283 



in a glass tube of at least l-24tli inch diameter, and closed at the 

 bottom. The non-volatility is now characterised by a dis- 

 colouration (blackening), and by the evolution of empyreumatic 

 vapours, which must be tested as regards theii- acid or alkaline 

 reaction by both litmus and turmeric paper, inserted into the 

 upper part of the tube. A brown colouration of the turmeric paper 

 indicates with certainty a nitrogenised substance (proteinoid), 

 and therewith is always connected an unpleasant odour like that 

 of burnt horn or feathers (so-called hoi-ny odour). If the 

 ttxrmeric paper remains unaltered, then the substance contains 

 either no nitrogen or only a little of it, and in this case the 

 litmus paper assumes a red colour. 



After the substance has been tried on its behaviour towards, 

 heat, it is next exposed to the action of inineral acids, and first to 

 that of concentrated sulphuric acid, which may efiect alterations of 

 colour, solutions, or odours. Warming the substance with it 

 woidd only be advisable, if no perceptible alteration takes place in 

 the cold; else a carbonisation would be the result. The solution 

 thus obtained becomes sometimes turbid on addition of water, as 

 it may throw down the substance altered or unaltered. — Diluted 

 with 5 to 10 pai-ts water, the sulphuric acid serves as reagent 

 of glucosids, as it possesses the property of sepai-ating these after 

 some time on warming, and to convert the cai-bo-hydrate contained 

 in the gl^icosid into sugar, which is recognised by the formation of 

 red suboxyd of copper on wai'ming, after the acid has been 

 neutralised by excess of soda, and mixed with dissolved alkaline 

 tartarate of copj^ei-. — In a still more diluted state (1 : 50 or 100) 

 the sulphuric acid may be used for indicating the alkaloid-nature 

 of a substance, inasmuch as the latter dissolves more readily in it 

 than in pure water. 



Nitric acid, in a moderately concentrated state (from 1 "3 specific 

 gravity upwards), acts almost always decomposing (oxydising) 

 on dry substances, under the simultaneous appearance of yellow- 

 brown fumes, accompanied, in most instances, by a coloiiration of 

 the acid, by a change of the colour of the substance, or by a 

 solution of the latter. Exposed to the heat, even a weaker 

 acid shows already oxydising efiects, and evolves brown-yellow 

 vapours. Very diluted, it may be used instead of sulphuric 

 acid; in great dilution, for indicating the alkaloid nature of 

 a substance. 



Concentrated hydrocholoric acid (of 1*16 to 1*20 specific gravity) 

 acts least energetically of these three mineral acids, but produces 

 sometimes a characteidstic colouration of the substance, or gives a 

 specific odour after a solution has been efl^ected, and therefore it 

 should be used in every case. — Diluted with .5 to 6 parts water 

 it may be used, like sulphuric acid, for the discovery of glucosids ; 

 and still more diluted, it may indicate the alkoloid-nature of 



