298 OXIDATION OF LEAD. 



a. pellicle of a brilliant white, which appears to be nothing 



but carbonate of lead. 



May be kept If kept under water, this oxide of lead undergoes no 

 under water ., , , & 



uachanged, perceptible change, whether it be exposed to the light, or 



defended from it. But if it be kept ever so little time in a 



but exposed to flint glass phia! with a little water only, it is found to attach 



becSis'yel- itself to the sides of the P hlal above the surface of the 

 Jow, and then water; and if the phial be exposed to the rays of the sun, that 

 portion of oxide acted upon by the light changes successively- 

 from white to yellow, and from yellow to red, tftus furnish- 

 ing massicot and minium. 

 Changed to If the white oxide be placed over a fire in a glass capsule 



^Eumby nd !t chan S es in a short tim e, ' from white to yellow, and from 

 heat. yellow to red, like that exposed to light. 



Easily and This oxide may be manufactured in quantity, and at little 



cheaply manu- , , ,, „ • 



faetured. expense, so as to lessen the cost of certain preparations in 



which it may be employed. It may likewise.be used as it is 



in painting. 



Method of The following is the method I have employed to obtain 



making it. this oxide. In a leaden barrel I enclose a certain quantify of 



small shot, with as much water as equals about one fifth of 



its capacity, leaving the rest full of air. This barrel is 



turned round by means of an axis fastened to each end. 



It is obvious, that it might easily be kept in continual motion 



by a stream of water. 



To renew the air in the barrel, I introduce leaden 



tubes at various parts of its circumference, soldered to the 



sides so that no water can escape, and reaching internally 



to the axis of the barrel, while the extremities are a few 



inches above its surface*. 



*This must make an unnecessary addition to the weight of the 

 machine, and cost of materials, at the same time that they must 

 be liable to injury. They would admit the outer air equally well, 

 if the external aperture were level ■ with the surface of the 

 barrel. T. 



IX. An 



