OF ARTS AND SCIENCES. 85 



of lead, the oxide of lead is dissolved, while the carbonate of lime is 

 df posited.' * If with the aid of heat such decomposition results, it 

 might be conceived that, favored by the nascent condition, quantity, 

 and time, there might be to some small extent a corresponding decom- 

 position. The first was the principal experiment bearing on this point 

 made at the date of my last letter to the Water-Commissioners, and up- 

 on this experiment, and the known solubility of the nitrate, I ascribed 

 the increased action of water consequent upon the addition of nitrates to 

 a slight double decomposition. It had been ascribed by Dr. Danat to 

 the conversion of the protoxide of iron, in solution as protosulphate, in- 

 to the peroxide, by which he conceived there would be free sulphuric 

 acid, and therefore free nitric acid, in water containing protosulphate of 

 iron and nitrates. | This explanation would not apply to the action of 

 neutral waters, or of those containing no protosalts of iron, though ni- 

 trates were present. The whole subject has undergone a more thor- 

 ough eixamination. The conclusion that nitrates are not reduced by 

 lead I have found to be erroneous ; for experiment has shown that up- 

 on boiling a strong solution of nitrate of potash to expel the air, and in- 

 troducing a bar of bright lead, it became immediately coated with sub- 

 oxide of lead, and this without the evolution of gas. There had been 

 a partial reduction of the nitric acid. Upon testing the solution with 

 hydrosulphuric acid, it gave, after long digestion, but a faint discolora- 

 tion. Upon pouring off the liquor and adding to it oxide of lead, and 

 continuing the digestion, a large quantity of lead was dissolved, which 

 in 66cc. gave of sulphide of lead 0.0106gr. = 0.7296gr. in a gallon. 

 The solution reacted strongly alkaline. As the only known inorganic 

 salts of nitrous acid are its compounds with lead, it was probable that, 

 upon the reduction of the nitric acid to nitrous acid, it had abandoned 



* " Lorsqu'on fait bouUir du nitrate calcique avec du carbonate plombique il se 

 dissout de I'oxyde plombique taudis que le carbonate calcique reste." — Traite dc 

 Chemie, 1847, Tom. IV., p. 91. 



t Report of the Joint Special Committee of City of Lowell, Aug., 1842, pp. 8-11. 



t The change that takes place when a solution of copperas is exposed to the air 

 may be thus represented : — 4 (Fe 0, S03) + 20 = Fea O3, 3 S O3 -|- Foq O3, S O3. 

 The latter compound is insoluble in water. Gmelin. — The constitution of the pre- 

 cipitate, according to Mitscherlich and Scheerer, is 2 Tea O3, S O3-J- 3 H O. 

 WiTTSTEi N (Buck. Rep., 3 R., Bd. I., S. 182 - 189) gives it as 2 Fe. O3 -f 3 S03 -f 

 8 H O. An acid salt remains in solution, which is probably what Dr. Dana wonid 

 have understood from the statement that tiic above decomposition produces free 

 sulphuric acid. ^ 



