305 



If a peculiar penetrating odour should be evolved by the caustic 

 alkali, a volatile alkaloid may be present; the examination of 

 which must be deferred to section X. 



Carbonate of potash or of soda. — In the main, all that has been 

 said of the preceding test applies to this also. 



Solution of baryta. — It causes, like the alkalies, darker tints in 

 the liquids and eventually it precipitates. The precijiates may 

 be not only alkaloids and alkaline earths, but also compounds of 

 the reagent with sulphuric, phosphoric, organic acids, and with 

 acid-like bodies as pigments and resins. A closer investigation of 

 such a precipitate is not advisable here on account of its complex 

 nature. 



Of more importance than solution of baryta is lime-water. It 

 is similar in its effects to the alkalies, though not so energetic, and 

 prodvTces either a darker colour or turbidness, the latter being 

 also indicative of a series of acids the compounds of which with 

 lime are insoluble or sparingly soluble in water. Consequently 

 a tiu-bidness, pi'oduced immediately after adding the test, may 

 prove the presence, irrespective of phosphoric acid, of oxalic, 

 tartaric, tannic, and other acids, and is oxalic acid, if the turbid- 

 ness does not disappear with acetic acid. — Filter off the precipi- 

 tate, obtained by lime-water in excess, and heat the filtrate to the 

 boiling point ; a cloudiness, which disappears on cooling, indicates 

 citric acid. If neither cold nor hot a turbidity is obtained ; acids 

 may be present which yield such compounds with lime as are 

 soluble in water, as for instance malic, quinic, lactic acids, and 

 which will come under notice in the course of the analysis. 



Chloride of calcium, — A turbidness obtained by it indicates 

 oxalic acid, if not removable by acetic acid. If it dissolves in the 

 latter, it may have been occasioned by phosphoric acid, but in 

 this case the acetic acid has to be added immediately, as else the 

 precipitate would become crystalline and almost insoluble in acetic 

 acid. 



Chloride of iron. — The altei-ations effected by this test consist 

 mostly in the production of various colours (with or Avithout 

 turbidness), to recognise which the mostly dai'k liquid must be 

 diluted so far as to be of only a slightly yellowish coloui-. A 

 green colour, obtained with the test, indicates iron-greening, a 

 blue or violet colour an irmi-blueing tannic acid. If these 

 acids are not present in too small quantities, colovired preci- 

 pitates are also obtained, though sometimes of such a mixed 

 colour as to appear brown instead of gx'een, and grey instead of 

 blue. 



Gallic acid yields, with chloride of iron, a reaction similar to 

 that of gallotannic acid, but the gallate of ii'on is abundantly 

 soluble in acetic acid, in the hydrates, and in the carbonates of 

 alkalies, this being not the case with gallotaniiate of iron. 



