E. J. Russell and E. H. Richards 



539 



more perfect aerobic conditions than is otherwise possible: by letting 

 in the oxygen in quantities of 80 to 100 c.c. at a time — corresponding 

 to a difference of pressure of 50 to 60 mm. — it can be driven into every 

 part of the manure with much more certainty than when a slow air 

 current is passed through and diffusion is the only factor at work. 



In the second experiment this more complete aeration was attained 

 and the result was entirely different. Decomposition was rapid, and 

 no less than 17-2 grams of dry matter disappeared; quantities of CO2 

 were evolved ; but there was no loss of nitrogen. 



The changes in the manure (bullock manure)^ were: 



At start 

 After 20 days 



Percentage composition 



^ -^ Weight of 



Total Nitrogen manure 

 Nitrogen as NH3 grams 



0-504 0-076 502-0 

 0-525 0-083 500-0 



Weight in grams of 



Dry 

 matter 



24-80 

 21-45 



Loss, grams 2-0 



Dry 



matter 



124-5 

 107-3 



17.2 



Total 

 Nitrogen 



2-53 

 2-63 



nil 



Nitrogen 

 as NHj 



0-38 

 0-41 



nil 



Nor was there any gain in the nitrogen gas. 

 The changes in the air of the apparatus were : 



Percentage composition Volume in c.c. reduced to n.t.p. 



Thus the change has been only 20 c.c, too small to be regarded as 

 significant^. In this experiment, therefore, the analyses both of the 

 manure and of the gas agree in showing that mo evolution of nitrogen 

 occurred. 



^ The manure was fresher and contained more straw than the last sample ; its content 

 of nitrogen was lower. 



* At first sight 20 c.c. may appear to be rather a large experimental error. It is 

 however exceedingly difficult to get an accurate value for the initial and final volumes 

 of air. The apparatus is in effect a volumenometer, and in addition to the difficulties 

 inherent in this form, there is the further difficulty that the tension of aqueous vapour 

 is not constant throughout, but is different in the flask from what it is in the reagent 

 bulbs B or C, or the capacity bulb on the way back from the pump to the flask. These 

 uncertainties cause errors in the initial and final amounts, and therefore still greater 

 errors in the difference used in these calculations. The difference observed in the 

 experiment on p. 538 is six times the error of the experiment. 



