Dr. Will on Oil of Rue: Erdman on Indigo. 207 



potash forms a peculiar acid, = camphor + water. C^H'^O- 

 forms C'" H's O^ 



A tabular view of several acids, with their hypothetical 

 types, which here follow, we have not thought necessary to 

 add; the above short extract of this very important paper is 

 only an outline, those who wish for more information must 

 refer to the original paper. 



The oil obtained by distilling the fresh plants of Ruta 

 graveolens is yellowish-green, smells like the plants, tastes 

 bitter and aromatic; sp. gr. = 0"837 at 18° C. If allowed to 

 stand some time over chloride of calcium and then distilled, it 

 boils at 218°, and the boiling point rose to 24>5°. The sp. gr. 

 of the colourless product varies from 0"831 to 0'838. Ra- 

 tional formula C-** H-^ -f O^. Specific gravity of the vapour 

 was found to be 7*892, ought to be 7'690; therefore the atom 

 is equal to four volumes. The oil is soluble in sulphuric 

 acid, and is precipitated by water ; hydrochloric acid gas has 

 no action; by chlorine and nitric acid it is decomposed. 

 These experiments have been made by Dr. H. Will in 

 Giessen. (Annaleii der Pharmacie, xxxv. 235.^ 



Erdmann has examined the action of chlorine and bromine 

 on indigo. The indigo-blue used for these experiments con- 

 tained a little indigo-red, which is, however, of no consequence. 

 Dumas's formula for indigo-blue is C"' H^ N 0-; Erdmann's 

 is C^- H'" N- O'. When chlorine is passed into indigo-blue 

 suspended in water, the blue colour changes to a grayish- 

 green, and then to yellow. Hydrochloric acid remains in 

 solution. It is best to employ a low temperature. When 

 this mass is distilled with water a volatile substance passes 

 over; it is called chlorindopten, or chloride of indopten j it 

 is formed in very minute quantities; it may be purified by 

 repeated distillations with water and sublimation ; it is then 

 obtained in the form of fine needles of a peculiar unpleasant 

 smell; fuses to a colourless oil; is»not very volatile; soluble in 

 hot water, but very little in cold; soluble in alcohol. Formula 

 C" H ' CI- O. It is, however, a compound of two substances. 

 When heated with caustic potassa or its carbonate the dis- 

 agreeable smell disappears, a substance passes over similar in 

 appearance to chloride of indoplen, but differing from it in 

 not giving a sour solution with water. Erdmann calls it 

 chlorindatmit(!), from uTfJuis. It is formed in very small quan- 

 tities; its formula is C'-H*C1'0'. The residue, after di- 

 stilling off" the chlorimlatmit, is crystalline, soluble in water, 

 less so in alcohol ; it is allowed to stand in the air and then 

 extracted with alcohol. Out of this solution acids precipitate 



