General, perspicuous and readily applicable distinguishing charac- 

 teristics of these five groups are at present unknown; only the 

 determination, whether an organic body belongs to any of the 

 three first or any of the last two groups, that is, whether it is free 

 of nitrogen or nitrogenised, is as a rule easy, because nitrogenised 

 bodies mostly burn with a so-called horny odour and liberate 

 ammonia on application of alkalies. In dubious cases ignite the 

 body with sodium, treat the mass with water, add to the solution 

 subsulphate of iron and over-saturate afterwards with hydrochloric 

 acid, when in the presence of nitrogen a floccous turbidity of prus- 

 sian blue is produced. 



The investigation, to which of these five groups an organic body 

 belongs and in what proportions the elements stand to each other, 

 is moreover the object of the so-called elementary analysis ; con- 

 sequently the latter often extends into the province of special 

 phyto-chemic analysis, but, like ash analysis, needs not here to be 

 considered, since for their execution most text-books on organic 

 chemistry afibrd all the requisite instruction. 



2. With a mineral the object pointed out before can only be 

 attained by complete dissolution. The solution takes place either 

 in one or in several operations, in the latter case under change of 

 the solvent. As solvents serve mostly acids, not so frequently 

 alkalies, seldom water, never alcohol or ether. 



With a plant the determination of its constituents is likewise 

 ascertained by dissolution, but always with leaving a considerable 

 residue; and therefore this kind of solution belongs to those 

 operations, described by the term of extraction. The most im- 

 portant extracting agents are here ether, alcohol and water. Of 

 less importance are acids and alkalies. 



3. In a mineral analysis, the single constituents of the object of 

 examination are obtained either as such or in compoimds of 

 accurately known constitution, but always in proportions of 

 weight expressing most accurately the composition of the mineral. 



In a phyto-chemic analysis means for a precise separation of 

 the constituents are often still wanting. Quantitative determina- 

 tions often encounter invincible difficulties, can only, in com- 



