OF ARTS AND SCIENCES. 



89 



present, oxygen will be given out and immediately expelled, until the 

 maximum of the solvent power for air by the given temperature be at^ 

 tained. 4th. On the withdrawal of sunlight and the reduction of the 

 temperature, the animalculae cease to evolve oxygen, and that which is 

 in solution becomes the prey of the decaying organic matters present. 

 5th. The hydrogen of organic bodies (as Liebig has remarked) oxidates 

 first. This position I have verified by a series of observations, to which 

 I will here only refer. 



" The following experiment may be mentioned in this connection. 

 Two clear glass globes of about four and a half inches in diameter, 

 filled with waters from two wells in Cambridge, in one of which, after 

 rest of twelve hours in leaden pipe, lead was detected, and in the other 

 of which, after equal exposure, no lead was recognized, were placed in 

 a window of south-southeast exposure. Into each globe a skein of silk 

 weighing 1.25gr. was introduced ; at the end of five days, the quantity 

 of gas evolved was more than twice as great in that containing the well- 

 water that acted on lead as in the other. No admeasurement of the 

 quantity was attempted, for the following reason : I wished to know 

 what would become of these gases, — the water containing organisms 

 which must soon consume their supply of nutriment. In a period equal 

 to the above, the gases were entirely absorbed, and after the lapse of a 

 month, during which time there were several days of brilliant sunshine, 

 no gases appeared. An isolated experiment of this description cannot 

 have much value. But it seemed to me worth recording, as sustaining 

 what Liebig has remarked, that of the elements of organic bodies the 

 hydrogen is more readily oxidated than the carbon, and as illustrating 

 the decay of organic bodies in water. 



" Of the various popular reasons why lead should not be employed 

 for distributing water, the following have been found not to be sustained 

 by experiment or authority. 



" 1. The Galvanic Action of Iron and Lead. — The efTect of con- 

 tact with iron, in most of its points of view, has been investigated. In 

 diluted acids, Iright lead in contact with iron is positive, — coated lead, 

 negative. Yorke. — Diluted acid faciUlates the solution of iron in con- 

 tact with lead. Runge. — In strong nitric acid, iron, in connection with 

 lead, is positive. Delarive. — In potash solution or lime-water, bright 

 lead is positive to iron, but oxidated or coated lead is negative. This 

 is also true of these metals m a solution of saltpetre. Yorke. — It is 

 also true in a solution of sal-ammoniac. Wetzlar. — Thus in acid, al- 



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