56 SUBSTAXCES SOLUBLE IX 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.) 



Pofassio-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. 



Fhos2)ho-violi/hdic acid (a solution of the sodium salt in nitric 

 acid) yields vnth most alkaloids yellowish jjrecipitates, 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. 



McMungstlc acid gives similar precipitates (§ 177). 



Chloride of gold yields yellowish precipitates Avith very dilute 

 solutions of many alkaloids. Sometimes a rajnd reduction takes 

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

 liquid itself occasionally assuming at the same time an intense 

 reddish tint (|^ 186). I consider this reagent especially valuable 

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

 are not precipitated by it. 



Perchloride of platimnn forms brownish-yellow precipitates with 

 most alkaloids (not all), but 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 decompose. 



Mercuric chloride. — The white precipitates Avhich this salt yields 

 with alkaloids are not very sparingly soluble, 1)ut it possesses 

 some vahie, as it docs not precipitate ammoniacal salts, etc. The 

 same is the case with 



Picric acid, which gives yellowish i)recipitates. 



Tannic acid, the compounds with which are usually of a grcj'ish- 

 ycllow or greyish-brown tint, and 



Bichromate of 2>ofash, which yields yellowish and occasionally 

 crystalline salts. ^ 



^ For group-reagents for alkaloids see further in iny Ermittelung von 

 Giften, 2nd edition, Vl'.i ; also Selnii, JahrcHb. f. Pharm. 1874, 480; 1875, 

 341 ; 187G, 628 (Year-book Pharm. 1876, 110). Tor behaviour of cinchona- 

 alkaloids to fiulphocyanide of iwtassium compare Schräge, Arch. d. Pharm, 



