ON COLOURING MATTERS. 
139 
Alizarin has the following properties:—When heated on platinum foil it 
melts and bums with a bright flame. When heated in a glass tube closed at 
one end it melts and gives yellow fumes, wliieii condense on the colder parts 
of the gloss, forming an oil, which soon congeals to n mass of orungc-coJoured 
crystals po^^st8sing a considerable lustre, which .arc unchanged alizarin. A 
carbonaceous residue is usually left in this case, But I have uu doubt that by 
carefully heating it might be entirely volatilized. Allzarii) is slightly soluble 
in boiling water. The solution has a yellow colour, but so small is the quan* 
tity dissolved, that the alkali or earth usually coiiiaitied in filtering paper is 
enfficient to render the solution pink, on helog fllterud to separate it from tho 
excess of alizarin. Hence no doubt arises tiie statement found in books, that 
nliuriD dissolves in water with a pink colour. The boiling solution deposits 
it on cooling In yellow crystalline flocks. It is solidile in boiling alcohol. 
The solutioD has a deep yellow colour and deposits nothuig on cooling, but 
on evaporation the alizarin is left in long needle*shaped or prismatic orange- 
coloor^ crystals possessing a considerable lustre, lire colour of the ciystaU 
much resembles that of bichromate of potash. Concentrated sulphuric 
arid dissolves alizarin in tlie cold with n blood-rod colour. It is precipitated 
from this solution by water in flocks of a dull orango colour. Dilute nitric 
arid decomposes it on boiling with an evolution of nitrous acid. If it is still 
Jrixed with fat, then the fat remains beliiuil after the alizuriu has been de- 
cainposed and dissolved by tlie nitric acid. It Is not affected by muriatic or 
®<!ct3c acid. On passing chlorine into water in wlriob alizarin is suspended, 
the colour of tlie latter is changed to yellow, but it is seenringly not destroyed. 
It is decomposed by bichromate of potash and sulphuric acid. A boiling 
solution of pcrcliloride or pcrultrato of iron dccompoHcs it, with a copious evo¬ 
lution of gag, a pungent ami'll rescmblhig that of aldehyde being at the same 
tMe given off. ’fhe product of tins decomposition 1 shall tlescrilic presently, 
khloride of gold is not reduced by it on boiling, but on the addition of cau¬ 
stic poia-jh metallic gold is deposited in shining scales. It is soluble in caustic 
^d carbonated alkalies with a splendid purple colour, and is repivcipitated 
ty acids in flocks of a dull orange colour. Tho solution in ammonia gives 
^dn the chlorides of barium mid calcium prccipibUi.-w of a splendid purple 
^'our, witii sugar of lead a light purple predpitnte. The compound with 
wanmia, produced by introducing liydratc of alumina into an alcoboHc solu- 
T is not decomposed by a concentrated solution of caustic pot- 
^h. Tlie alcoholic solution gives with acetate of iron a dark pur[)l<: jircci- 
piiatp, with acetate of copper a light purple precipitate, with protochloride 
°except on the addition of ammonia, when a light red 
pfei^itate is produced. If alizarin and a piece of mordanted cloth be iutro- 
into boiling water and the boiling be cuniinued for some time, the cloth 
slowly dyed and the mordants assume the tints peculiar to tlie so- 
“Judder colours. The alizarin slowly disappears in the same measure 
soft ' dyed, even thougJi lesw water Itad been takeu than was 
cirot to dhisolvn the whole quantity. It is evident therefore that in the 
ot dyeing, the alizarui, which is dissolved in tliu first instance by the 
ujg Water, is taken up l»y the mordants of ihe cloth, tiiat then a fresh 
is dissolved by the water, which is again absorbed, and so on, until 
tlie alizarin has combined with the cloth, or until the mordants! can take 
P no more. Hence the slowness w ith which madder dyeing is effected. No 
duA?* I flank, Uiat alizarin plays a great part in the pro- 
uon of madder colour*. That it does not produce the whole effect in 
Th^ k ^ show afterwards, 
ne method of obtaining alizarin in a state of purity I have discovered so 
