ELECTko-MO'j i\i'; sicKiKs 01' Till-: M i:t Ai,s. 249 



" nascent " hydrogen. Thi> at oiice reduces the acid, and how 

 far tlie refluction goes, or wliat products ajre formed, depends- 

 (chiefly on the availalilc energy of the nascent hydrogen, i.e., on 

 tile position of the metal in the ]Lloctro-niotive Series. 



With those metals at the top of the series, i.e., K, Na, Ca, and 

 Mg, it is conceivaible that the hydrogen is displaced at such a 

 very g'reat pressure that some of it esoapes oxidation, and so.there 

 may be small quantities of free hydrogen among the gaseous pro- 

 ducts. The chief product of reduction of the HNO3 will, how- 

 e\'er. in such cases be ammonia, i.e., the maximum possi^ble 

 reducliun. With metals somewhat lower in the series nitrogen, 

 N2O and KO will be the chief products, the relative /amrxints of 

 eacli depending upon the conditions oi temperature and concen- 

 tration. 



lint vvJiat about those metals which have no tendency to 

 displace hyrlrogen frotm solution? These metals cannot assume 

 the ionic form directly by displacing hydrogen from its union 

 with lan electric charge. They may, however (if their tenrlency 

 to oxidation is great enough), be oxidised directly iby the nitric 

 acid to oxide, which then dissolves in the acid to form a salt. 

 In this way the tendency of the metal to form ions is satisfied. 

 I'^ven with the metals below hydrogen, however,- there is still a 

 very diflferent tendency towards oxidation corresponding to the 

 position in the series. Copper is oxidiscfl more rearlily than 

 silver, iand silver again more readily than gold. I fence the ]>os- 

 sibility of "parting" gold and silver is really a consequence of 

 rlifiference of position in the Electro-motive Series. As reganls 

 the gaseous products of reduction in the case of metals below 

 liydrogen, the HXOa will not be rerluced as far as is the case 

 with metals higher in the series. Ifence we shoulrl expect chiefly 

 XO and XO2. 



Thus the flilTerent metals, with nitric acid of medium con- 

 centration, will give products as below: 



KNaCaMg Al Zn Fe Sn Pb Hg Cu Ag Pt Au 



H 



H-,, NH3 NH3,N2, N2O N,0, XO XO, XO-, action. 



There may, of course, he secondary reactions, c./y , the re- 

 (.ixidation or some of the products by the nitric acid if this be 

 concentrated. As regards primary products of reduction, how- 

 ever, the conceptions already devek)ped may, in cv^njunction with 

 the law of mass action, help us to predict the general effect of 

 concentration of acid anrl accumulation of reaction i;rorlucts. Just 

 as nascent hydrogen can reduce nitric acifl to ammonia more 

 readily when at a high generation pressure than Avhen at a lower, 

 .so also nitric acid is more prnverful as an oxidising agent when 

 concentrated than it is when dilute. Ffence for a given oxidation 

 by nitric acid the concentrated acid will be reduced to a lesser 

 degree than will a dilute acid. For any given metal, then, wc 

 should expect dilute nitric acid to give a lower reduction prorluct 



