THE USE OF LIQUID AMMONIA AS A SOLVENT 113 



ammonia has no basic properties whatever. A solution of 

 potassium amide in ammonia possesses the power of reddening 

 an ammonia solution of phenolphthalein and when added to 

 ammonia solutions of metallic salts precipitates compounds 

 analogous to the basic oxides. Thus, with silver nitrate it 

 3'ields silver amide as a very explosive white precipitate : 



AgNO :j + KNHj = ppt.AgNH, + KNO*. 

 AgN0 3 + KOH = ppt.AgOH + KNO,. 



Similar compounds are formed when a solution of the alkali 

 amide is added to ammonia solutions of mercury iodide, lead 

 nitrate and lead iodide but in these cases intermediate products, 

 corresponding to basic salts, are first formed. These indications 



point to the conclusion that the NH 2 ion in ammonia is analogous 



to the OH ion in water. We should then expect to find that the 



hydrogen ion had acid properties in ammonia, just as in water. 



Ordinary acids cannot be dissolved as such in liquid ammonia 



but they can be in the form of their ammonium salts and it is 



+ 

 then found that these substances behave as acids, the NH 4 ion 



+ 

 behaving in an analogous manner to the H ion in water. 



The following properties of ammonium salts indicate the 



acid nature of their solutions in liquid ammonia : — 



(1) They discharge the colour of an ammonia solution of 

 phenolphthalein to which a little alkali has been added. 



(2) They dissolve metals such as sodium, potassium, 

 magnesium and calcium, hydrogen being evolved. 



2M + :NH,X = 2 MX + 2NH3 + H,. 



(3) Basic salts and metallic oxides which are insoluble in 

 ammonia are soluble in solutions of ammonium salts : 



CaO + 2NH.NO, am ' = Ca(NO,). am + H 2 + 2NH». 



Substances like these, which behave as acids in ammonia 

 solution, are termed ammono-acids by Franklin (13) ; the corre- 

 sponding bases and salts are designated ammono-bases and 

 ammono-salts. This nomenclature is convenient and saves the 

 repetition of phrases and therefore will be used in the rest 

 of this account. 



1 The symbol (am) means that the substance is in solution in ammonia just as 

 aq means that it is in aqueous solution. 



8 



