30 ‘ REPORT—1843. 
at the same time particles are obtained of all the most dissimilar colours, so that 
they represent together a pattern map of all the most dissimilar kinds which are 
obtained of the mineral orthite, from the light red brown to the nearly black. The 
powder becomes light brown, If this oxide be heated to a white heat, it assumes a 
dirty white colour approaching gray green. Oxide of didymium is a weaker basis 
than oxide of lanthanium; it has no alkaline reaction, and appears not to absorb 
water after having been heated. It is, however, tolerably easily dissolved even in 
diluted acids, and the brown oxide with a development of gas. It is insoluble in 
carbonate of ammonia; its salts are amethyst-red, as well as the solutions of the 
salt, which forms no precipitate with hydrosulphuret of ammonia, unless a large 
quantity be added, or the liquid be heated, when the sulphuretted hydrogen is 
developed, and a basic salt precipitated having a slight tint of red. If the oxide be 
dissolved in phosphoric salt by means of the blowpipe, the bead becomes amethyst- 
coloured with great tendency to violet, exactly as with a trace of titanic acid after 
reduction. 
Oxide of didymium heated upon platina foil with carbonate of soda, melts to a 
gray-white mass. With regard to the salts of didymium, I shall briefly describe 
those which are analogous to the before-mentioned salts of lanthanium and cerium, 
and must at the same time mention that the basic salt of didymium which is preci- 
pitated by caustic ammonia, can be washed without passing through the filter. 
The mode in which sulphate of oxide of didymium is obtained, as well as its ap- 
pearance, has been already stated ; this salt is readily soluble in water at the ordi- 
nary temperature of the air, although the crystals are very slowly dissolved. ‘The 
anhydrous salt is at once dissolved, if before the solution it is not suffered to com- 
bine with water of crystallization. Should this occur in such a manner that the an- 
hydrous salt is covered over (dfver gjutes) with a little water, the mass becomes 
heated, and a hard salt crust is formed, which must be reduced to powder before it 
can be quickly dissolved. At the ordinary temperature of the air, one part of an- 
hydrous sulphate of oxide of didymium requires five parts of water for solution. 
This solution begins at 127°4 Fahr. to deposit crystals, the number of which in- 
creases in the same degree as the temperature increases, so that the boiled solution 
contains only one part of anhydrous salt to 50°5 parts of water; at a low red heat 
an inconsiderable quantity of sulphuric acid goes off, but after an hour’s exposure to 
a white heat, the salt loses two-thirds of its acid. With sulphate of potash, sulphate 
of oxide of didymium gives an amethyst-coloured double salt, which is completely 
insoluble in a saturated solution of sulphate of potash. 
Nitrate of oxide of didymium is very soluble in water, crystallizes with difficulty ; 
the solution evaporated to thin syrup, has a beautiful red colour, which seen in a 
certain direction approaches blue. If the salt be evaporated to dryness in a warm 
place, and heated to melting, which cannot be effected without a great portion of 
the nitric acid being decomposed, a red fluid is obtained, which, cooled and solidified, 
does not fall to powder with violence, like the corresponding salt of lanthanium, but 
retains its form. 
I must not omit to mention on this occasion, that amongst the many other bodies 
which in the course of these researches 1 was obliged to examine, yttria also pre- 
sented itself, and I have found that this earth, free from foreign substances, is per= 
fectly colourless, and gives perfectly colcurless salts: that the amethyst colour which 
the salts generally present comes from didymium, I will not, however, maintain. 
Addendum, July 1843.—On Yttria, Terbium and Erbium. 
I published last summer a short notice of yttria, concerning which earth the follow- 
ing facts subsequently discovered merit attention, When I stated on the former 
occasion that pure yttria, as well as the salts of that base with a colourless acid, are 
colourless, my experiments had only gene so far as to show that all the yttria which 
I could procure for examination might with ease be separated into two portions, the 
one a stronger and colourless base, the other a weaker, which, in proportion as it 
was free from yttria, acquired a more intense yellow colour on being submitted to 
heat, and with acids gave salts of a reddish colour. I continued my examination 
