Royal Society. ^7 



to conclude that alizarine and verantine are capable of forming a 

 double compound with alumina soluble in boiling water, and that a 

 mixture of the two in the proportion in which they exist in this 

 compound constitutes what has been called purpurine. 



Although the difficulty of obtaining pure verantine in sufficient 

 quantity for the purposes of analysis prevented the author from de- 

 termining its composition with the requisite accuracy, he obtained 

 approximations sufficiently near to remove almost all doubts on the 

 question. The formula deduced from four experiments is C* H^ O^ ; 

 so that it appears that verantine differs from alizarine by containing 

 1 equiv. more of oxygen. 



3. Rubiretine is identical with the substance which the author 

 formerly called Alpha-resin of madder. He endeavoured in vain to 

 determine the atomic weight of this substance ; but states that there 

 is only one formula which is in accordance with his analyses, and at 

 the same time satisfactorily explains its formation. This formula is 

 C* H^ O^ ; so that 2 equivs. of verantine and 2 equivs. of rubiretine 

 with 12 equivs. of water give 1 equiv. of rubian. 



4. Rubianine greatly resembles rubiacine in its appearance and 

 many of its properties. It may however easily be distinguished by 

 several characteristics, and above all by its composition. It is ob- 

 tained from a solution in boiling alcohol in the form of bright lemon- 

 yellow silky needles, which when dry form an interwoven mass. It 

 is less soluble in alcohol, but more so in boiling water, than any of 

 the preceding substances. On the solution in boiling water cooling, 

 it crystallizes out again in yellow silky needles. Its colour is lighter 

 than that of rubiacine. When heated on platinum foil, it melts to a 

 brown liquid ; then burns, leaving a carbonaceous residue, which on 

 further heating disappears entirely. It is soluble in concentrated 

 sulphuric acid, with a yellow colour; the solution on boiling be- 

 comes black, and gives off sulphurous acid. It is not affected either 

 by dilute or concentrated nitric acid even on boiling; it merely dis- 

 solves in them, and, on the acid cooling, crystallizes out again as 

 from boiling water. 



There are three forniulge, all of which give for 100 parts of this 

 substance numbers not widely differing from those deduced from the 

 analyses, viz. C^'H^O's, C^aH'sO'S C^* H'^^ 0'^°, but the last is 

 that with which they best agree. 



5. The sugar is always obtained in the form of a transparent 

 yellow syrup, vhich neither crystallizes, however long its solution 

 may be left to stand, nor becomes dry unless heated to 100° C. 

 There are two formulae, C'^ H'*0'^ and C'« H'^ O'S both of which 

 agree with the analyses of this substance, and explain its formation. 

 'J"he author states the views to which each of these formulae gives 

 rise, and the reasons for adopting the latter. 



Although five substances are produced by the action of acids on 

 rubian, tin- author does not consider that these substances are all 

 formed together, or in other words, that one atom of rubian, by its 

 decomposition, gives rise to all five at the same time; but that, from 

 the composition of these substances as compared with that of rubian, 

 it follows, that the decomposition aft'ects three separate atoms of ru- 



