1. Six per cent. peroxide is found to be unsuitable as a reagent for the determination of the “degree of humification” of soil organic matter, as it oxidises not only compounds containing carbon and nitrogen but also a varying amount of a substance containing carbon but no nitrogen, this amount depending on the volume of reagent used and the total amount of carbon originally present in the quantity of soil employed.

2. There are apparently two phases in the attack of peroxide on soil organic matter. In the first phase, material containing carbon and nitrogen is oxidised, whilst in the second phase the material oxidised consists solely of nitrogen-free carbon compounds.

3. By the use of 3 per cent. peroxide (2 per cent, or less may be preferable for some soils) the attack on soil organic matter can be restricted to the first phase. The material thus oxidised appears to be built up by the association of a protein complex with a carbohydrate complex of high carbon content. Its carbon-nitrogen ratio is about 10:1.