CHEMICAL CHANGES 



211 



Distilled water 1,000 cc. 



Potassium phosphate i gram 



Magnesium sulphate 0.5 " 



Calcium chloride trace 



Potassium nitrite 0.2 gram 



After sterilization, 100 cc. of the solution is inoculated with 

 about o.i gm. moist soil. This medium is unfavorable to all 

 bacteria except the nitrate organism. After the nitrate organism 



Fig. 49.- Microscopic appearance of nitrous bacteria. Winogradski. 



has developed, as shown by the formation of nitrates and the 

 weakening or disappearance of the nitrous acid, a few drops of 

 the culture are diluted with sterilized water, and fresh portions of 

 the medium seeded with single drops of the diluted culture. Some 

 of these cultures will probably contain only the nitrate organism, 

 but at any rate, the other bacteria can be eliminated by a few 

 more cultures. The purity is tested by plating with a 

 drop from each culture. The nitrate organism does not 



