544 FERGUSON: OXIDATION OF LAVA 



The results obtained in the experiments at atmospheric pres- 

 sure and at a low pressure of nitrogen are given in table i. 



In addition, the results of two miscellaneous experiments are 

 given below. 



( 1 9) Some of the lava powder was heated in a platinum crucible 

 in air over a Meker burner for two hours. The ferrous iron 

 content was then found to be 1.94 per cent. 



(20) Some of the oxidized product obtained in experiment 

 (19) was heated in a partial vacuum (o.i mm. of nitrogen) for 

 4 hours at iioo°C. The ferrous iron value was then found to 

 have been raised from 1.94 to 3.90 per cent. A duplicate analy- 

 sis gave 3.87 per cent. 



Discussion. — The results given in table i show that after 

 heating there is a decrease in the ferrous iron content of the rock 

 amounting, in terms of the ferrous iron originally present, to 

 4-9 per cent for the coarse powder and 11-16 per cent for the 

 fine powder. The variations within each group are not trace- 

 able in any way to the gas phase present. In fact the steam 

 appears to have acted like an inert gas.^^ 



Just what is the complete cause of the decrease noted is some- 

 what of a question. A certain apparent decrease in the ferrous 

 iron content might be expected from the loss of the reducing 

 gases which are liberated upon heating the lava, and some de- 

 crease might also arise from the taking up of some iron by the 

 platinum boat.^^ An actual decrease would occur if part of the 

 ferrous iron were oxidized by adsorbed gases. These effects, 

 would, however, be expected to be small. 



The decrease in ferrous iron must therefore be ascribed mainly 

 to some reaction within the lava sample itself. The magnetite 

 which formed when the lava crystallized^'* was probably the last 



^2 It cannot be argued that the gas reacted only with the surface material and 

 did not penetrate the charge, for experiment (15) shows that samples from the bottom 

 and top of the charge contain exactly the same amoimt of ferrous iron. Also it can 

 hardly be argued that there was a surface attack upon the lava grains since the re- 

 sults with both fine and coarse materials show the same independence of the gas 

 phase, and the same final ferrous iron content. 



'' SosMAN, R. B., and Hostetter, J. C, This Joltrnal. 5: 293. 1915. 



^* After an experiment the material was found completely crystallized, although 

 originally containing much glass. 



