84       PRODUCTION  OF  CRYSTALLINE  LIMESTONE  BY  HEAT. 
the  surface  of  the  acid.  The  zone  turns  yellow  on  its  lower 
surface,  but  remains  without  further  change  for  some  hours. 
By  carefully  shaking,  the  glass  the  rose  color  may  be  made  to 
reappear  above  the  yellow  zone. 
A  cubic  centimetre  of  water  containing  to  <jo  otn  of  nitric  acid 
shows  the  reaction  very  decidedly,  but  it  may  be  seen  when  the 
amount  of  acid  is  ten  times  less. 
As  the  sulphuric  acid,  the  brucine,  and  water  employed  to 
dissolve  it  may  contain  nitric  acid,  this  source  of  fallacy  must 
Be  guarded  against,  and  the  author  recommends  that  the  water 
should  be  distilled  from  potash,  the  sulphuric  acid  distilled  with 
about  5  per  cent,  of  carbonate  of  ammonia  collecting  only  three- 
fourths  of  the  acid,  and  the  brucine  well  washed  with  distilled 
water. — Chem.  News,  London,  Oct,  17,  1863. 
ON  THE  PRODUCTION    OF   CRYSTALLINE  LIMESTONE 
.     BY  HEAT. 
In  this  Journal,  vol  xxxii.  p.  112,  an  abstract  is  given  of 
Rose's  experiments  on  the  deportment  of  carbonate  of  lime  at  a 
high  temperature.  Among  other  interesting  conclusions  drawn 
by  Rose,  he  says  that  "  chalk  or  compact  limestone  cannot  be 
converted  into  crystalline  limestone  (or  calc-spar)  by  exposure 
to  a  high  temperature  in  closed  vessels,  and  as  a  general  fact, 
that  rhombohedral  carbonate  of  lime  is  not  formed  in  the  dry 
way."  Further,  "  that  the  so-called  crystalline  marble,  ob- 
tained by  Sir  James  Hall  in  his  experiments,  was  probably  noth- 
ing more  than  a  slightly  coherent  but  otherwise  unaltered  mass, 
which  Hall  erroneously  considered  to  be  crystalline  marble." 
Rose  states,  in  a  recent  communication  to  the  Berlin  Academy 
of  Sciences,  that  he  was  not  entirely  satisfied  with  his  former  re- 
sults, especially  as  Dr.  Horner,  President  of  the  Geological  So- 
ciety of  London,  assured  him  that  he  had  inspected  the  speci- 
men of  marble  made  by  Sir  James  Hall,  and  that  it  differed  en- 
tirely from  the  amorphous  product  obtained  in  the  Berlin  experi- 
ments. Rose,  therefore,  repeated  his  investigations  on  the  sub- 
ject, and  has  now  obtained  results  which  differ  entirely  from 
those  he  formerly  published,  and  which  fully  confirm  the  correct- 
ness of  Sir  James  Hall's  conclusion,  that  marble  can  be  produced 
by  exposing  massive  carbonate  of  lime  to  a  high  temperature  under 
