356 Journal of Agricultural Research voi. x. N0.7 



the Standard Oil Co., was found to be admirably suited physically for this 

 purpose. The method of study consisted in transferring to glass jars 

 solid undisturbed cores of soil 5 inches in diameter and of varying length 

 and in preventing aeration except through the normal surface. Subse- 

 quent measurements of the nitrate-nitrogen content at varying depths 

 were made. To prevent aeration on the sides and bottom, melted Paro- 

 wax was poured around the column of soil until it filled the space be- 

 tween the soil and jar, thus very effectually preventing the access of 

 oxygen except from surface. A large number of experiments of this 

 nature, in which aeration was varied by drawing a current of air through 

 the column and by varying the physical condition of the column of soil, 

 were carefully planned and executed. 



In all instances where the Parowax came in intimate contact with 

 the soil the accumulation of nitrate nitrogen, in spite of the fact that the 

 other conditions favored nitrification, was so irregular and so unexpected 

 that the results were absolutely inexplicable. The only outstanding fact 

 to be gathered from the mass of data accumulated from the experiments 

 was the apparent inhibitory effect the Parowax exerted upon the ac- 

 cumulation of nitrate nitrogen. 



It was thought possible that the Parowax contained something toxic 

 to the nitrifying organisms, but the substitution of paraffin prepared by 

 Sargent & Co. for scientific purposes (M. P. 50°) did not alter the results. 

 Studies were therefore initiated to ascertain, quaUtatively and quanti- 

 tatively, just what effect such substances produced upon biological 

 activity in general and particularly upon the accumulation of nitrate 

 nitrogen in the soil. In Tables I, II, and III are given data secured from 

 typical experifments. 



In all these experiments a soil possessing a vigorous ammonia and 

 nitrate-forming flora was used in loo-gm. samples. From the results of 

 the controls, in which no paraffin was used, the activity of the flora is 

 shown to be very vigorous. The containers in all experiments were 

 500-C. c. wide-mouthed cotton-plugged bottles. Calcium carbonate was 

 added to some samples and not to others. Samples were incubated with 

 no addition of nitrogen, with nitrogen in the form of ammonium sulphate, 

 and with nitrogen in the form of cottonseed meal. Incubation was in all 

 cases at room temperature, and the moisture loss was replaced at frequent 

 intervals. Where bottles are spoken of as being "Parowaxed" or 

 "paraffined" the hot, melted substance was poured into the bottle, which 

 was tilted so that the liquid would come in contact with all the inner sur- 

 face, and the excess poured off. Where paraffin and Parowax were added 

 direct to the soil, they were in the form of thin shavings made by scraping a 

 cold bar of the solid substance. Paraffin oil was added by measuring from a 

 pipette the desired quantity. After all additions were made and thoroughly 

 mixed in, the moisture content of the soil was adjusted to optimum. 



Nitrate nitrogen was determined colorimetrically and is reported as 

 milligrams of NO3 per 100 gm. of soil. Ammonia nitrogen was de- 

 termined by the magnesium-oxid distillation method and reported as 



