RELATION OF ALGAE TO DISSOLVED GASES. 193 
upon of driving these gases, as generated, through a series of 
flasks partly filled with tap water or pond water, and contain- 
ing the alg most available or most likely to respond. 
Accordingly, small Erlenmeyer flasks were fitted with two- 
holed stoppers. Into one hole was a leading-in tube of glass 
reaching to the bottom. From the other hole was a leading- 
out tube of glass going to another flask like the first, and 
reaching nearly to the bottom of the same; and so on through 
the series. In the same manner the gas driven in at one end 
could, with little pressure, be forced through the entire series 
and leave them all saturated and filled with the gas. 
Into each flask was put 50 ce. of tap water and a small 
amount of selected alga. Each flask contained only one 
species, although there was no attempt at pure cultures nor 
to rigidly exclude all others. : 
The generator was connected and the gas passed in to as 
near saturation as possible; then it was left in diffuse light at 
ordinary room temperatures, 18° to 20° C. They were left so 
for about a week when they were again charged with gas. 
There were two series; one to be treated with oxygen and the 
other with carbon-dioxide. A third series for control was not 
to be treated with either. 
In order to secure purity of gases and prevent any poison- 
ous or ill effect from that source, a wash-bottle was placed in 
series between the generator and the culture flasks. The 
wash-bottle for the COz generator contained a solution of 
sodium bicarbonate to arrest any HCl gas that might escape 
from the generator, in which hydrochloric acid and lumps 
of marble were used. The gas was tested until it gave no 
precipitate with AgNOs. Preliminary trials showed that this 
was necessary, as some HCl came over when the wash-bottle 
was not used, as shown by the above test and the blackening 
of the plants in the first flasks. 
For the oxygen generator the wash-bottle contained only 
water, as there was no volatile substance nor anything in- 
jurious except a little NaOH and a compound of copper in the 
“oxone,” a sodium peroxide compound used for the genera- 
tion of the oxygen. 
