±4 inches of water was created by a 3° F. tem- 

 perature variation. A safety valve was designed 

 to prevent greater fluctuations (fig. 10). The de- 

 irice was composed of two vessels containing so- 

 dium hydroxide solution to the level that pressure 

 inside the chamber or outside would force air 

 through the safety valve at a rate great enough 

 to prevent dangerous pressure buildup. Air pass- 



ing through the trap was washed free of C0 2 and 

 radioactivity. This prevented radioactive con- 

 tamination from exhaust air and changes in spe- 

 cific activity of C0 2 in the chamber by incoming 

 air. This trap is rarely required to function. 



A manometer is located on the end of the cham- 

 ber to indicate pressure differences between the 

 inside and the outside of the chamber. 



OPERATION OF THE CHAMBER 



Soybeans, corn, wheat, and tobacco have been 

 grown in the biosynthesis chamber. Although the 

 same system of culture and environmental control 

 was used for all crops, each crop presented differ- 

 ent nutritional problems. 



With all the crops except tobacco the seeds were 

 germinated between moist layers of muslin in a 

 Pyrex tray on a stainless steel screen, then trans- 

 ferred to nutrient solution for a few days for root 

 and stem elongation. The soybean plants were 

 then placed in the chamber supported in cork stop- 

 pers with their roots in nutrient solution. The 

 3orn and wheat plants were supported in funnels 



filled with sand. These funnels were made from 

 200-ml. Erlenmeyer flasks from which the bot- 

 toms had been removed. The necks of the funnels 

 extended into the nutrient solution in the culture 

 vessels. 



The basic nutrient used was one described by 

 Steinberg (8) and modified by reducing the phos- 

 phorus concentration to half. The normal con- 

 centration of phosphorus was too high for grow- 

 ing plants in the high C0 2 concentration of the 

 chamber, because the solubility of the solid phase 

 calcium phosphate was increased and the phos- 

 phorus precipitated the iron. For soybeans 10 



\ 



Figure 10.— An end view of the carbon-14 biosynthesis chamber. 



11 



