542 transactions of the american institute. 



Behavior of the Metal Lead and its Oxides with Reagents. 



Metallic lead is completely dissolved by nitric acid and water, forming 

 a clear colorless solution of nitrate of lead. 



By taking a solution of lead, obtaining either directly by the action of 

 nitric acid upon metallic lead, or by dis-^olving- sugar of lead in water, and 

 to the solution thus obtained, which to the eye, will, to all appearance, resent 

 ble water, and a few drops of sulphuric acid, immediately is formed a 

 white precipitate of sulphate of lead ; or-, if hiuriatic acid is employed, we 

 obtain a chloride of lead. Now both these precipitates are formed from the 

 acid coming in contact with the lead in solution, uniting with it, and form- 

 ing a nearly insoluble sulphate, or cliloride, as the case may be. 



Now the reason these tests are notsufficient to detect a small quantity of 

 lead, is, that though called insoluble, yet to a certain extent, in very large 

 quantities of water, it is soluble, and, therefore, will not precipitate ; for- 

 tunately, however, we have tests so extremely delicate that nothing more can 

 be desired, if due care is exercised in applying the reagents, and observing 

 the results ; and what still further adds to the certainty of these reactions, 

 is the great diversity of color obtained in the various precipitates formed 

 by different tests. 



First on the lists is sulphuretted hydrogen, either in the form of gas, or 

 liquid hydro-sulphuric acid, which is only a solution of the gas in water 

 and is so extremely delicate a test for lead that a black precipitate is formed 

 of the sulphide of lead, when this gas is applied to water containing lead 

 in solution, and when the quantity is so small that no visible precipitate is 

 formed, its presence is recognized by a brownish black color, imparted to 

 the water. 



If a solution of either the yellow chromate or red bichromate of potash \a 

 added to solutions of lead, a light yellow in the former, and an orange yel- 

 low precipitate in the latter case, will be produced. This, though a 

 characteristic, is not so delicate a test as sulphuretted hydrogen gas, or its 

 solution in water. Iodide of potassium produces a splendid yellow precipi* 

 tate. 



It may, as a general thing, be granted, subject to few exceptions, that 

 the same changes will be produced by the action of air upon metal, to a 

 greater or less degree, when exposed to the atmosphere for a long time, as 

 will be produced immediately by the atmosphere, if aided by the application 

 of heat to the melting point of the metal. It may, therefore, be useful to 

 observe the effect of a combined action of air and heat when applied to 

 lead. After removing the dross which has formed upon its surface during 

 the process of melting, we expose a metallic surface of almost silvery 

 brightness, but almost immediately this becomes dim and dull from the 

 formation of a sub-oxide of lead, and a mixture perhaps of metallic lead, 

 and oxide of lead, which floats on top of the melted metal ; now, remove 

 this as often as you will, and it is instantly replaced, and thus you can go 

 on indefinitely until all your lead is converted into this sub-oxide ; a dull, 

 ash-colored powder, which will now weigh as much more than the lead 

 originally melted, as it has absorbed oxygen from the air. Now, if this 

 Bub-oxide is again heated and exposed to the air, it will undergo another 



