74 



THK FARM WATER SUPPLY 



upper level of the standing ground water is commonly called 

 tiie water-table, and is somewhat higher than the surface of 

 nearby ponds or quiet streams, the height var>ing with the 

 shape of the land, the kind of soil, and the dryness of the sea- 

 son. 



The proportion of matter, which the ground water will have 

 in solution, depends upon the quantity of soluble sui)stances 

 with which it came in contact during its passage from the 

 clouds, through the air and soil, and the amount of dissolved 

 material that plant-roots will absorb as the water percolates 

 among them. 



This soluble matter consists of both organic and mineral 

 substances and is determined by evaporating a measured quan- 

 tity of water to absolute dryness and weighing the residue. In 

 M'aters from localities atibrding no opportunity for pollution 

 from dwellings or barn-yards, we have found less than lo 

 parts of solid residue from 100,000 parts of water, while in 

 waters from polluted sources we have almost always found a 

 much larger amount. B}' carefully burning the total residue, 

 the organic matter is destroyed and the mineral matter deter- 

 mined by weighing the fixed residue. Following are some re- 

 sults which substantiate what has been said about the naturally 

 insoluble nature of New Hampshire rocks: 



RESIDUES FROM UNPOLLUTED GROUND WATERS. PARTS IN 100,000 



Locality. 



Total 



solid 



residue. 



Fixed 

 residue. 



Locality, 



Total 



solid 



residue. 



Fixed 

 residue. 



Durham 



Durham 



Durham — 

 Newmarket 

 Northwood 



8.20 

 9.80 

 9.40 

 5.80 

 6.80 



5.40 



4.80 



2.90 



Hillsborough 



Meredith 



Wakefield.... 



Tamworth 



Ashland 



6.20 

 5.60 

 4. SO 

 5.00 

 4.40 



4.40 

 4.20 

 2.20 

 3.20 



Similar results have been obtained in Massachusetts. Ac- 

 cording to the Report of the Massachusetts State Board of 

 Health for 1S91, page 356, twenty-two unpolluted springs 

 yielded water with less than ten parts of solid matter dissolved 

 in 100,000 parts of water. 



