A Soiitli AustralUoi Elaterite. 139 



but containiiis; an opaque, yellowish, frranular precipitate. They 

 •could not be .separated by solubility in carbon bisulphide or 

 ether, but a partial separation was effected by ceutrifuging. 



For comparison, the mean results of the combustions of the 

 soluble and insoluble constituents and the calculated values are 

 again given. It is evident from the table that products I., II. 

 and III. are incompletely oxidized mixtures. 



The Ash. — The ash comprised about 25 per cent, of the sample 

 on which this work was done, but in a latter specimen, since 

 obtained from R. H. Walcott, Esq., F.G.S., of the National 

 Museum, only 5.4 per cent, of ash was found. The analysis 

 failed to show the presence of any phosphates, which would be 

 expected if the Coorongite were of animal origin. The ash had 

 the following composition : — 



Silica ... ... ... ... 95.12 



Aluminium and iron oxides ... ... 3.66 



Calcuim oxide ... .., ... 1.17 



Sodium chloride ... ... ... Trace 



99.95 

 Mr. D. J. Mahony kindly examined the mineral part of 

 Coorongite, and found a number of species of typical fresh- 

 water diatoms. Only a small part consisted of diatoms, the 

 ash being mostly sand, and it is doubtful whether the occurrence 

 of these diatoms is more than accidental. 



Conclusions. — Coorongite has been shown to consist of two 

 substances, one with the formula (CioHigO)^, and the other 

 (CioH.juO;^),^. The physical properties of the substance have 

 earned it the name of Mineral Caoutchouc, and these formulae 

 favour the idea that it is really related to caoutchouc, which has 

 the formula (CjoHi^ja; Caoutchouc oxidizes readily, even taking 



