140 MUSCULAR TISSUE. 



in boiling HNO 8 , sp. gr., 1.1., to which a little pure urea has been 

 added to prevent the decomposition of the bases. While hot, filter 

 from a small amount of AgCl, which may remain, then allow to 

 stand twelve hours. Hypoxanthin-silv&r nitrate separates in small 

 needle-shaped crystals. Filter and wash with water. From the 

 filtrate, by the addition of an excess of ammonia, is obtained a 

 slight precipitate of wantMn-silver oxid. The free xanthin and 

 hypoxanthin may be obtained by suspending their silver com- 

 pounds in water and, after heating and making slightly alkaline 

 with ammonia, adding ammonium sulphid drop by drop until the 

 silver is precipitated, avoiding an excess. On evaporating the 

 filtrate the xanthin and hypoxanthin will be left as microscopic 

 crystals. 



Most of the guanin is left in the precipitate made by the am- 

 monium sulphid. It can be dissolved by boiling with a little very 

 dilute hydrochloric acid. Filter and precipitate it from the filtrate 

 by making it alkaline with ammonia. 



To obtain the lactic acid from the filtrate from the precipitated 

 hypoxanthin, etc., first precipitate the silver by HjjS and filter. 

 Concentrate the filtrate on the water-bath until most of the am- 

 monia has been expelled. Then cool and acidify strongly with 

 dilute sulphuric acid. The lactic acid is thus set free and can 

 now be separated by shaking gently with about one-fifth of its 

 volume of ether, which dissolves the lactic acid, but not the 

 sulphuric. After shaking in a glass-stoppered funnel, allow it to 

 stand until the ether has all risen to the top of the liquid. Then 

 draw off the water and the ether into separate flasks. Repeat the 

 operation a few times with fresh portions of ether. Mix the differ- 

 ent portions of ether and distill or evaporate it. The residue con- 

 tains the lactic acid mixed with a little sulphuric. Dilute with 

 water and boil a minute with zinc carbonate until it has lost its 

 acid reaction. Filter, and evaporate the filtrate on the water-bath 

 to a small volume. Then let it stand, and the zinc lactate will 

 crystallize in four-sided prisms: (C 8 HA) 2 Zn + 2H 2 O. Filter 

 these from the remaining liquid, and dry on filter-paper. 



To obtain the free acid dissolve some of the crystals in water 

 and precipitate the zinc with hydrogen sulphid gas. Filter, and 

 evaporate the filtrate. The acid will be left as a syrupy liquid. 

 Test it for its acid reaction and sour taste. It differs from fer- 



