382 CHEMISTRY OF THE LEUCOMAINS. 



bines with four of guanin. The trivalent ferricyanic acid does not 

 always exist as such in combination, as in the case of the salt of 

 guanin. On the other hand, as pointed out by Wulff, guanin, 

 though usually a monacid base, may unite with different proportions 

 of acid. Thus four nitrates are known, while in the oxalate and 

 tartrate three molecules of guanin unite with two molecules of acid. 



Guanin also forms a compound with ferrocyanic acid, which ap- 

 pears as almost colorless needles. 



Guanin nitroferricyanid, (C5H5NpX-H2NOFe(CN)5 + liH^O. 

 This is likewise obtained by adding sodium nitroprussid to a solu- 

 tion of guanin hydrochlorid. It forms large, glistening, brick-red, 

 four-sided prisms with pointed ends. 



Potassium bismuth iodid produces in even very dilute solution of 

 the salts of guanin a precipitate which consists of fine, rather long 

 red needles. When dry it forms a loose, deep-red mass. On heat- 

 ing even below 100° water is given off and the color changes to a 

 dark violet. It dissociates readily on contact with water. The 

 formula as determined by Wulff is C5H5Np.HI.2Bil3 + 2Hp. 



Guanin picrate, C^B.^^fi.CJS-l^O^piL + H^O. The reaction 

 with picric acid (Capranica) is said to be very characteristic, and a 

 means of distinguishing this base from xanthin and hypoxanthin. 

 It is best obtained by adding a cold, saturated solution of picric acid 

 or of sodium picrate to the warm acidulated solution of guanin when 

 a light, crystalline precipitate forms. Under the microscope it appears 

 in pencil-shaped, fern-like tufts of fine, orange-yellow needles, rarely 

 in bunches of large needles. Adenin picrate has a lighter color. 

 This compound is characterized by its crystalline form and its ex- 

 treme insolubility in cold water and in dilute acids. Guanin solu- 

 tions, 1 : 30,000, are still precipitated by picric acid, though after 

 some time. When dry it has a golden-yellow color, felt-like con- 

 sistency, and silky luster. On heating it becomes almost orange-red, 

 and on cooling the original color returns. At 110° it loses water of 

 crystallization, the silky luster, and becomes light-yellow; at 190° 

 it begins to decompose. It dissolves easily on warming in fixed 

 alkalis and carbonates. A solution of guanin-sodium is therefore 

 precipitated only by excess of picric acid. It is rather easily soluble 

 in warm dilute acids ; difficultly in cold acids. It is dissociated by 

 water, alcohol, and ammonia, especially when warmed (Wulff). 



Guanin silver picrate, Q^J^gSfi.C^^i^O^fiB. -f IfH^O, is 

 thrown down from a boiling solution of a guanin salt, treated with 

 excess of picric acid, by silver nitrate as a voluminous, lemon yellow 

 amorphous precipitate. It is very difficultly soluble in hot water, 

 almost insoluble in cold water. It tends to become dissociated on 

 contact with water — picric acid being removed. Ammonia removes 

 the picric acid easily and completely, leaving guanin-silver (Wulff). 



Guanin sodium dissociates on contact with water. 



