396 CHEMISTBT OF THE LEUGOMAINS. 



of dogs after feeding with caffein (Albanesi/ Kriiger ^). Kruger and 

 Schmidt' found it in the dog and rabbit after feeding with theo- 

 bromin (see p. 406, caffein). 



Before its discovery in urine this base had been prepared synthet- 

 ically by Fischer and Ach * out of 3-methyl uric acid in the same 

 way that theophyllin was first prepared from 1-3 di-methyl uric 

 acid. 



The free base is readily obtained from its salts which are dissoci- 

 ated on the addition of water or by addition of ammonia and evap- 

 oration to dryness. It forms a crystalline powder. From boiling 

 water it crystallizes in fine glistening needles, or in small obliquely 

 truncated prisms. From solution in alkali it is precipitated by 

 addition of acetic acid. 



When heated it turns yellow at about 360° and at higher temper- 

 ature it gradually decomposes without melting. It is soluble in 350 

 parts of boiling water (1—200, Albanesi), at 18° it is soluble in 1,110 

 parts of water (Albanesi). It is more difficultly soluble in absolute 

 alcohol, and still more so in chloroform and in acetic ether. It is very 

 easily soluble in dilute alkalis and in ammonia. Concentrated alkali 

 precipitates on cooling the sodium salt in the form of very fine bent 

 needles. On boiling with baryta it forms a very difficultly soluble 

 compound (1 : 8,924) which crystallizes in very thin, glistening, six- 

 sided plates. This fact distinguishes 3-methyl xanthin from 1-methyl 

 xanthin just as the solubility of the sodium salt distinguishes it from 

 7-methyl xanthin. 



The base forms with mineral acids crystallizable but unstable 

 salts. The chlorid crystallizes from warm acid solution in fine 

 needles. The iodid forms rather coarse prisms. The nitrate sepa- 

 rates from warm acid solution (1.16 sp. g.) as coarse irregular 

 crystals, and because of its difficult solubility it can be used for the 

 purification of the base (distinction from 1-methyl xanthin). 



On the addition of barium chlorid to an ammoniacal solution of 

 the base a precipitate forms which when dry dissolves in 480 (516) 

 parts of boiling water ; in 750 (862) parts of water at 18°. 



Silver nitrate added to a nitric acid solution of the base produces 

 a crystalline precipitate, largely consisting of needles which redis- 

 solve on heating and on subsequent slow cooling long, thin prisms 

 form. When silver nitrate is added to an ammoniacal solution of 

 the base it yields a white amorphous precipitate which is not altered 

 by heat. The base is thrown down by copper sulphate and sodium 

 bisulphite. 



On oxidation with chlorin it yields, like all xanthins, the murexid 

 test. 



MrcA. /. earn. Path. u. Pharm., 35, 449 ; Berichte, 32, 2280. 

 'Berichte, 32, 2818 (1899). 

 » Beiickte, 32, 2677. 

 ^Beriakle, 31, 1980 (1898). 



