WATRR. J»39 



tempexature diminishes. Thus it is that the water of a pond or lake 

 freezes at the surface, while it preserves beneath a teinpoiature 

 some degrees above 32°. In a situation where the temperature of 

 the air was 29", Davy found the thermometer indicate 43" in the 

 herbage of an iimndated meadow completely covered with ice.* 



Water is always impregnated with atmospheric air, and a minute 

 quantity of carbonic acid. Deprived of air, it is not agreeable to 

 drink ; it is even said, when long continued, to prove unwholesome 

 if the dissolved gases are expelled by ebullition. River- water usual- 

 ly contains j'^th in volume of air, and T^^th carbonic acid. In spring- 

 water, the amount of the latter is sometimes far more considerable. 



The quantity and nature of saline ingredients in drinkable water 

 vary much : in an agricultural point of view, the study of the con- 

 tained salts would certainly be useful. The waters which serve as 

 drink to the cattle of a farm, introduce into the dung-heap all the 

 matters which are dissolved or held in suspension. At Bechelbronn, 

 for example, I find that more than 2 cwts. of alkaline salts get into 

 the dung in this way every year. When a farmer has the choice of 

 several waters for giving his cattle or irrigating his meadows, he 

 will do well to select that which is richest in alkaline salts, and still 

 good to drink. In the steppes of America, it is astonishing with 

 what discernment the cattle choose waters for allaying their thirst, 

 containing minute quantities of sulphate of soda or common salt. 



I close these considerations with a tabular view of the most recent 

 analyses. The quantities of salts put down have been deduced from 

 100,000 parts of water for drinking. 



* Davy, Agricultural Chemistry, p. 353 



