98. ESTIMATION OF AMIDO-COMPOUNDS, ETC. 83 



etc., thus liberated, yield with perchloride of platinum double salts 

 ( 183) that are soluble in ether-alcohol, and error may therefore 

 be frequently avoided by precipitating a second portion of the 

 distillate with excess of perchloride of platinum, evaporating on 

 the water-bath, extracting the residue with ether-alcohol, drying 

 and weighing instead of titrating the excess of acid with an alkali. 

 If both experiments yield the same result it may be concluded 

 with tolerable certainty that no amides, or only traces, are present. 

 If the estimation by the first method gives a higher result than 

 that by the second, the former is to be regarded as the more 

 accurate, and the excess noted as amido-compounds, etc. If, on 

 the other hand, the estimation by platinum is higher than that 

 by titration, the presence of an amide forming a double platinum 

 salt insoluble in ether-alcohol and of a higher molecular weight 

 than ammonia would be indicated. In the method of deter- 

 mining ammonia described in 97, b, certain chlorides of amines 

 and alkaloidal substances, as for instance coniine and nicotine, 

 would be almost completely volatilized, and thus escape esti- 

 mation. 



The separation of ammonia from many amines may frequently 

 be effected by taking advantage of the difference in solubility of 

 the chlorides, sulphates, and oxalates of the respective bases in 

 alcohol. In preparing larger quantities of the base for closer 

 investigation, the material might be distilled with magnesia or 

 lime (97 a), the distillate received in one of the above-mentioned 

 acids, and evaporated to dryness on the water-bath. The residue 

 might be extracted with alcohol, the solution again evaporated 

 to dryness, and the distillation with alkali repeated, if possible, 

 in a current of hydrogen. (Cf. 239.) 



99. Nitric Acid. For the estimation of nitric acid another 

 portion of the aqueous extract of 71 is taken and treated by 

 Schulze's 1 or Wulfert's 2 method. 



Schulze directs the liquid to be treated first with pure potash, as 

 long as ammonia is evolved, then with permanganate of potassium 

 (free from nitrate) till the colour is permanent after ten minutes' 

 boiling. Excess of permanganate is removed by formic acid, the 

 solution neutralized with pure sulphuric acid and evaporated to 

 about 10 cc. This is then introduced into the flask A of the 



1 Zeitschr. f. anal. Chem. vii. 392. 



2 Landw. Versuchsstationen, xii. 164. 



62 



