Am.  Tour.  Pharm. 
Sept.  1919. 
Applied  Crystallography. 
615 
APPLIED  CRYSTALLOGRAPHY.1 
By  Hexry  Leffmaxn,  M.D.. 
Philadelphia. 
Crystals  are  attractive  to  the  learned  and  unlearned.  The 
crystalline  form  of  any  given  substance  is  always  more  striking 
than  the  amorphous  form,  gives  better  evidence  of  purity  and  serves 
far  better  for  identification.  Most  chemists,,  however,  are  not 
deeply  learned  in  crystallographic  lore.,  whether  engaged  in  teach- 
ing, research  or  analyses  in  the  commercial  or  works  laboratory. 
The  pharmaceutic  chemist  depends  to  a  limited  extent  on  the  crys- 
talline form  of  the  common  medicinal  salts,  but  it  is  the  mineralogist 
who  has  cultivated  the  science  of  crystallography  to  the  greatest 
extent.  The  crystals  of  natural  minerals  are  usually  50  large  and 
so  characteristic  as  to  constitute  one  of  the  most  important  means 
of  identification,  indeed,  this  feature  has  dominated  mineralogy  to 
such  an  extent  that  it  has  become  largely  a  science  of  external  form, 
rather  than  chemical  constitution.  The  mathematical  exposition  of 
crystals  is  complex  and  abstruse.  Chemists  generally  take  no  in- 
terest in  it.  They  do  not  trouble  themselves  with  the  mysteries 
of  the  basal  pinacoid.  hemihedral  and  tetartohedral  modifications  or 
enantiomorphism.  This  is  largely  due,  of  course,  to  the  fact  that 
the  chemist  deals  in  the  main  with  artificial  substances  of  which  the 
crystals  are  minute  and  imperfect,  and  even  when  dealing  with  a 
crystal  of  an  artificial  substance  produced  on  the  large  scale  and, 
therefore,  presenting  distinct  form,  the  practical  chemist  prefers 
only  to  rely  on  chemical  tests  rather  than  optical  and  geometric 
methods. 
The  microscope  is  much  more  in  evidence  in  the  chemical  labora- 
tory than  it  was  fifty  years  ago,  but  even  now  in  many  of  its  ap- 
plications no  use  is  made  of  the  valuable  accessory  appliances  that 
mineralogists  and  especially  petrologists  employ.  In  clinical,  phys- 
iologic and  toxiologic  chemistry  most  workers  are  still  satisfied  to 
describe  the  crystal  forms  that  they  find  in  the  microscope  field  by 
such  common  terms  as  "  stellate,"  "  needle-shaped,"  "  plate-like." 
We  still  hear  of  the  "  dumbbell "  crystals  of  calcium  oxalate — or 
oxalate  of  lime,  as  clinicians  persist  in  calling  it — and  of  the  "  coffin- 
1  Reprinted  from  The  Catalyst. 
