the Analyses of M. Klaproth. 339 



trown earthy powder. It is composed of a browTi carbo- 

 uaceous earth, which may easily be known, as it is entirely 

 converted into ashes by exposure to fire. On this account 

 Cronstedt gave it the name of mumia vegetalis, and Wallerius 

 calls it humus umlra. This substance has nothing in com- 

 mon with the real umber earth but the colour. 



On the other hand, umber earth is incombustible, and, 



according to its constituent principles, ought to be classed 



among the ores of iron. It may be considered as a variety 



of bog iron ore. The only analysis made of it before that 



of Klaproth was by M. Santi, who anailysed that of Castel 



del Piaro. The proportions he indicates are as follow : 



Oxide of iron - - - 53 



Alumine - - - 24 



Silex . - - - ly 



Mamesia - - - 4 



100 



But as INI. Santi makes no mention of manganese, which 

 however is one of the essential principles of umber earth, 

 this omission must excite some doubts in regard to the cor- 

 rectness of the proportions which he indicates. The umber 

 earth employed in the following analysis was procured 

 from the island of Cyprus : it resembles externally that 

 known in commerce under the name of fine Turkish umber, 

 and is equally good for painting ; it would therefore be su- 

 perfluous to describe its exterior characters. 



1st. Kept at a red heat for half an hour in a crucible, it 

 lost 14 })er cent, of its weight. But it experienced no other 

 alteration except that its colour had become a darker 

 brown. 



2d. Exposed to a more violent heat, itenters into fiision. 

 M. Klaproth put a fragment weidiing 200 grains into a 

 cliarcoai crucible, which he placed in a porcelain furnace. 

 He took out the crucible quite sate, and containing a button 

 well fused under a thick vitreous scoria of a hvacinth co- 

 lour, and covered v. ith points at the exterior surface. This 

 metallic button was a little tenacious in its fracture under 

 the hannner, and presented a granulated tissue like that ot 

 steel. It weighed 60 grains, and the vitreous scoria 47- 

 The loss consequently amounted to 362 per cent. 



A hundred grains of um.bcr earth well pulverized, mixed 

 with 200 grains of concentrated sulphuric acid evaporated 

 to drvness, were broueht to a red heat in a crucible by 

 mean's of a very strong fire. The red mass appeared ot a 

 brick colour : it was porous, and easy to be pulverized. 

 Y 2 When 



