152 M. Berthier'^s Description of Nontronite. 



Muriatic acid attacks it very easily ; the solution does jiot 

 contain the smallest trace of manganese, nor protoxide of iron, 

 nor alkali; there were found only peroxide of iron, alumina, 

 and magnesia. The insoluble part is gelatinous, and is com- 

 posed of silex soluble in the liquid alkaries, and sometimes 

 mixed with a small quantity of argil, when the mineral has 

 not been picked with great care. 



Nontronite melts readily with the third of its weight of 

 marble. 



The analysis gives 



SiHca, - 44.0 containing 22.9 oxygen. 



Peroxide of ii'on, 29-0 8.9 



Alumina, Z.Q 1.7 



Magnesia, 2.1 0.8 



Water, 18.7 1.6 



Clay, - 1.2 



98.6 



From the quantities of oxygen in each of its elements, Non- 

 tronite is a bisilicate, with a base of peroxide of iron, alumina, 

 and magnesia, and may be represented by the formula, 



and containing besides a certain proportion of water in combi- 

 nation ; but it is difficult to determine this proportion accu- 

 rately, on account of the facility with which the mineral ab- 

 sorbs, or loses a certain proportion of water according to the 

 smallest changes of temperature. We have seen indeed, that 

 when it is kept long immersed in this fluid, it absorbs one- 

 tenth of its weight of it, and contains from 28 to 30 per cent. ; 

 when it is left for several days in the air of a room, it con- 

 tains only from 21 to 22 per cent. ; and when it has been ex- 

 posed in a stove heated to 80° Cent., it only loses by calcina- 

 tion 18.7 per cent. If we admit this last quantity to be the 

 minimum, it will follow that the water of combination con- 

 tained in the Nontronite contains IJ times as much oxygen as 

 the three bases together. 



