i^ 



COLOURS OF HEATED METALS. 



Caloric has not 

 altered the di- 

 nien-ions of 

 the panicles, 



but separated 

 them progres- 

 sively. 



Similar effects 

 from altering 

 the arraiijre- 

 ment of the 

 particles oi bj- 

 dies. 



Proof of this. 



These effects 

 shown in a 

 striking man- 

 ner. 



bits the same kind of colours, according to the circumstances 

 of its cooling, even ou its lower surface not exposed to the 

 air. 



With regard to the manner in which caloric acts on the 

 metal in these instances, 1 will not say, that it has altered 

 the magnitude of the particles; for how can we conce.ve, 

 that a substance can vary tl^e disposition of 4;he constituent 

 elements of its molecules without changing its nature? But 

 I can more readily conceive, that there has been a progressive 

 separation of the particles, increasing from the part scarcely 

 heated to that in immediate contact with the flame. This 

 separation, from the principles I have laid down, must in fact 

 have been sufficient to produce these rings. 



Besides, we daily see many examples of this sort of co- 

 lours, where the arrangement of the particles appears to be 

 the sole determining cause. Such are the spots formed on 

 knife blades by the acid on fruit; those on silver by sul- 

 phurous vapoiirs, or the continued contact of certain subr 

 stances; and the prismatic colours of pellicles forpied on the 

 surface of liquids coritaining some matter at first dissolved, 

 and afterward precipitated slow^ly by the gradual evaporation 

 of some volatile principle, seen in manuiactories and labo- 

 ratories. The waters of dunghills are sometimes covered 

 with similar colours. 



Now all these effects, whatever be the nature of the pri- 

 mitive matter, or of that secondarily formed, depends only 

 em the arrangement of the parts. Nothing is more easy than 

 to ascertain this. Scratch the surfaces, break the pellicles, 

 and all this tnultitude of colours will be annihilated, the frag- 

 ments of each leaving only particles uniformly possessing 

 the common properties of their kind. 



• The following among others is a very convenient mode of 

 observing these effects. Take a small quantity of Schetle's 

 green, dissolve it in an acid, and, after having largely diluted 

 tiie solution with' water, precipitate by an alkah, and add 

 ammonia merely to rediscolve the precipitate. Let the whole 

 stand in a ve sel not closed, and in a few days the surface 

 w;U be covered with a' very evident coloured pellicie, in 

 yi^hich periodical recurrences of rings wdl be distinguished, 

 if it have remained undisturbed. This pellicle may be taken 



up 



