396 Scientific Intelligenee. [Nov. 



changed. The substance produced is hard and brittle, it splits on the 

 bail, and presents an appearance like some hard varieties of earthy 

 haematite ; its colour is brown, becoming, when heated, red ; it fuses, 

 on platinum Foil, into a yellow flaky substance like litharge. Powdered 

 and boiled in water, no muriatic acid or lead was found in solution. It 

 dissolved in nitric acid without leaving any residuum, and the solution 

 gave very faint indications only of muriatic acid. It is a protoxide of 

 lead, perhaps formed, in someway, by the galvanic action of the iron 

 shell and the leaden ball, assisted, probably, by the sea water. It 

 would be very interesting to know the state of the shells in which a 

 change like this has taken place to any extent ; it might have been 

 expected, that as long as any iron remained, the lead would have been 

 preserved in the metallic state." — (Institution Journal, for Oct. 1823.) 



V. Action of Gunpotoder on Lead. 



Mr. Faraday savs, that *< Mr. Marsh gave me also some balls from 

 cartridges about fifteen years old, and which had probably been in a 

 damp magazine. They were covered wiih white warty excrescences 

 rising much above the surface of the bullet, and which, when removed, 

 were found to have stood in small pits formed beneath them. These 

 excrescences consist of carbonate of lead, and readily dissolve with 

 effervescence in weak nitric acid, leaving the bullet in the corroded 

 state which their formation has produced. It is evident there must 

 have been a mutual action among the elements of the gunpowder itself, 

 at the same time that it acted on the lead ; and it would have been 

 interesting, had the opportunity occurred, to have examined what 

 changes the powder had suffered." — (Ibid.) 



VI. Purple Tint of Plate Glass affected hy Light, 



•* It is well known,'* says Mr. Faraday, " that certain pieces of plate 

 glass acquire, by degrees, a purple tinge, and ultimately becoaie of a 

 comparatively deep colour. The change is known to be gradual, but 

 yet so rapid as easily to be observed in the course of two or three 

 years. Much of the plate glass which was put a few years back into 

 some of the houses in Bridge-street, Blackfriars, though at first colour- 

 less, has now acquired a violet or purple colour. Wishing to ascertain 

 whether the sun's rays had any influence in producing this change, the 

 following experiment was made : — Three pieces of glass were selected, 

 which were judged capable of exhibiting this change ; one of them was 

 of a slight violet tint, the other two purple or pinkiyh, but the tint 

 scarcely perceptible, except by looking at the edges. They were 

 each broken into two pieces, three of the pieces were then wrapped up 

 in paper, and set aside in a dark place, and the corresponding pieces 

 were exposed to air and sunshine. This was done in January last, and 

 the middle of this month (September), they were examined. The 

 pieces that were put away from light seemed to have undergone no 

 change ; those that were exposed to the sunbeams had increased in 

 colour considerably ; the two paler ones the most, and that to such a 

 degree, that it would hardly have been supposed they had once formed 

 part of the same pieces of glass as those which had been set aside. 

 Thus it appears that the sun's rays can exert chemical powers even on 

 such a compact body and permauent compound as gla»s."— (Ibid.) 



