€0 SUBSTJXCES SOLÜBLE IK DILUTE SODA. 



of soda) is sometimes a decomposition ])roäuct of metarabic acid or of 

 allied mucilaginous substances. The action of caustic soda on the 

 latter often results in the formation of products that are not pre- 

 cipitable by alcohol. But this body that thus remains in solution 

 on adding alcohol will be more often found to belong to the 

 albuminoids. (See § 235.) 



§ 108. Phlohaphene. — A brown residue insoluble in water would 

 frequently consist of phlobaphene. (See also § 48.) It should be 

 collected on a tared filter, Avashed, dried, Aveighed, and deducted 

 from the evaporation-residue in § 106 before the weight of the 

 substances derived from mucilage, caseine, etc., can be arrived at. 

 (See also § 246.) 



The p)ohjporic acid, isolated by Stahlschmidt,^ may also be 

 mentioned here. It is insoluble in water, ether, benzene, bisul- 

 l^hide of carbon, and glacial acetic acid, sparingly soluble in Avarm 

 chloroform, alcohol, and amjdic alcohol, but dissolved by dilute 

 ammonia, forming a Aaolet liqiiid, from AA'hich it is precipitated 

 by hydrochloric acid. It crystallizes in rhombic plates, and melts 

 at about 300\ 



^ Humus.' — I am convinced that the * humus ' mentioned in old 

 plant-analyses was in reality partly phlobaphene and its decom- 

 position-products. In the majority of vegetable substances 

 humus is not to be found, unless they are already in a state of 

 decomposition. Perhaps some thick barks and lignified fungi 

 might yield substances Avith characters resembling those possessed 

 by humus. To solvents such substances Avould, it is true, shoAv a 

 behaviour similar to that of the phlobaphenes ; but in distinguish- 

 ing them Ave may take advantage of the fact that the majority of 

 the so-called humic substances contain hydrogen and oxygen in 

 the proportion in Avhich they exist in Avater, and that humus does 

 not yield the decomposition-products mentioned in § 42 when 

 acted upon by fused caustic potash. 



^ Ann.ll. d. Chem. und Pharm, clxxxvii. 177 (1877) (Jonrn. Chem, Soc. 

 xxxii. G20). 



