220 Dr. Schunck on Colouring Matters. 



which consists of the carbonates of lime, magnesia and potash. It is 

 without doubt the acetates of those bases which, being mixed with 

 the substance, produce the smell of aceton during ignition. The 

 acetic acid was of course derived from the basic acetate of lead 

 used in the preparation of xanthine, and the acid with which they 

 were originally combined must have gone to the oxide of lead. 

 Now, as I stated above, the oxide of lead was found to be combined 

 with phosphoric acid ; hence it is probable that the greater part, 

 if not all, of the fixed bases left after the ignition of the xanthine 

 existed in the plant as phosphates. Xanthine has a disagreeable taste, 

 between bitter and sweet. The watery solution is yellow. It is 

 soluble in alcohol, and is left after evaporation in the same state 

 as before. It is insoluble in aether. On adding muriatic or sulphuric 

 acid to the watery solution and boiling for some time, a peculiar 

 smell is evolved, the solution becomes gradually dark green, and a 

 dark green powder is deposited. This is the most characteristic 

 property of xanthine. Nitric acid does not produce the same dark 

 green powder, or any deposit on boiling ; nevertheless the powder 

 which has once been formed by means of muriatic or sulphuric acid, 

 is not dissolved by boiling nitric acid, but only turned yellow. 

 Acetic acid produces no effect. Oxalic acid gives a white preci- 

 pitate of oxalate of lime. Bichromate of potash and sulphuric acid 

 produce no effect on a solution of xanthine, even on boiling. On 

 adding caustic potash to the solution it turns brown, and on boiling 

 a slight smell of ammonia is evolved. Lime and baryta water, 

 acetate and basic acetate of lead, the acetates of alumina, iron and 

 copper, nitrate of silver, corrosive sublimate, and a solution of glue, 

 produce no precipitate or effect whatever in a solution of xanthine. 

 In fact it does not seem to be precipitated by any reagent whatever 

 without undergoing decomposition. 



a a clear light yellow watery solution of xanthine be evaporated 

 with the assistance of heat and in contact with the air, as on the 

 sand-bath, to a syrup, and this syrup be again mixed with water 

 and the solution again evaporated, the process being several times 

 repeated, the solution gradually becomes dark brown, and at length 

 a dark brown powder is deposited. The brown solution now gives 

 with acetate, or basic acetate of lead, a thick brown precipitate. The 

 filtered liquid is yellow, and if the excess of lead be removed by 

 sulphuretted hydrogen, the solution again gives, on evaporation 

 over sulphuric acid, a colourless or light yellow syrup, which how- 

 ever, if redissolved and evaporated with the assistance of heat as 

 before, again becomes dark brown, and deposits a dark brown pow- 

 der. There can therefore be no doubt that this brown powder is a 

 product of the oxidation of xanthine, that xanthine is a species of 

 extractive matter, and that the brown powder stands in the relation 

 to it of an apothema. This brown powder has the following pro- 

 perties : — When dry it is a dark brown mass, easily reduced to pow- 

 der. It is quite insoluble in boiling water and boiling alcohol. It 

 burns without flame, leaving much ash. It is soluble in concentrated 



