dyeing vegetable fabrics mordanted with alumina. If, however, strong ammonia be employed to dissolve the purpurine, considerable heat is produced-a rise of temperature of as much as 20° C. taking place if the bulb of a thermometer be immersed in finely divided purpurine and strong ammonia poured on it.

The purpurine employed in these experiments was prepared by Kopp's process, and I am indebted for it to my friend Professor Crace Calvert.

The solution of the new substance, purpureine, is filtered to separate dust, &c., as well as a black substance insoluble in dilute ammonia; it is then added to a considerable quantity of dilute sulphuric acid, boiled for a short time, and allowed to cool. When cold, the impure purpureine is collected on a filter, well washed, and dissolved in a small quantity of hot alcohol. The spirituous solution is again filtered into a quantity of very dilute boiling sulphuric acid, about 1 part acid to from 50 to 100 of water; when cold, the precipitate is collected and again well washed. A crystallization out of boiling very dilute acid now renders it quite pure. This somewhat long and tedious process is necessary to free it from an uncrystallizable black substance, a part of which is separated when the crude purpureine is dissolved in alcohol, and a part is left behind at the last crystallization.

This compound being in its mode of formation and physical properties very analogous to orceine, I have called it purpureine. When crystallized by the spontaneous evaporation of its alcoholic solution, or from boiling dilute sulphuric acid under peculiar conditions of aggregation, it presents a fine iridescent green colour by reflected light; whilst under the microscope it appears as fine long needles of a very deep crimson colour. As obtained by the process above described, it has, however, but little of the iridescent appearance, being of a brownish-red colour with a faint tinge of green. It is almost insoluble in cold dilute acids, and is in great part precipitated from its aqueous solution by common salt, thus greatly resembling orceine. It is almost insoluble in bisulphide of carbon, very slightly so both in ether and in cold water, much more so in hot, and very soluble in spirit both hot and cold and in water rendered slightly alkaline. It is readily soluble in cold concentrated sulphuric acid, and is precipitated unaltered by water; on heating, however, it is destroyed.

Its aqueous solution gives a deep-red precipitate with chloride of zinc; with chloride of mercury a purple gelatinous precipitate; and with nitrate of silver a precipitate of a very dark brown colour slightly soluble in ammonia. I have been favoured with the following optical examination by Professor Stokes:

:

"Its solutions show bands of absorption just like purpurine in character, but in some cases considerably different in position. The etherial and acidulated (acetic acid) alcoholic solutions show this strongly. The tint is so different in purpurine and its derivative, that the intimate connexion revealed by the prism would be lost by the eye. A drawing of the spectrum for purpurine would serve for its derivative (purpureine), if the bands were simply pushed a good deal nearer the red end."

I. 3435 grm. pupureine gave ·8230 grm. carbonic acid and ⚫1240 grm. of water.

II. 340 grm. purpureine gave 813 grm. carbonic acid and ⚫123 grm. of

The formula therefore appears to be Cee H2 N2 O20?.

66

Nitropurpureine.

When purpureine is dissolved in a small quantity of moderately strong nitric acid, spec, grav. about 1·35, and heated to 100° C., it gives off red fumes, and on being allowed to cool, a substance separates in magnificent scarlet prisms somewhat like chromate of silver, only of a brighter colour; it is quite insoluble in water, ether, and bisulphide of carbon, and very slightly soluble in spirit, but soluble in hot moderately strong nitric acid, from which it separates on standing for a considerable time. If boiled with strong nitric acid, it is slowly decomposed. When heated, it deflagrates: from this circumstance, and considering its mode of formation, it is evidently a nitro-substitution compound; I have therefore called it nitropurpureine. Owing to the small quantity which I have hitherto been able to procure, I have not yet determined the composition of this beautiful body, which is finer in appearance than any of the derivatives from madder I have as yet

met with.

Action of Ammonia on Alizarine.

The alizarine which was employed for the subjoined experiments was obtained by extracting Professor E. Kopp's so-called green alizarine* with bisulphide of carbon. It yields only about 15 per cent. of orange-red alizarine. This was crystallized three times out of spirit, from which it usually separates as a deep-orange-coloured crystalline powder. Unfortunately this alizarine still contains a quantity of purpurine, from which it is impossible to purify it either by crystallization or sublimation. Accordingly, when treated with ammonia by the method already described for purpurine, while it yields a substance analogous to purpureine, the product is impure, being contaminated with purpureine, This mixture has been examined by my friend Professor Stokes, who finds that it contains purpureine, derived from the purpurine present as an impurity in the alizarine employed, and another substance very like alizarine in its optical properties, probably a new substance (alizareine), bearing the same relation to alizarine that

* I am also indebted to Professor Calvert for the "green alizarine."

- purpureine does to purpurine*. The following is an extract from a letter I received from Professor Stokes :

"It would be very unlikely à priori that such a simple process as that of Kopp should effect a perfect separation of two such similar bodies as alizarine and purpurine; and as I find his purpurine is free from alizarine, it would be almost certain à priori that his 'green alizarine' would contain purpurine, and the two would be dissolved by bisulphide of carbon, and might very well afterwards be associated by being deposited in intermingled crystals, if not actually crystallizing together."

Action of Ammonia on Munjistine.

This reaction with munjistine was only tried on a very small scale, but the results were by no means satisfactory. The munjistine was completely destroyed, the greater part being changed into a brown humus-like substance, insoluble in ammonia,—the remainder forming a colouring-substance, analogous to purpureine, but not crystalline. It dyed unmordanted silk a brownish-orange colour.

The combined action of ammonia and oxygen, therefore, on the three colouring-substances alizarine, purpurine, and munjistine, is to change them from adjective to substantive dye-stuffs. I think it not improbable that if this archilizing process were applied to various other colouring matters, they would be found capable of undergoing similar transformations.

Action of Bromine on Alizarine.

A boiling saturated solution of alizarine in alcohol is mixed with about six or eight parts of distilled water, and to this when cold about one or one and a half parts of bromine water are added, when a bright yellow amorphous precipitate is produced. After standing twelve or sixteen hours, the solution is filtered; and if the clear filtrate be now carefully heated so as to expel the spirit, a substance of a deep orange-colour is deposited, consisting of very fine needles, which are contaminated with a small quantity of resin if a great excess of bromine has been employed. These needles are soluble in spirit and ether, insoluble in water, and soluble in bisulphide of carbon, from which they crystallize by spontaneous evaporation, in dark-brown nodules. With soda they give the same purple colour as alizarine. They dye cloth mordanted with alumina a dingy brownish red, very different from the colour produced by ordinary crystallized alizarine. The following optical examination is from a letter of Professor Stokes :

"Bromine Derivative of Alizarine."

"I can hardly distinguish this substance from alizarine. The solutions * Since this paper was communicated to the Royal Society, I find by a notice in Kopp and Wills's Jahresbericht' for 1862, p. 496, that a similar experiment upon alizarine had been made by Schützenberger and A. Paraf. The product of one preparation which they obtained, and to which they have given the name of alizarinamid, yielded a formula C40 H15 NO12, and another preparation gave the formula Cso H2, N2 O24, both being, when dry, nearly black amorphous substances. It appears, therefore, from the results of MM. Schützenberger and Paraf's experiments, that these gentlemen were not more successful in obtaining a pure product from the action of ammonia on alizarine than I have been.

33

in alcohol containing potassa show three bands of absorption just alike in appearance. By measurement it seemed probable that the bromine substance gave the bands a little nearer to the red end; but the difference, if real, was very minute. The fluorescent light of the ethereal solution was, I think, a trifle yellower in the bromine substance, that of alizarine being more orange."

The following are the results of the ultimate analysis of the brominated alzarine dried at 100° C. :

207 grm. bromide of silver.
389 grm. bromide of silver.
221 grm. bromide of silver.
300 grm. bromide of silver.

I. 375 grm. of substance gave II. 703 grm. of substance gave III. 401 grm. of substance gave IV. 543 grm. of substance gave V. 3575 grm. of substance gave '695 grm. of carbonic acid and 0760 grm. of water.

VI. 454 grm. of substance gave 8790 grm, of carbonic acid and ⚫0965 grm. of water.

III.

IV.

V.

VI. 53.03 52.81

....

....

From this somewhat anomalous formula,

Cao H, Br, Os=C, H, O, 2(C, H, BrO,),

60

18

20

I was for some time inclined to think that it might be a mixture of brominated alizarine with free alizarine; but as all the six samples analyzed were prepared at different times, it is highly improbable that such uniform analytical results could be obtained if they were from a mere admixture of substances. The existence of a brominated compound is also confirmed by its dyeing properties, which differ so remarkably from those of alizarine.

Action of Bromine on Purpurine.

When pure purpurine is dissolved in spirit mixed with a considerable quantity of water, and an aqueous solution of bromine added, as in the case of alizarine, a yellow amorphous precipitate is produced. The solution separated from this by filtration, when heated to expel the spirit, gives no precipitate whilst hot; but on cooling, a very small quantity of a brown resinous powder is deposited. From this it is evident that the presence of a small quantity of purpurine in alizarine will not interfere with the production of pure brominated alizarine, if the precaution be taken to collect it from the solution whilst it is still hot.

I think it right to state that the experiments and analyses detailed in the preceding paper have been performed by my assistant, Mr. Charles Edward Groves. I cannot conclude this paper without again acknowledging the essential services I have received from Professor Stokes, who kindly bmitted the different products obtained by me to optical examination.

March 3, 1864.

Major-General SABINE, President, in the Chair.

In accordance with the Statutes, the names of the Candidates for election into the Society were read, as follows :

Sir John Charles Dalrymple Hay, Charles Wye Williams, Esq.

The following communication was read :—

"On the Spectra of Ignited Gases and Vapours, with especial regard to the different Spectra of the same elementary gaseous substance." By Dr. JULIUS PLÜCKER, of Bonn, For. Memb. R.S., and Dr. S. W. HITTORF, of Munster. Received February 23, 1864.

(Abstract.)

In order to obtain the spectra of the elementary bodies, we may employ either flame or the electric current. The former is the more easily managed, but its temperature is for the most part too low to volatilize the body to be