94 Mr. Brande’s chemical Experiments 
This brown substance appears to be guaiacum, the pro- 
perties of which are materially altered, by its combination 
with oxygen ; and I am led to think that the changes of 
colour produced by nitric and oxy-muriatic acids, are the 
consequence of the different proportions of oxygen with 
which the guaiacum has been united ; for we know that the 
colours of metallic, and many other bodies, are greatly in- 
fluenced by the same cause. 
The brown substance was separated by filtration ; the fil- 
trated liquor yielded yellow flocculent precipitates with the 
alkalis, and on examination was found to hold nitrate of lime 
in solution. 
The undissolved portion was of a deep chocolate-brown 
colour. A. similar substance may also be obtained, by eva- 
porating the recent nitric solution to dryness, taking care not 
to apply too much heat towards the end of the process. 
The substance obtained by either of these means, possesses 
the properties of a resin in greater perfection than guaiacum ; 
it is equally soluble in alcohol and sulphuric ether, insoluble in 
water, &c. ; but when burned it emits a peculiar smell, more 
resembling animal than vegetable bodies. If, however, fresh 
portions of nit ric acid be added three or four times succes- 
sively ; or if a large quantity be employed to form the 
solution ; the product obtained by evaporation is then of a 
very different nature ; for it has lost all the characteristic 
properties of a resin, having become equally soluble in water 
and alcohol ; the soli ion of it in this state having an astringent 
bitter taste.* 
* Vide Mr. Hatchett’s two Papers on an artificial Substance which possesses 
the principal characteristic Properties of Tannin. Phil. Trans. 1805, p. 21 1, and 285. 
