il6 Sir Humphry Davy's experiments and observations 
menting the imperial baths; and it is not impossible that 
Pliny may have alluded to the palace of the Caesars when 
he says “ nunc et purpuris in parietes migrantibus, et India 
conferente fluminum suorum limum, et draconum et ele- 
phantorum saniem, nulla nobilis pictura est.” Lib. xxxv. 
Cap. 32. 
I have seen no colour of the same tint as this ancient lake 
in any of the ancient paintings in fresco. The purplish reds 
in the baths of Titus are mixtures of red ochres and the blues 
of copper. — In the Aldobrandini picture there is a purple in 
the garment of the Pronuba, but of an inferior hue; and this 
purple appears to be a compound mineral colour of the nature 
of these. — It was not destroyed by solution of chlorine ; and 
when a little of it was exposed to muriatic acid, it rendered the 
acid yellow, and the remainder yielded a residual blue powder. 
VII. Of the blacks and browns of the Ancients. 
There is one chamber in the baths of Titus of which the 
ground work is black. I have found several fragments of 
stucco painted black both in the baths of Titus and in the 
vineyard above mentioned, and also in some ruins near the 
Porta del Popolo. — I scraped off some of these colours and 
submitted them to experiments : they were not acted on by 
acids or alkalies, they deflagrated with nitre, and had all the 
properties of pure carbonaceous matter. 
I found no blacks, but three different shades of brown in the 
vase of mixed colours ; one was snuff colour, one deep red 
brown, and the third a dark olive brown. The two first 
proved to be ochres wiiich had been probably partially cal- 
cined ; the third contained oxide of manganese, as well as 
