Juday—Lakes in Central America . 
231 
and Cayuga lakes had the same temperature, yet the former 
contained one cubic centimeter of oxygen per liter of water less 
than the latter. But if the altitude of the two lakes is taken 
into account, the amount of oxygen in the surface stratum of 
lake Amatitlan was about 4 per cent, above the saturation point 
while in Cayuga lake it was somewhat less than 2 per cent, in 
excess. 
The surface temperatures of Atitlan and Seneca lakes were the 
same but the dissolved oxygen of the former amounted to 2.1 cc. 
less than that of the latter. If corrections be made for the al¬ 
titudes of the two lakes, the quantity of oxygen in the surface 
water of Seneca lake was about 6 per cent, above saturation 
while that in the surface water of lake Atitlan was about 13 per 
cent, below the saturation point. With respect to the volume of 
oxygen found at the various depths it may be said that the ob¬ 
servations were made on the temperate lakes in August when the 
quantity of this gas was near the minimum for the year, while on 
the tropical lakes they were made soon after the close of the win¬ 
ter period of circulation, and at that time their waters should 
contain about the maximum amount for the year. 
Carbon dioxide. The Seyler method 1 was used for the deter¬ 
mination of the carbon dioxide. In this method the degree of 
alkalinity or acidity of the water is obtained by titration with a 
standard solution of an acid or an alkali, as may be necessary, 
using phenolphthalein as an indicator. The fixed carbon diox¬ 
ide is determined by titrating with a standard solution of an 
acid, using methyl orange as an indicator. For these determi¬ 
nations N/44 Na 2 C0 3 and N/44 HC1 were used. 
The greater portion of the carbon dioxide of lake waters is 
generally found in chemical union with other substances, chief 
among which are calcium and magnesium. This combined gas 
exists in two different states. One portion is in a close chemical 
union with these substances and forms their normal carbonates. 
This is known as the fixed or combined carbon dioxide. The 
other part is in a loose union and comprises that portion of this 
gas which converts the normal carbonates into the bicarbonates. 
It is called the half-bound or bicarbonate carbon dioxide. The 
latter is in such a loose chemical union that the chlorophyllous 
organisms are able to use the greater part of it in their photo- 
1 Chem. News, vol. 70, 1894, p. 82, 104, 112, 140 and 151. 
