56 SUBSTANCES SOLUBLE IN ALCOHOL. 



and resemble orange sulphide of antimony in colour. It should 

 not, however, be forgotten that albuminous and other similar 

 substances are also precipitated by this reagent. (Cf. § 232.) 



Polassw-cadmic iodide, obtained in analogous manner from iodide 

 of cadmium, gives white precipitates, which, like those yielded 

 by potassio-mercuric iodide, sometimes become crystalline. They 

 are mostly rather more soluble than those produced with the 

 latter reagent. 



Phmpho-molyhdic acid (a solution of the sodium salt in nitric 

 acid) yields with most alkaloids yellowish precipitates, which are 

 in certain instances rapidly reduced, and assume a bluish or 

 greenish colour. Ammoniacal salts and less complex amide- 

 compounds are also precipitated by this reagent. 



Metatungstic acid gives similar precipitates (§ 177). 



Chloride of gold yields yellowish precipitates with V€ry dilute 

 solutions of many alkaloids'. Sometimes a rapid reduction takes 

 place, and the yellowish colour changes to a reddish-brown, the 

 liquid itself occasionally assuming at the same time an intense 

 reddish tin (§ 1 86). I consider this reagent especially valuable 

 for our purpose, as ammoniacal salts and the less complex amides 

 are not precipitated by it. 



Perehloride ofplcUimmi, forms brownish-yellow precipitates with 

 most alkaloids (not all), hut is less valuable than chloride of gold, 

 because the precipitates are mostly more soluble, and because it 

 forms sparingly soluble compounds with ammonium and potassium 

 salts, etc. The precipitates obtained with this reagent also some- 

 times show a disposition to decomposa 



Mercwric chloride. — The white precipitates which this salt yields 

 with alkaloids are not very sparingly soluble, but it possesses 

 some value, as it does not precipitate ammoniacal salts, etc. The 

 same is the case with. 



Picric a-cidj which gives yellowish precipitates. 



Tannic acid, the compounds with which are usually of a greyish- 

 yellow or greyish-brown tint, and 



Bichromate of potash, which yields yellowish and occasionally 

 crystalline salts.^ 



'For group-reagents for alkaloids see further in my Ermittelung von 

 Giften, 2nd edition, 123; also Selmi, Jahresb. f. Pharm. 1874, 480; 1875, 

 341 ; 1876, 628 (Year-book Pharm. 1876, 110). For behaviour of cinchona- 

 alkaloids to sulphocyanide of potassium compare Schrage, Arch. d. Fhann> 



