WRITINGS OF JAMES SMITHSON. 67 



ON NATIVE HYDROUS ALUMINATE OF LEAD, 

 OR PLOMB GOMME. 



From Thomson's Annals of Philosophy, Vol. XIV, 1819, p. 31. 



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 unfortu- 

 nate friend, and indeed distant relative, the late Smithson 

 Tennant. He ascertained when last at Paris, on pieces fur- 

 nished him by M. Gillet de Laumont, that it was a combi- 

 nation 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 following is a copy : 



" Hydrate d'alumine et de plomb reconnu par Mr. Ten- 

 nant, du Huelgoat, pres Poullaouen, en Bretange (Finisterre) 

 qui paroit etre la meme substance decrite par Rome de PIsle, 

 torn. iii. de la Cristallographie, p. 399, comme plomb rouge 

 en stalactite. 



" J'en ai dit quelques mots en Mai, 1786, 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 Frank- 

 fort on the Mein, called Mullen glass, that it might be mis- 

 taken 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 



