526 
ON  DROPS. 
drops.  For  a  growth-time,  0-333,  we  get  a  drop  weighing 
0-09264  grammes,  while  for  a  growth-time  of  1J  seconds,  we 
get  a  drop  of  only  two-thirds  the  weight.  A  pharmacist  who 
dispenses  100  drops  of  a  liquid  at  the  rate  of  three  drops  a 
second,  will  give  half  as  much  again  as  another  who  measures 
the  same  liquid  at  the  rate  of  a  drop  every  second  and  a  half. 
One  peculiar  fact  that  appeared  during  these  investigations, 
was  that  when  the  drops  changed  to  a  stream,  from  the  supply 
of  liquid  being  increased,  the  amount  of  oil  having  decreased 
in  quantity,  or  in  other  words,  a  fine  stream  delivered  less  in  a 
given  time,  than  a  series  of  large  drops. 
It  also  appears  that  there  is  no  such  thing  as  a  normal  drop, 
for  at  no  degree  of  slowness  in  dropping  do  the  drops  assume  a 
size  unaffected  by  a  slight  change  in  the  rate  of  their  sequence. 
Professor  Guthrie  has  also  tried  the  effects  of  gradually  de- 
creasing the  strength  of  saline  solutions  dropping  at  the  rate  of 
two  seconds,  and  found  that  decrease  in  solid  constituent  pro- 
duced precisely  the  same  effect  upon  the  size  of  the  drop  as  de- 
crease in  the  growth-rate  in  the  drops  of  a  homogeneous  liquid, 
the  same  apparently  abnormal  maxima  and  minima  presenting 
themselves. " 
In  a  theoretical  point  of  view,  these  peculiar  relations  have 
the  greatest  importance,  and  will  materially  assist  in  determin- 
ing the  relation  between  a  dissolved  solid  and  its  solvent.  The 
secondary  maxima  and  minima  in  the  case  of  the  chloride  of 
calcium  solution,  may  result  from  the  formation  of  definite  hy- 
drates. Professor  Guthrie  does  not  give  the  exact  amount  of 
solid  matter  in  the  chloride  of  calcium  solutions  used,  but  only 
uses  a  nearly  saturated  solution,  and  dilutes  it  with  twice  4,  8, 
16,  32,  &c,  times  its  bulk  of  water.  Had  he  given  us  equiva- 
lent solutions  it  would  have  been  most  interesting. 
These  experiments  remind  us  in  principle  of  those  of  Mr. 
Graham,  in  transpiration  of  fluids,  or  the  passage  of  fluids 
through  capillary  tubes.  Here  similar  apparent  discrepancies 
occurred,  but  they  were  cleared  up  by  the  discovery  that  the 
definite  hydrates  always  exerted  a  peculiar  influence  in  retard- 
ing or  accelerating  the  flow.  In  both  cases  friction  of  a  fluid 
against  a  solid  takes  place,  which  friction  is  diminished  or  in- 
creased primarily,  according  to  the  amount  of  solid  matter  in 
