76 
PRACTICAL  THOUGHTS  ON  LIGHT. 
part  of  the  spectrum  at  the  other  or  violet  end.  It  has  there- 
fore been  assumed  that  the  heating  and  chemical  effects  are  due 
to  vibrations  which,  although  they  accompany  those  of  light, 
are  nevertheless  distinct  from  them.  For  our  present  purpose, 
however,  we  may  consider  that  the  heating,  luminous,  and  che- 
mical effects  of  light  are  associated  with  the  colored  rays  men- 
tioned, and  that  the  heating  and  actinic  rays  are  those  that  do 
the  greatest  amount  of  damage  to  goods.  Yellow  glass  com- 
pletely prevents  actinic  action,  and  white  opaque  glass  is  the 
best  adapted  for  keeping  anything  cool.  It  appears  to  be  quite 
a  mistake  to  keep  wines  and  syrups  in  dark  colored  bottles,  for 
dark  colors  absorb  heat  most  readily;  and  opaque  white  glass 
would  be  cooler,  on  account  of  its  reflecting  the  heat  from  its 
surface  instead  of  absorbing  it.  It  is  quite  evident  that  if  the 
plate-glass  in  our  shop  windows  was  tinted  with  pale  yellow, 
many  things  might  be  placed  in  the  window  without  the  risk  of 
suffering  so  much  damage  as  they  many  times  do ;  and  if  all 
our  bottles  were  tinted  yellow,  many  chemicals  would  keep 
longer  in  good  condition.  It  would  be  interesting  to  know  the 
exact  effects  produced  upon  different  substances  by  keeping 
them  in  bottles  of  various  colors.*  In  some  cases,  such  as  in 
the  preservation  of  salts  of  silver,  the  iodides,  etc.,  yellow  glass 
would  appear  to  be  the  best,  on  account  of  its  preventing  che- 
mical action.  There  might  be  instances  where  chemical  action 
was  not  so  intense  in  its  effects ;  but  where  the  heating  rays  of 
light  do  most  harm  by  elevating  the  temperature  and  giving 
encouragement  to  fermentation,  as  in  the  case  of  syrups,  or  in 
causing  too  much  evaporation,  as  with  ethers,  in  the  first  in- 
stance yellow  glass  bottles  would  be  the  best  antidote,  and  in 
the  second,  white  opaque  glass  would  be  the  best,  because  the 
*  Some  interesting  and  important  information  on  the  effects  produced 
on  vegetable  colors  by  the  different  colored  rays  of  light  will  be  found  in  a 
paper  by  Sir  J.  Herschel,  in  the  Philosophical  Transactions  for  1842.  It 
appears  that  the  vegetable  colors  are  affected  by  the  luminous  rays  rather 
than  the  chemical  ray,  and  that  the  rays  most  effective  in  destroying  a 
particular  color  are  those  which  are  complementary  to  it.  Thus,  vegetable 
blues  are  most  affected  by  the  red  orange  and  yellow  rays,  purple  and 
pinks  by  the  yellow  and  green  rays,  and  orange  yellows  by  the  blue  rays. 
—Ed.  Pharm.  Journ. 
