OF ARTS AND SCIENCES. 



91 



was slightly warmed ; the air thereby driven out was of course re- 

 placed with quicksilver, the upper surface of which, after the original 

 temperature had been reestablished, was marked. Now, if any decom- 

 position of common salt occurred by the agency of lead, the chlorine 

 would be freed from the sodium, the sodium would decompose the wa- 

 ter, hydrogen would be set free, and the column of mercury depressed. 

 Instead of any such result, the column of mercury regularly rose in ev- 

 ery instance. An apparatus of this description, several months in ac- 

 tion, is still preserved in my laboratory. It might still have been said, 

 that, had the flask been deprived of air, the lead would have been acted 

 on by the simple chloride. The experiment of lead and sea-water, in 

 a flask deprived of air, has been made. The flask was sealed on the 

 25th of May last. The bar for a long time retained its perfect bright- 

 ness, and is but very faintly dimmed at this late day, February 1, 

 1849. 



" 5. Action of Organic Matter. — It has been conceived that or- 

 ganic matter might exert a deleterious influence. Experiments already 

 recorded (p. 15) show that the presence of organic matter increases the 

 protecting power of water which is to be transmitted through lead. If 

 the quantity exceed one ten-thousandth of the weight of the water, pre- 

 cipitates of oxide of lead, united to organic matter, take place. Orfila 

 has remarked the precipitation of the coloring matter from Burgundy 

 by neutralizing it with litharge.* Its influence in withdrawing the 

 oxygen from solution has also been alluded to. In the important re- 

 searches of Dr. Smith f upon the air and water of towns, it is men- 

 tioned that the presence of nitrates in the London water prevents the 

 formation of organic matter, and that organic matter, in filtering through 

 soils, becomes rapidly oxidated. Additional experiments bearing upon 

 this point are recorded farther on. 



" Influence of Impurities in Water. — It is a prevailing conviction, 

 that the more impure a water is, or, in general terms, the more salts it 

 contains in solution, the less will be its action on lead. The influence 

 of sulphate of magnesia (epsom salts) and chloride of sodium (com- 

 mon salt) in distilled water was the subject of experiment. The ac- 

 tion, it will be seen, was more vigorous in distilled than in the impure 

 waters. 



* Toxicologie Gendrale, Vol. I. p. 616. t Proc. Brit. .^ss. Mhen., No. 1087. 



