CHEMOSYNTHESIS OF CARBOHYDRATES 



237 



5 minutes, the potassium solution absorbing the carbon dioxide. 

 Lower the open burette c and draw the air off into the cali- 

 brated burette and read its volume. The difference between 

 this and the previous reading will denote the amount of carbon di- 

 oxide originally present (See Fig. 1 19). 



Fill the cylindrical bulb of a second 

 absorption pipette with sticks of pho- 

 sphorus about 3 mm. in diameter and 

 fill with distilled water. Draw the air 

 in the graduated burette into this 

 pipette and allow it to remain for a few 

 minutes and the oxygen will be taken 

 up by the phosphorus. Force back 

 into the burette and measure as before. 



It is important that all connections 

 should be made with tubing of a 

 capillary bore and care must be taken 

 throughout that no air except that 

 taken from thc~ bell-jar is included 

 in the portions tested (See also 327). 



303. Photosynthesis by Bacteria. A 

 number of bacterial forms are found 

 to give off oxygen when illuminated. Fia. 119. Hempel's gas burettes. 

 Certain of these including Ckromatium & ^ che& to P ! P ette containin g 



. .11 ., 1 potassium hydrate, showing meth- 



Okem are furnished with chlorophyl od of fordng air into the latt£r 



and carry on photosynthesis. Others, 



however, furnished with some compound of lipochrome, hold 



oxygen in loose combination and give it off when exposed to 



light. 1 



304. Chemosynthesis of Carbohydrates. The synthesis of carbo- 

 hydrates by means of energy derived from chemical compounds 

 has been demonstrated in the nitrate and nitrite bacteria only. 

 The nitrite bacteria absorb and oxidize ammonia to nitrous acid, and 



1 Ewart, A. J. On the evolution of oxygen from colored bacteria. Jour. Linn. 

 Soc. 33 : 123. 1897. 



