122 THE SIMPLER NATURAL BASES 



with organic bases. The reagent is prepared by dissolving 80 grm. of 

 bismuth subnitrate in 200 c.c. of pure nitric acid of density n8, and 

 pouring this solution slowly, with stirring, into a concentrated aqueous 

 solution of 227 grm. of potassium iodide. A precipitate forms and 

 dissolves on stirring to a deep orange solution. This is cooled strongly 

 to allow potassium nitrate to crystallise out as far as possible. The 

 clear solution is poured off and made up to I litre; the more concen- 

 trated solution may also be employed. The reagent should be kept 

 in the dark. Kossel and Weiss [1910] recommend a solution of 50 

 grm. sodium iodide and 100 grm. bismuth iodide in 100 c.c. of 0*5 

 per cent, aqueous hydriodic acid. 



To regenerate the bases, the precipitate caused by addition of 

 Dragendorff's reagent is ground up with freshly precipitated lead 

 hydroxide, which is transformed to lead oxyiodide. After filtration 

 the last traces of lead are removed by hydrogen sulphide ; the solution 

 is then concentrated to a syrup, which is extracted with alcohol. 



To precipitate bases as periodides a concentrated solution of iodine 

 in potassium iodide is employed (compare the estimation of choline 

 and betaine by Stanek's method). The periodides may be decomposed 

 by sodium bisulphite or thiosulphate, but this introduces into the solu- 

 tion a good deal of inorganic matter. It is better to grind up the per- 

 iodide in warm water with finely divided copper, so-called " molecular 

 copper," prepared by Gattermann's method, as follows : Zinc dust is 

 added through a sieve to a cold saturated solution of copper sulphate 

 in a porcelain dish, until the solution is only faintly blue. The pre- 

 cipitated copper settles down and is repeatedly washed by decantation. 

 To remove traces of metallic zinc, the copper is placed under several 

 times its volume of distilled water and quite dilute hydrochloric acid 

 is added until no more hydrogen is evolved and the copper is no longer 

 carried up to the surface of the solution but remains quietly at the 

 bottom. The copper is then collected on a filter at the pump, washed 

 until neutral and kept in a well-stoppered bottle in the moist state. 

 It is very easily oxidised. 



For the isolation of individual bases from the fractions obtained 

 by any of the above methods, it is necessary to prepare a crystalline 

 derivative. Benzoylation is occasionally resorted to (in the case of 

 diamines from urine, p-hydroxyphenyl-ethylamine, etc.) but generally 

 a salt of the base is crystallised. The hydrochlorides of putrescine and 

 of betaine are almost insoluble in alcohol, in contradistinction to the 

 corresponding cadaverine and choline salts. The nitrates of some 

 bases (guanidine, methylguanidine, arginine, hypaphorine, certain 



