G. W. Robinson 289 



ceases. In the case of soils with large j^roportions of organic matter, more 

 peroxide will be needed. The beaker is then removed from the water bath 

 and, after adding about 100 c.c. of water, boiled for about 15 minutes. 

 A considerable oxidation of organic matter has now taken place and 

 the oxidised material acquires the yellowish or light brown colour of a 

 non-humous subsoil. The contents of the beaker remain approximately 

 neutral so that no solution of mineral matter may be apprehended. In 

 order to form some idea of the effect of this oxidation on the soil organic 

 matter two soils were oxidised. After filtration and washing the residual 

 material was dried and the loss on ignition determined. The filtrate and 

 washings were evaporated to dryness and the amount of soluble organic 

 matter determined. A separate experiment was also carried out in which 

 the gaseous products were collected in normal sodium hydroxide and the 

 amount of carbon dioxide estimated by double titration. The amount 

 of organic matter completely oxidised to carbon dioxide was found by 

 multiplying the weight of carbon found as carbon dioxide by 2, assuming 

 as a first approximation that the organic matter contained 50 per cent. 

 of carbon. The results obtained were as follows: 



Loss on ignition t).\idised Soluble 



Soil Loss on ignition after oxidation to T'O., org. matter 



Cili 2.5-4 8-1 o-,5 10-8 



4T 101 40 1-9 3 7 



It \vill be seen that the original organic matter is approximately 

 accounted for by the unoxidised matter and the products of oxidation. 



A number of soils thus oxidised were submitted to mechanical 

 analysis. The result of the treatment is to break down the compound 

 particles very thoroughly and the separation of the fine gravel and 

 coarse sand by means of the 100 mesh sieve is very easily effected with 

 very little trituration. Generally speaking the sedimentations were 

 carried out twice without the addition of ammonia and then as in the 

 ordinary method. It may be added that the soluble products of oxidation 

 would appear to be deflocculating in their action and quite considerable 

 quantities of clay can be obtained without the use of ammonia. The 

 following table shows the results obtained for a number of soils by the 

 ordinary method including the usual preliminary treatment with HCl, 

 and also by the hydrogen peroxide method, in which this acid treatment 

 is omitted. 



20- 



