ON COLOURING MATTERS. 
143 
chloride of tin a dirty yellow precipitate j with percliloride of tin a light 
yellow precipitate; with chloride of gold a yellow precipitate, not changed 
by boiling the fluid. 
I have analysed rubiacin, rubiacic acid, and rubiacate of potash, and have 
obtained results which agree very well with one another. These analyses 
give for rubiacin the fonimla C-,, 11^ 0,0, for rubiacic. acid C,, Us O,;, and 
for rubiacate of potash Cj, 11; 0,^ + KO. It thcrcibre appears that rubiacic 
acid cojitaios seven atoms of oxygen more than rubiacin, aod tlic facility with 
which they may be converted one into the other is easily conceivable. In 
rubiacate of potash two atoms of water existing iu rubiacic acid are replaced 
by oue atom of potash, which is not usually the case vrith potasli salts. 
1 do not, however, consider these foroiul® as completely established, since 
I was obliged, from want of material, to operate on such e-xtromcly small 
quantities. 
This substance is obtained, as I mentioned above, by treating 
the brown precipitate produced by an acid in an extract of madder with 
cold water, after having removed the excess of acid. It has the following 
properties 
In thin layers it is j)orfectly transparent and of a yellow colour. When 
dry it is britUe. It is soluble in water; the .solution lias an extremely bitter 
tabte. A com^ntrated boiling solution forms a jelly on cooling. It is pre¬ 
cipitated from its aijucous solution by all acids, in yellow flocks. It is de¬ 
composed by nitric acid. In the watery solution lime and baryta water 
produce red flocculent precipitates, perehloridu of iron a dark reddish-brown 
wdour, but no precipitate, sugar of lead a brown flocculent precipitate, nitrate 
ofhilrer a docculent precipitate, corrosive sublimate no precipitate, tincture 
of galls and solution <if glue no precipitates. 'I'he solution imparts a slight 
tinge to niordaiited cloth, hat so slight that thU substance cannot be con¬ 
sidered as a colouring matter. The soliUioii deposits nothing during evapo¬ 
ration at all resembling apothem, and if. therefore is not extractive matter. 
It dUsolvca in alcohol with a yellow colour, and in alkalies with a red colour. 
It dissolves in concentrated sul|!huric acid with a red colour; the solution on 
being heated becomes black, and ^ivris olf sulphmous acid. When heated 
platinum foil it ineltn, awells up immensely, and burns, leaving some ash. 
uhen heated in a tube it melts and gives yellow funnw, which condense and 
'»nn a crystalline sublimuto very much ri'sembling rubiacin, so that 1 am 
induced to tliink that there is some relation subsisting between these two 
substances. 
^fchcAcUL —'ritert can hardly be a doubt, I think, that that part of the 
ronn precipitate which is insoluble in alcohol, but soluble in water, is pectic 
c* , as will be seen from its behaviour towards reagents, which Uas follows: 
IS soluble in water; the solution has a light yellow colour, and reddens 
itQi^ pjpg). jg jjjp watery solution acids produce white flocculent 
gelatinous white precipitate, lime and baiy ta water 
WK gelatinous pink precipitates, coimnon salt a Hoecukut precipitate, ni- 
ci n flocculent precipitate, sugar of load a gelatinous reddish pre- 
lim* copper a gelatinous groenUh precipitate, corrosive sub- 
“ ' 110 precipitate. On evaporating the watery solution, the substance 
on the liurfacc of the fluiil in the shape of a pellicle, and i-' left at 
th ** * , ^^riact, which may cosily be detached from the sides of 
e In solutious of caustic and carbonated alkalies it first swells up, 
the fluid it dissolves with a light red colour, forming slimy 
ev€ ** f I?* prceipiiated by acids in flocks. Solutions of salt^ 
Q of alkaline salts, produce precipitates in the alkaline solutions. It is 
