326 
Mr.  S.  A.  Shorter  on  the 
Experiments  carried  out  in  this  apparatus  showed  that  the 
continuous  evaporation  promoted  by  the  calcium  chloride  had 
a  marked  effect.  The  fluctuations  in  the  density  were  totally 
eliminated,  the  elasticity  steadily  increasing  to  a  maximum 
much  greater  than  any  value  attained  when  the  solution  was 
exposed  to  the  air  of  the  room. 
In  the  following  table  are  summarized  the  results  of  a 
number  of  experiments  carried  out  with  solutions  of  different 
strengths. 
Table  II, 
Age  of 
Concentration  :  1  part  in 
Surface 
(days). 
100. 
500. 
10,000. 
100,000. 
200.000. 
106. 
107. 
108. 
1  
2  
3  
4  
5  
6  
7  
8  
12  
14  
17  
21  
24  
30  
332 
393 
408 
467 
468 
474 
478 
523 
543 
574 
595 
597 
593 
371 
427 
535 
581 
612 
626 
629 
648 
648 
644 
390 
490 
556 
630 
628 
626 
464 
531 
533 
364 
427 
460 
464 
465 
471 
W6 
81 
100 
186 
200 
0 
0 
The  most  striking  fact  illustrated  by  the  above  table  is 
that  increase  of  concentration  beyond  a  certain  point  is 
unfavourable  to  the  process  of  surface  separation,  causing  a 
slight  decrease  in  the  maximum  value  of  the  surface-rigidity 
and  a  very  great  decrease  in  the  speed  with  which  the 
maximum  is  attained.  There  is  a  marked  difference  in  this 
respect  between  a  1  per  cent,  and  a  '0005  per  cent,  solution. 
The  latter  attains  a  well-defined  maximum  in  three  days, 
while  in  the  case  of  the  strong  solution  the  increase  proceeds 
very  sluggishly  and  irregularly  for  a  period  of  about  three 
weeks  before  a  maximum  is  reached. 
The  action  of  continuous  evaporation  in  causing  a  higher 
degree  of  elasticity  to  be  attained  may  be  partially  explained 
in  the  following  way.  When  the  solution  is  exposed  to  the 
air  of  a  room  whose  temperature  fluctuates,  there  will  be 
certain  periods  during  which  water  is  evaporating  from  the 
surface  and  other  periods  when  water- vapour  is  being  con- 
densed on  the  surface.  When  the  elasticity  has  reached  a 
stage  when  the  increase  is  very  slow,  continued  evaporation 
