1825.] On the Red Colour of Ciystallized Felspar. 433 



a red colour ; which colour, with the increase of heat, was 

 found entirely to disappear, and the substance assumed at last 

 as pure a white, as it possessed after the first fusion. A lump 

 of the original mass was found to undergo no change of colour 

 at the same heat, and I have uniformly found, after several 

 trials, that the depth of the colour depends on the fineness of 

 the grinding. A portion was mixed with nitre, which almost 

 entirely destroyed the colour, a proof that it cannot be attri- 

 buted to manganese, which might perhaps be suspected, as nitre 

 always deepens the colour of manganese in a remarkable 

 manner. 



I observe some doubts were expressed in your January num- 

 ber as to the nature of some specimens from Caernarvon : for 

 my own part, as soon as I found that parts of the rock naturally 

 of a red colour became white in strong fire, I had no doubt those 

 parts consisted of felspar. 



No. 1 is the result of the first fusion, the materials having 

 been imperfectly mixed, it is porous, and not uniform, but of a 

 good white. 



No. 2 is the same substance finely ground in a porcelain dish. 



No. 3 is a portion of No. 2, which has been exposed to a low 

 red heat, nearly that of melting silver.* 



No. 4 is another portion of No. 2, which has been exposed to 

 a heat somewhat stronger.-f- 



No. 5 is another portion of No. 2, which has been exposed to 

 a moderate white heat.^ 



No. 6 is another portion mixed with one-fifth nitre, and 

 exposed to the same heat as No. 3.§ C. C. C. 



*^* The phaenomena related in our correspondent's paper are 

 probably merely optical, owing to the different action of the 

 substances on light from their different states of aggregation, 

 according to the degrees of heat to which they have been 

 exposed, — Fdit. 



• This specimen has a peach blossom colour. 



+ Pale bluish lilac colour. 



X Slightly greenish white enamel. 



§ Similar tint to No. 4, but lighter. 



New Series, vol. i\, 2 r 



