Intelligence and Miscellaneous Articles. 75 



CHEMICAL EXAMINATION OF WAD. BY DR. TURNER. 



Under the name of Wad, or Black Wad, are comprehended several 

 minerals, which are distinguished by the following characters :— They 

 are soft, light, and porous, more or less earthy in appearance, of a 

 brown colour, soil by contact, and contain manganese. Though 

 they agree in these general points of resemblance, several of them 

 are distinguishable from each other by physical properties, and differ 

 essentially in chemical constitution. 



First species. Wad from Upton Pyne in Devonshire. 



For this Wad I am indebted to the kindness of Mr. Konig of the 

 British Museum. It occurs in a curved tabular mass about half an 

 inch thick, and may be easily separated into thinner lamina?. It is 

 easily broken, is considerably softer than gypsum, and soils when 

 handled. Its colour is brown with a shade of yellow, somewhat like 

 that of bismuth. The lustre of a fresh surface is considerable, and 

 rather metallic. The streak is brown and shining. It consists of 

 small scaly particles, arranged together so as to give to a broken 

 surface a fibrous appearance. It is very porous, and emits numerous 

 air-bells with a hissing noise when put into water. Its specific gravity, 

 after being boiled in water, is 2*314. 



100 parts of the mineral were resolved into 



Red oxide of manganese 79*12 



Oxygen 8*82 



Water I0C6 



Baryta 1 '40 



TochkT 



The essential ingredient of the mineral, inferred from these num- 

 bers, appears to be a hydrated peroxide of manganese, consisting of 

 88 parts or two equivalents of peroxide, and 9 parts or one equivalent 

 of water, — a compound which, to my knowledge, has not been observed 

 in the mineral kingdom. Were such a compound quite pure, the 

 analysis should have given the following proportions : — Red oxide 

 79 - 12, oxygen 10*57, and water 9; — that is, rather less water and 

 rather more oxygen than was actually obtained. 



The hydrated peroxide of manganese may be regarded as the es- 

 sential ingredient of the Devonshire Wad, and, according to my ob- 

 servation, is the most frequent variety of this mineral. I have not 

 met with it in a state of perfect purity. It usually contains small 

 quantities of some other oxide of manganese, together with baryta, 

 oxide of iron, lime, and silica. 



Second species. Wad from Derbyshire. 



This Wad, for which I am indebted to Mr. Konig, is earthy without 

 the slightest crystalline appearance. It acquires a slight lustre by 

 friction, but is otherwise dull. It is very soft and friable, and soils 

 when handled. Its streak and powder are of a reddish-brown colour. 

 It absorbs moisture greedily on being wetted, and when put into 

 water emits numerous globules of air with a hissing noise. Its spe- 

 cific gravity, after its contained air is expelled, is 3*024. It separates 

 readily into parallel layers, the natural joinings being formed by thin 



L 2 strata 



