78 EFFECT OF PHOSPHATES 



It was realised, however, that the experiment was complicated by 

 the fact that the growing crops would probably remove nitrate as 

 rapidly as it was formed, and that the much heavier crops on the 

 slag plots would make a bigger demand on the nitrate supplies than 

 would the crop on the untreated plots. 



To overcome this difficulty a supply of soil, taken to a depth of 

 9 inches, from the slag and untreated plots at Martin's Hearne and 

 Horndon-on-the-Hill was removed, transferred to Chelmsford, broken 

 up, all the green growth removed, and then firmly packed into 10-inch 

 glazed pots provided with a suitable drainage outlet. Particular care 

 was taken to consolidate the soil in the pots by placing weights on 

 the surface for some time and ultimately by tramping. The pots were 

 placed in an open space under atmospheric conditions, and the nitrate 

 nitrogen in the soil determined every fortnight. Samples for analysis 

 were removed both from the field and from the pots by means of a 

 small soil sampler similar to a cheese sampler. 



Estimation of the Nitrate Nitrogen. As soon as possible after 

 the samples were taken generally 4-5 hours in the case of the field 

 soils and 30 minutes in the case of the pots they were dried at a 

 temperature of about 50 C. When dried the samples were finely 

 ground and bottled. The nitrate nitrogen was estimated in the dry 

 ground sample within four days of the sample being removed from 

 the field. 



Method. From 50-100 gns. of soil were placed on a Biichner funnel 

 and washed with several portions of distilled water until about 400- 

 500 c.c. of filtrate were collected. The filtrate was transferred to a 

 conical flask and then rapidly concentrated to a very small bulk 

 about 50-60 c.c. with 10 c.c. of normal caustic soda. The concentrated 

 liquid so obtained was diluted with distilled water and boiled again 

 for 10 minutes. The flask was cooled and 1 gram of finely powdered 

 Devarda's alloy added. The contents were distilled into 10 c.c. of 

 N/50 sulphuric acid, a specially prepared trap being used to prevent 

 spitting. The burner was adjusted so that distillation proceeded 

 slowly for about 5-10 minutes, at the end of which period distilla- 

 tion was quickened so that about half the liquid passed over in 

 30 minutes. Methyl red (-05 % solution in alcohol) was used as an 

 indicator. 



The accumulation of Nitrate in the Pots. The soils representing 

 Plots 2 and 3 at Martin's Hearne were potted on March 29th, and 

 16 days later the first nitrate determinations were made. The soils 

 from Plot 16 (untreated) and Plot 17 (basic slag) at Horndon were 



