137 



MANGANIFEROUS NODUl^ES IN THE 

 BOULDER-CLAY OF ESSEX. 



By [MISS] MAY THRESH. 

 \_Read December Uth, 190 J.] 



Some time ago it was remarked that in certain soils in Essex 

 there occurred small nodules which in appearance bore so close a 

 resemblance to seeds that they were almost indistinguishable in 

 situ. It was observed that these nodules were only found in soil 

 overlying the Essex boulder clay. They are brown in colour, 

 often almost a perfect sphere in shape, and very hard. In size 

 they vary considerably, the largest being about five millimeters 

 in diameter and the smallest exceedingly minute. 



A sample of the soil containing these nodules was taken ; 

 they were carefully sorted out and weighed, and it was found 

 that they formed about 'i per cent, of the total weight of soil 

 examined. The nodules were then submitted to a qualitative 

 analysis and were found to contain iron in considerable quanti- 

 ties. It was noticed on the addition of hydrochloric acid that 

 chlorine was given off, proving the unexpected presence of the 

 peroxide of manganese. On separating the insoluble part from 

 the soluble filtrate it was seen that the former consisted of a 

 sandy whitish residue of silica. 



The presence of manganese dioxide rendering the nodules 

 of greater interest, a quantitative analysis was made. The sub- 

 stance was first powdered and a weighed portion was heated to 

 200° C. in order to drive off any water present and determine the 

 percentage of moisture. The dried substance was then digested 

 with strong hydrochloric acid and the metallic compounds were 

 tlms separated from the insoluble silica, which was dried and 

 weighed. The soluble portion containing the chlorides of the 

 metals was next neutralised with ammonium carbonate and the 

 iron was precipitated by means of ammonium acetate, washed, 

 dried, and weighed as ferric oxide. 



The manganese left in the filtrate was precipitated by means 

 of anmionia and a saturated solution of bromine water, dried, 

 and weighed as manganese tetroxide. The calciimi left in the 

 filtrate was precipitated b}' ammonium oxalate, dried and 

 weighed as lime. 



