REMARKS  ON  DIALYSIS. 
315 
poured  into  the  latter,  when  the  process  proceeds  without  fur. 
ther  attention.  In  thus  taking  advantage  of  the  principle  of 
circulatory  displacement,  by  putting  the  liquid  to  be  diffused  at 
the  top  instead  of  at  the  bottom  of  the  water,  the  process  is 
much  facilitated,  especially  where  the  diffusible  body  is  abun- 
dant. 
Thus  arranged,  the  apparatus  is  left  for  hours  or  days,  ac- 
cording to  circumstances,  such  as  the  rapidity  of  the  process, 
or  the  tendency  to  decomposition  by  reason  of  the  warmth  of 
the  weather  or  the  dilution  of  the  diffusate. 
Prof.  Redwood  says:  "  It  may  be  well  to  observe  that  parch- 
ment paper,  or  indeed  any  of  the  substances  named  above,  can 
only  be  used  as  a  septum  in  dialysing  aqueous  liquids.  The 
septum  is  considered  by  Mr.  Graham  to  owe  its  action  to  its 
condition,  in  the  wetted  state,  as  the  hydrate  of  a  colloidal  sub- 
stance, in  which  the  water  of  hydration  is  held  by  a  weak 
affinity,  which  the  superior  affinity  exerted  by  a  crystalloid  can 
overcome.  Hence  there  is  dehydration  taking  place  in  one 
direction,  and  rehydration  in  the  other  direction,  through  the 
septum  during  its  action.  A  septum  suitable  for  dialysing 
alcoholic  and  ethereal  solutions  remains  to  be  discovered. 
Some  form  of  collodion  may  possibly  answer  the  purpose." 
The  following  results  of  dialysis  by  Mr.  Graham  are  given  in 
Prof.  Redwood's  lecture,  viz  : 
Dialysis. 
Twenty-four  hours  at  54°  F. 
Two  per  cent.  Solutions. 
Chloride  of  Sodium, 
Picric  Acid, 
Ammonia, 
Theio, 
Salicin, 
Cane  Sugar, 
Amygdalin, 
Extract  of  Quercitron, 
Extract  of  Logwood, 
Catechu, 
Extract  of  Cochineal, 
Gallo-Tannic  Acid, 
Extract  of  Litmus, 
Purified  Caromel, 
Prof.  Redwood  recommends  a  large-sized  bladder  glass,  as 
Dialysis. 
Relative. 
Twenty -four  hours  at  50°  to  60°  F. 
Relative. 
Diffusate. 
Ten  per  cent.  Solutions. 
Diffusate. 
1000 
Gum  Arabic, 
•004 
1-020 
Starch  Sugar, 
Cane  Sugar, 
•266 
•847 
•214 
•703 
Milk  Sugar, 
•185 
•503 
Mannite, 
•349 
•472 
Glycerin, 
•460 
•311 
Alcohol, 
•676 
.184 
Chloride  of  Sodium, 
1010 
•168 
•159 
•051 
•130 
•019 
•005 
