CHEMICAL CHANGES 213 



was also added. Silica medium was prepared by treating water 

 glass (sodium silicate) with hydrochloric acid, and dialyzing in 

 distilled water until free from salts. The solution of silica was 

 then concentrated, nutrient salts added (in proportions referred 

 to above), and the liquid seeded with one drop of the culture 

 mentioned above. The mixture was poured into a sterilized 

 petri dish, and a drop of a saturated solution of salt added to 

 coagulate the silica. This mineral jelly was very unfavorable to 

 the growth of any except the nitro-organisms. 



The bacteria grow as very small colonies, but on the surface 

 they form a white crust. Stained with dye, and examined under 

 the microscope, they appear as round or roundish organisms. 

 Winogradsky separated three varieties of nitrous bacteria : Nitro- 

 somonas europaea from Europe, Nitrosomonas javanesis from 

 Java, and Nitrosococcus from America. 



Study of Nitrification. Nitrification may be studied in culture 

 solutions, or in the soil, and each method has its advantages for 

 certain kinds of work. 



A culture solution may be prepared as follows i 1 



Distilled water 1,000 cc. 



Ammonium sulphate 2.0 gram 



Potassium phosphate I .o " 



Magnesium sulphate 0.5 " 



Ferric sulphate 0.4 " 



Sodium chloride 2.0 4< 



To each 100 cc. portion, i.o gm. magnesium carbonate is added. 

 The solution is inoculated with a small amount of soil, or with 

 soil extract, and incubated for 25 to 50 days. The quantity of 

 nitrous and nitric nitrogen is then estimated. This method may 

 be used for studying the effect of temperature, light, etc., or for 

 estimating the inoculating power of soils held under different 

 conditions. The differences in the effect of soils inoculated into 

 different solutions will, of course, be due to differences in the 

 number and activity of the organisms in them. 

 1 Lipman, Report New Jersey Exp. Sia., 1907, p. 176. 



