximum  at  a  concentration  of  40  per  cent,  acid  and  a  minimum 
at  80  per  cent. 
Nitrogen  is  only  formed  in  very  small  quantities  in  acid  of  all 
degrees  of  concentration. 
The  velocity  of  the  dissolution  of  the  zinc  in  nitric  acid  increases 
regularly  with  the  concentration  of  the  acid  below  25  per  cent ;  it 
then  falls  slightly,  remains  constant  between  33  per  cent,  and  42 
per  cent.,  then  diminishes  regularly,  attaining  its  minimum  value  at 
a  concentration  of  68  per  cent.;  a  considerable  rise  then  takes  place 
with  increased  concentration,  but  the  previous  maximum  value  is 
not  again  attained. 
In  conclusion,  the  author  points  out  that  the  hypotheses  that  the 
reduction  of  nitric  acid  is  effected  by  the  direct  action  of  zinc  or  by 
nascent  hydrogen,  both  fail  in  certain  cases,  as  a  larger  quantity  of 
reduction  products  is  formed  than  would  be  theoretically  possible, 
and  suggests  that  the  water  present  enters  into  the  reaction.1 
SESQUITERPENES.2 
While  the  characteristics  of  the  terpenes  are  now  tolerably  well 
known,  so  that  the  recognition  of  the  various  isomers  is  no  longer 
very  difficult,  and  the  knowledge  of  the  mutual  relations,  as  well  as 
1  The  author,  in  referring  to  previous  researches,  makes  no  mention  of  those 
of  Veley  on  the  action  of  nitric  acid  on  metals. — Editors  Jour.  Chem.  Soc. 
2  Abstract  of  a  memoir  by  O.  Wallach  and  W.  Walker,  in  Annalen,  Sept- 
ember 17  ;  reprinted  from  Phar.  Jour,  and  Trans.,  Novbr.  12.  1892. 
