284 



a substance, though in both these cases it is not superior to 

 sulphuric acid, and is therefore used less frequently. 



After the acids, caustic alkalies must be applied; liquor of 

 ummonia, of 0'960 specific gravity, potash or soda-ley, of 1*15 

 specific gravity. They are destined for solving purposes, some- 

 times aided by a gentle heat. Should the substance have been 

 dissolved in any of the three alkalies, and should diluted acids 

 have proved unable to dissolve the same substance, then yet has to 

 be tried, whether the alkaline solution on over-saturating with an 

 acid will throw down the substance again or not. In the first 

 case no alteration has been effected by the alkali; in the latter 

 case a change has taken place. It may also happen that the 

 alkaline solution becomes turbid on diluting with water, or even 

 on adding a fresh portion of the alkali. In the latter case what 

 has been separated is not the oi-iginal body, but a compound of it 

 with the alkali, and insoluble in alkaline liquids. In dissolving 

 nitrogenised, especially protein substances in fixed alkalies, appli- 

 cation of heat must be avoided entirely or as much as possible, in 

 order to prevent decomposition, mostly connected with the evolu- 

 tion of ammonia. 



The other liquids, the influence of which on the dry substance 

 may be tried also, and which act only as solvents, are ether, alcohol, 

 toater, benzol, chloroform, wood-sjnrit, sulphide of carbon, petroleum, 

 oil of turpentine ; but the resulting solutions are only available for 

 testing with other chemicals after the solvents, as ether, alcohol, 

 benzol, etc., have been removed and are replaced by water. 

 Their further treatment must be referred to the following sub- 

 division : — 



B. — Examination of the Substance in Solution. 



Under this head are comprised not only the liquids obtained 

 in the coiirse of the analysis, as well as the solutions of the solid 

 substances obtained in the same way, and dissolved either in 

 water or in diluted acids or in alkalies, biit also the extracts 

 obtained by means of ether, alcohol, water, diluted acids and 

 alkalies. The three last-named solutions are submitted dh-ectly to 

 the action of reagents, the alcoholic or ethereous solutions only, 

 after the respective solutions have been removed by evaporation 

 or distillation and replaced by water. By this change of the ether 

 or alcohol by water the resulting aqueous solution will seldom be 

 clear, but mostly turbidified by substances insoluble in water, to 

 be separated by filtering, and to be submitted to a special ti-eat- 

 ment (specified in Division III.) Siich solutions, obtained by 

 treatment with water from the alcoholic and ethereous extracts, 

 often retain dissolved, through the influence of other constituents, 



