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tube containing copper and nitric acid, because the nitrous acid 
cannot accumulate round the copper. 
Summary and Conclusion: 
1. The velocity of solution of anhydrous ferric sulphate can be 
increased by the presence of sulphurous acid, stannous chloride, 
ferrous sulphate ete. No satisfactory explanation of reactions of this 
type is forthcoming. 
2. The action of nitric acid (20°/,) on copper has been studied 
in the presence of various substances and it has been observed that 
when the nitric acid is in excess and the whole of the copper is 
made to dissolve, ferrous and ferric salts exert a marked accele- 
rating effect. In the light of the present investigation, the view 
hitherto aecepted as regards the part played by ferrous salts in des- 
troying nitrous acid, has to be modified. As a matter of fact, it has 
been proved that nitrous acid, which is the active substance in this 
reaction, is formed by the action of nitrie acid on ferrous salts. 
Oxidizing agents like H,O,, KMnO,, H,Cr,O, ete. destroy the nitrous 
acid and hence retard the change. 
Out of the 56 substances, the effect of which was investigated, 
22 act as accelerators and 22 exert a retarding influence in all 
concentrations; whilst 8 of them are slight accelerators in small 
concentrations and are retarders in concentrated solutions. Four of 
these 56 substances have been found to be neutral in small and 
retarders in large concentrations. 
My best thanks are due to the van ’r Horr Fund Committee for 
a grant for this research. 
Chemical Laboratory, Muir Central College, Allahabad, India. 
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