produced ly Heat in coloured Bodies. 431 



tion ; but T shall only regard those here, which, being sub- 

 ordinate to the intensity of heat, cease to take place imme- 

 diately when the tcmperatine resumes its primitive slate. 

 I shall divide this n:emoir into two parts: the first will 

 contain a detail of facts, and the second their relations with 

 other phaenomena. 



First Part. ^ 



I outrht to premise, that in the following experiments I 

 have not taken an exact account of the temperature to which 

 the coloured bodies have been exposed. I generally con- 

 tented myself with heating pieces of porcelain upon burning 

 coals, and afterwards throwing coloured bodies upon them: 

 sometimes however I exposed them upon an earthen plate 

 at the heat of the sand-bath, but never lower than 100°, or 

 higher than 400°. Lest I should inaccurately define the 

 various changes of colour produced by heat, I requested 

 M. Merimee, who is well versed in the colour business, to 

 be present at my experiments, and to write down the re- 

 sults with his own hand. I cannot do better, therefore, 

 than faithfully republish the notes which he took upon that 

 occasion. 



Experiment 1. — Chinese Vermilion. 



Its colour is not a pure red : it contains yellow. On ex- 

 posing it to the heat of the sand-bath it became deeper, and 

 assumed the carmine shade. 



Experiment 2. — Oxide of Mercury obtained ly the Calcina- 

 iion of the Nitrate of' Mercury. 

 Its colour is orange. At the temperature of 100° it as- 

 sumed a deepish red, and approached the colour of com- 

 mon cinnabar: at a stronger heat it became of a fine cin- 

 nabar red, and at a still stronger heat about 300° it passed 

 to the violet colour, first assuming a blue colour. The 

 colour of this oxide being orange renders it capable of 

 passing to a brilliant red, but not to a fine violet*. 



Experiment 3. — Red Lead. 

 It presents nearly the same phjcnomena with the oxide 

 of mercury ; but, as its orange colour is finer, heat makes 

 it assume a more brilliant red. The violet colour which is 

 developed in it afteiwards is not finer than that of the oxide 

 of mercury. 



• When we pound this oxide of mercury, it tiikcs an olive yellow sliade 

 deeper than its ptiniitivc colour, and wliicli is dcvcliipcd the lietlcr, the 

 jnore llie oiide is> poiiiidtd. This new colour gets deeper when heated, 

 and become* of a ciiuiamou colour. 



Experi- 



