1864.] Dr. Wolf on the Magnetic Variations at Greenwich. 87 



Pui'pureine. 



When purpurine is dissolved in dilute ammonia, and exposed to the air 

 for about a month in a warm place, ammonia and water being added from 

 time to time as they evaporate, the purpurine disappears, whilst a new 

 colouring matter is formed, which dyes unm.ordanted silk and wool of a 

 fine rose-colour, but is incapable of dyeing vegetable fabrics mordanted with 

 alumina. 



This new substance, which, from its mode of formation and physical pro- 

 perties, is so analogous to orceine, I have called purpureine. When pure, 

 it forms fine long needles of a deep crimson colour, insoluble in dilute acids, 

 slightly soluble in pure water, and very soluble in alcohol and in water 

 rendered slightly alkaline. Professor Stokes has examined purpureine 

 optically, and finds the spectrum the same in character as that of purpurine, 

 but different in position, the bands of absorption being severally nearer to 

 the red end. 



From the analyses, purpureine seems to yield the formula Cgg Hg^N^O^Q. 

 Nitropurpurine, 



When purpurine is dissolved in a small quantity of nitric acid, spec, 

 grav. about "135, and heated to 100° C, it gives ofP red fumes, and on 

 being allowed to cool, a substance separates in fine scarlet prisms, some- 

 what like chroraate of silver, only of a brighter colour. It is quite inso- 

 luble in water, but slightly soluble in spirit ; it is, however, soluble in strong 

 nitric acid. When heated, it deflagrates. From this circumstance, and 

 considering its mode of formation, it is evidently a nitro-substitution com- 

 pound. I have therefore called it nitropurpurine. 



When alizarine and munjistine are subjected, in the manner above de- 

 scribed for purpurine, to the joint action of ammonia and oxygen, substan- 

 tive colours are produced, neither of which are crystalline. 



Action of Bromine on Alizarine. 

 When alcoholic solutions of alizarine are mixed with water, and aqueous 

 solution of bromine added, a yellow precipitate is produced ; the solution 

 filtered from this, after expelling the spirit by heat, deposits a deep orange- 

 coloured crystalline compound, which, from the analyses of six specimens 

 prepared at different times, I find has the composition 



Ceo Br, 0,3= H3 O3, 2(C,„ H, BrOJ. 

 Purpurine, when treated with bromine in a similar manner, does not yield a 

 corresponding compound. 



II. " On the Magnetic Variations observed at Greenwich.^^ By Pro- 

 fessor Wolf of Zurich. Communicated by C B. Airy, F.R.S.^, 

 Astronomer Royal. Received December 21, 1863. 



(Translation.) 



In April 1863 Professor Airy kindly communicated to me the Mean 



