ORGANIC MATTER IN STREAMS 



173 



total solids, we find that it rises in some of the tropical streams to 

 more than fifty per cent. The variation is shown in the following 

 table (Chvke-4:83): 



Tabic of Organic Matter in Various Streams in Percentages of the 



Total Solids. 



Danube 3.25 



James 4- 14 



Maumee 4-55 



Nile 10.36 



Hudson 1 1 . 42 



Rhine ii-93 



Cumberland 12.08 



Thames. 12.10 



Genesee 12 . 80 



Amazon 15-03 



Mohawk 15-34 



Delaware 16.00 



Lough Neagh, Ireland. .. . 16.40 



Xingu 20.63 



Tapajos 24. 16 



Plata 49-59 



Negro 53.89 



Uruguay 59 - 90 



In the tropical streams at the end of the list the high percentage 

 is due to the contributions formed by tropical swamps through which 

 they flow. Lough Neagh, Ireland, derives its organic matter in part 

 from peat bogs. 



Among the vegetable acids present are Humic acid (CooHjoOe), 

 Geic acid (CooH^.O,),* and Ulmic acid (C,oH,,Oe),* derived 

 from peat or soil richly charged with decaying vegetation. They 

 form various compounds or salts, such as ammonium humate, so- 

 dium and potassium humates, calcium humate, magnesium humate, 

 ferric humate, etc. The alkaline salts are easily soluble in water, but 

 those of the alkaline earths and metallic oxides are not soluble or 

 only with great difficulty, but these are soluble in aqueous alkalies, 

 especially ammonia and its carbonate. Humic acid itself dissolves in 

 8,333 parts of water at 6° C. and in 625 parts at 100° C. It is in- 

 soluble in water free from nitrogen or air. Among the products of 

 higher oxidation of these acids are the more soluble crenic acid 

 (C24H30O19 Wurtz), or Quellsaure, and apocrenic acid (C24H14O13 

 Wurtz), or Quellsalzsaure. The former occurs in the waters of 

 probably all springs, rivers, lakes, etc., and in rain water, rotten 

 wood, peat, and tilled soil, and in bog ore, ochre, etc. It is easily 

 soluble in water; its alkali salts (ammonium crenate, etc.) are, how- 

 ever, soluble to a less degree. Some of the salts of the alkaline 

 earths (calcium crenate) require much water, while others (mag- 

 nesium crenate) are easily soluble. The salts of metals are insoluble 

 (aluminium crenate, ferric crenate) or slightly soluble (ferrous 

 crenate, manganese crenate). Apocrenic acid also occurs in the 



* Formulas according to Mulder, others give different formulas. (See Julien- 

 17, 319-) 



