366 THE MUSCLE-TISSUE. 



ammonia it dissolves with great difficulty, so that it is possible to 

 precipitate the substance from its acid solutions by the addition of 

 ammonia. Silver nitrate precipitates the substance from its solu- 

 tions in nitric acid as a double salt, which dissolves in boiling nitric 

 acid, and crystallizes out on cooling in the form of fine needles. On 

 boiling a solution of guanin (as calcium compound) with acetate of 

 copper the corresponding salt is thrown down. 



Tests. Like xanthin, guanin gives the nitric acid reaction, but 

 with a somewhat more bluish-violet color, while Hoppe-Seyler's test 

 and that of Weidel are negative. With picric acid it combines to 

 form a yellow crystalline precipitate when a saturated solution of 

 the acid is added to a warm solution of the hydrochlorate. 



Adenin. Adenin crystallizes with three molecules of water in the 

 form of long hexagonal needles. If these are placed in an amount 

 of water which is insufficient for their solution and heat is now 

 applied to the temperature of 53 C., they suddenly lose their trans- 

 parency and become opaque. This peculiar behavior may aid in the 

 identification of the substance. It is soluble with difficulty in cold 

 water, more readily so in hot water, but is insoluble in ether. In 

 hot alcohol it dissolves to a slight extent. In acids and alkalies it 

 is soluble with ease. In ammonia it is less readily soluble than 

 hypoxanthin, but more readily so than guanin. From its alkaline 

 solutions the free base is precipitated by the addition of very dilute 

 acids, care being taken to avoid an excess. With silver nitrate it 

 forms a compound which is soluble with difficulty in boiling nitric 

 acid, and crystallizes out on cooling. Like the xanthin bases, that 

 have already been considered, it is precipitated from its solutions on 

 boiling with acetate of copper as a double salt. 



Tests. Like hypoxanthin, it does not give the common xanthin 

 reactions, nor does it react with zinc and hydrochloric acid. It is 

 most readily identified by the behavior of its crystals, as has just 

 been described, or by adding a solution of auric chloride to its 

 solution as a hydrochlorate, when a double salt is formed, which 

 crystallizes in part in octahedral or prismatic crystals, the angles of 

 which are often rounded off. 



Carnin. Carnin, as I have stated before, is not a true xanthin- 

 base, but is manifestly closely related to this group, as on oxidation 

 with bromine- water or with nitric acid it is transformed into hypo- 

 xanthin. Its formula and transformation into hypoxanthin are seen 

 in the equation : 



C 7 H 8 N 4 O 



Carnin. 



^4^3 -r 2Br : C^N^O.TIBr -f CH 3 Br -f CO 2 

 ruin. Hypoxanthin-brom- Methyl- 



hydrate, bromide. 



Its structural formula in its relation to hypoxanthin is seen below : 

 CH 3 .X CO HN CO 



CHOH C NH, HC C NH X 



^CH I \CR 



1 1 \_co_co N^ N C N^ 



