5^4 
Varieties. 
Am.  Jour.  Pharm„ 
Dec  ,  1876. 
of  the  liquid  through  the  engorgement  of  the  channels  ;  hence,  per- 
haps, by  absorption,  leading  to  the  softening  and  liquefaction  of  the 
fibrous  and  vascular  element  of  the  sap  wood. 
In  this  phenomenon  the  easterly  winds  have  a  share,  their  high  tem- 
perature and  dryness  favoring  the  determination  of  the  sap  to  the 
exterior.  Their  influence  is  not,  as  often  stated,  limited  to  the  pro- 
duction of  cracks  in  the  bark.  It  will  be  seen  that  there  is  a  great 
analogy  between  the  mode  of  the  formation  of  a  verek  gum  and  that 
of  the  gum  of  Rosaceae,  as  described  by  Tr£cul. 
Recently  an  important  part  in  the  production  of  the  Senegal  gums, 
has  been  attributed  to  a  loranthaceous  parasite,  which  is  met  with  fre- 
quently in  Eastern  Africa,  not  only  on  gum  trees,  but  also  on  guava 
trees,  palms,  etc.  The  author  has  never  observed  the  least  exuda- 
tion of  gum  at  the  points  of  implantation  of  this  parasite,  which  itself 
takes  up  sap,  and  leaves  no  excess  for  the  plant  on  which  it  is  devel- 
oped. The  nodosities,  which  have  probably  been  attributed  to  the 
action  of  this  parasite  and  thus  led  to  the  suggestion,  the  author  con- 
siders to  be  the  results  of  insect  punctures. — Pharm.  Journ.  and  Trans. > 
Oct.  21,  1876. 
VARIETIES. 
Etching  on  glass. — By  E.  Siegwart. — Since  hydrofluoric  acid  can  be  sold 
cheaply,  it  seems  to  be  more  and  more  used  for  the  decoration  of  glass.  This  can 
be  easily  understood,  as  glass  articles,  when  sufficiently  etched,  will  have  a  much 
better  appearance  than  engravings  on  glass.  The  best  decorations  are  obtained  by 
etching  several  portions  of  the  glass  surface  with  ammonium  fluoride  slightly  acidi- 
fied with  acetic  acid.  If  plates  of  glass  are  to  have  an  ice-like  lustre,  the  glass  is, 
in  the  first  place,  covered  with  a  layer  of  very  small  shot,  over  which  very  dilute 
hydrofluoric  acid  is  then  poured.  Results  similar  to  etched  photographs  are  ob- 
tained by  exposing  any  negative  picture  on  a  layer  of  gum  or  caoutchouc-layer 
rendered  sensitive  by  potassium  bichromate,  and  then  dusting  it  with  red  lead.  The 
red  negative  thus  obtained  is  fixed  as  usual,  and  burnt  in,  and  the  more  soluble  lead 
glass  thus  obtained  is  treated  with  concentrated  nitric  acid,  whereby  a  dull  white 
picture  is  produced,  appearing  positive  when  looked  through. — Jour.  Chem.  Society 
[Lond.],  from  Dingl.  polyt.  J.,  ccxx,  479-480. 
On  the  Preparation  of  Some  Colored  Fires  (Bengal  Lights)  Used  in 
Pyrotechny. — By  Sergius  Kern,  St.  Petersburg. — In  preparing  colored  fires  for  fire- 
works by  means  of  the  usual  formulae  given  in  many  manuals  of  pyrotechny  it  is 
often  very  necessary  to  know  the  quickness  of  burning  of  colored  fires,  so  as  in 
