AprnEy—On Absorption of Oxygen by Polluted Waters, &c. 285 
temperatures from 15° to 18° C. in 48 hours. For tidal waters of 
the most favourable character for the disposal of sewage, the 
allowable absorption may amount to 3°5 e.c. per litre in 64 hours, 
or 4:0 ce. per litre in 125 hours. 
An apparatus capable of indicating volumes of these dimen- 
sions, and at the same time of permitting the use of volumes of 
polluted water sufficiently large for subsequent chemical analysis, 
if such be necessary, should be as follows :—A and B should 
each have a capacity of 1200 ec., which permits the use of 
1000 cc. of polluted water, and provides for an air-space of 
200 cc. The capillary portion of aa should be as short as possible 
in all forms of the apparatus. The bottle should consequently 
be made as shallow as possible; and for this purpose it is 
advantageous to have the necks of the bottles depressed as shown 
in the diagram, but this is not essential. The graduated portion 
should have a capacity of 3 c.c.; and its fine divisions should give 
readings in 1/20th ec. The tube would then be about 112 mm. 
long, and 5°5 mm. bore. The volume of the bulb a, should be 
about 1 c.e. 
The total loss of oxygen in the atmosphere of B observable 
by means of an apparatus of these dimensions would slightly 
exceed 10 c.c. per litre of water before replenishing the oxygen 
absorbed in 2 by fresh oxygen in the manner to be described 
later on. 
The dimensions of an apparatus required for the second 
purpose would be such that Ad and B would each have a capacity 
of 1500 e.c., and would allow of the employment of 1000 c.c. of 
the polluted water, and the provision of an air-space of 500 c.e. 
The graduated tube should measure a total volume of 5 c.c:, and 
afford readings in 1/20thc.c. A tube of this capacity would be 
about 186 mm. long, and 55 mm. bore. The capacity of the 
bulb a, should be 5 c.c. 
For the third of the above-enumerated purposes, 4 and B 
should each have a capacity of 1500 cc. The graduated tube 
should give readings in 1/10th e.c., with a total of 10 ce. Such 
a tube would be about 225 mm. long and 7 mm. bore. The 
bulb a should have a capacity of 10 cc. 
The maximum volume of oxygen absorbed in B, which would 
be recordable by this last apparatus, would slightly exceed 50 c.c. 
