ON COLOURING MATTERS. 61. 
and filtering boiling hot, the liquid deposited on cooling orange-coloured 
flocks, which were impure alizarin, for they dyed mordanted cloth, and after 
being dried and heated in a tube, they gave a crystalline sublimate. The 
3 iquid gave on evaporation pectic acid. ‘That part of the precipitate which 
_was left undissolved by boiling water, was treated with a boiling solution of 
nitrate of iron. The filtered liquid gave, on the addition of muriatic acid, a 
ight yellow precipitate, which was probably rubiacic acid from the rubiacin 
of the precipitate. The greater part was insoluble in nitrate of iron. By 
treating the insoluble residue with boiling muriatic acid, filtering, washing 
with mater, and treating with boiling alcohol, an abundance of barns -resin was 
_ procured. 
I infer from these experiments that the substances extracted Bian madder 
by caustic potash, after exhaustion with boiling water and treating with acid, 
| previously existed in the root in combination with lime and magnesia ; that 
_ these substances are not different from those extracted by hoiling water, viz. 
' alizarin, rubiacin, resins and pectic acid ; that the compounds of yHisse bodies 
with lime and magnesia are insoluble in water, and, with the exception of 
pectate of lime, insoluble i in caustic alkalies ; and that therefore, in order to 
extract them by means of water or an alkali, it is first necessary to remove 
the lime and magnesia with which they are combined by means of an acid. 
I shall now proceed to give some further details concerning the properties 
and composition of the substances extracted from madder. 
Alizarin.—Concerning the properties of alizarin I have nothing to add to 
| what I stated in my last report, except that when crystallized from alcohol it 
_ contains several atoms of water of crystallization, which it loses when heated 
to 212° F. The crystals after being heated to this point have not lost their 
shape, but have become opake and of a much redder colour, resembling 
that of native chromate of lead. On placing them in a tube immersed in a 
} sulphuric- acid bath, and heating the bath, no further change takes place until 
about 420° F., when a sublimate of orange- -coloured crystals begins to appear 
on the cold part of the tube. 
On subjecting alizarin to elementary analysis I obtained the following 
results :— 
I. 0°3205 grm. of crystallized alizarin dried in the air gave, on being burnt 
es chromate of lead, 0°6695 carbonic acid and 0°1210 water. 
If. 0°3985 grm. of the same gave 0°8320 carbonic acid and 0°1850 water. 
III. 0°3140 grm. gave 0°6565 carbonic acid and 0°1670 water. 
_ These numbers correspond in 100 parts to— 
LP ee | AL LLL LO EGOS COTTE, 
I. Il. Ill. 
Carbon ...eeeeeeeee 56°97 56°94 57°02 
4 Hydrogen ......00-. 4°19 518 5°87 
a Oxygen .eseeseeeeee 38°84 37:93 37-11 
100-00 100°00 100°00 
a “The great discrepancy i in the amounts of hydrogen in the preceding ana- 
lyses arises from the circumstance that alizarin loses its water of crystalli- 
tion with such extreme facility. No.1. was mixed with warm chromate of 
ad in a warm mortar; No. II. was mixed with warm chromate of lead in a 
cold mortar; and No. TIL. with cold chromate of lead in a cold mortar. In 
the case of N o. I. therefore we see that the heat of the chromate of lead and 
e mortar combined was sufficient to drive away more water than what cor- 
sponds to 14 per cent. of hydrogen, though this heat was not greater than 
hat might be borne by the hand. In order to determine the amount of 
LD POT TS OE PD ae 
