1819.] On Native Hydrous Aluminate of Lead. 31 



Article IV. 



On Native Hydrous Aluminate of head, or Plomb Gomme. 

 By James Sinithson, Esq. 



Paris, May 22, 1819. 



I see in the Annals of Philosophy for this month, which I 

 have very lately received, an analysis by M. Berzelius of the 

 mineral which was formerly known here under the name of 

 " plomb gomme." 



The first discovery of the composition of this singular substance 

 belongs, however, to my illustrious and unfortunate friend, and 

 indeed distant relative, the late Smithson Tennant. He ascer- 

 tained when last at Paris, on pieces furnished him by M. Gillet 

 de Laumont, that it was a combination of oxide of lead, alumina, 

 and water. 



At that time I received a small specimen of this rare ore from 

 M. de Laumont, accompanied with a label, of which the follow- 

 ing is a copy : 



" Hydrate d'alumine et de plomb reconnu par Mr. Tennant, 

 du Huelgoat, pres Poullaouen, en Bretagne (Finistere) qui paroit 

 etre la meme substance decrite par Rome de ITsle, torn. iii. de la 

 Cristallographie, p. 399, comme plomb rouge en stalactite. 



" J'en ai dit quelques mots en Mai, 1788, dans le Journal de 

 Physique, p. 385, F. 16." 



This ore is of a yellow colour ; it otherwise bears so great a 

 resemblance to the siliceous substance found near Frankfort on 

 the Mein, called Mullen glass, that it might be mistaken for it. , 



Suddenly heated, it decrepitated violently ; but heated slowly, 

 it became white and opaque. The utmost fire did not appear to 

 fuse it, or produce any further alteration in it. 



It dissolved readily in borax into a colourless transparent glass, 

 but no reduction of lead took place. Not having any carbonate 

 ( f soda at hand, I added a particle of nitre, whose deflagration 

 producing potash, lead was revived. 



A bit, which had been made white by ignition, being wetted 

 with nitrate of cobalt and again ignited, became blue. 



Heated in a glass tube over a candle, it decrepitated, became 

 opaque and white, and water sublimed. 



Mr. Tennant mentioned to me a sort of explosion occasioned 

 by the sudden expulsion of the water, and characteristic of this 

 ore, which took place when it was heated at the blow-pipe. With 

 the very minute particles I have tried, no effect of this sort was 

 perceived. 



The above characters will prove sufficient, I apprehend, to 

 make this substance known when met with. 



