Dr. Schunck on Colouring Matters. 215 



It is probable that the silver salt also contains two equivalents of 

 base to one of acid. 



It follows from the analysis of the lead salt, that the hydrated acid 

 has the following composition : — 



Calculated. 



14 eqs. Carbon 84 57'92 



5 „ Hydrogen 5 3*44 



7 „ Oxygen _56 38-63 



145 100-00 



By the action of nitric acid on alizarine the latter takes up three 

 equivalents of oxygen without losing any hydrogen, for C14 H5 O* 

 + 30 ^ Ci4 H5O7. It appears also that alizaric acid contains one 

 equivalent of hydrogen less, and three equivalents of oxygen more, 

 than benzoic acid. 



Pyro-alizaric Acid. — When alizaric acid is heated it is totally vo- 

 latilized, and forms a sublimate in the shape of long white needles, 

 to which I have given the name of pyro-alizaric acid. By the action 

 of heat alizaric acid loses water, or the elements of water. Pyro- 

 alizaric acid is soluble in boiling water. The solution, however, pro- 

 duces exactly the same reactions as alizaric acid itself, and on eva- 

 poration large rhombic crystals are obtained, which have quite the 

 appearance of the latter acid. It is probable therefore that, by 

 solution in water, pyro-alizaric acid takes up again the elements of 

 water, and is reconverted into alizaric acid. The following results 

 were obtained on analysing this acid: — 



I. 0-4105 grm. dried at 2 12° and burnt with chromate of lead, gave 

 1-0345 carbonic acid and 0-1185 water. 



II. 0*4255 grm. gave 0-9985 carbonic acid and 0-1215 water. 

 From these numbers it may be inferred that the composition is as 



follows : — 



Calculated ^T^' 



Numbers. Z "7? 



28 eqs. Carbon 168 63'87 64-04 63-99 



7 „ Hydrogen 7 2-66 2*98 3-17 



1 1 „ Oxygen 88 33-47 32-98 32-84 



263 100-00 100-00 100*00 



Hence it follows that by the action of heat two equivalents of ali- 

 zaric acid lose three equivalents of water, and give one equivalent 

 of pyro-alizaric acid, since 2(Ci4 H5 O7) — 3HO = Cjs H^ On- 



Rubiacine. — In my last report I described the method of prepa- 

 ration, and the properties of rubiacine and rubiacic acid, and I have 

 nothing further to add to what I there stated. I may mention how- 

 ever that I have arrived at the conclusion that rubiacine cannot be 

 considered as a true colouring matter, as it is impossible to dye 

 with it. I shall also show that, contrary to the opinion which I was 

 led to entertain in the first instance, rubiacine does not contribute to 

 produce any effect in the process of madder-dyeing. 



On subjecting rubiacate of potash and rubiacic acid to analysis, 

 I obtained the following results : — 



