202 Dr. Schunck on Rubian and its Products of Decomposition, 



baryta made from chloride of barium and bicarbonate of soda, 

 and evaporating in contact with the air until red flocks begin to 

 appear, or by adding caustic baryta to the solution, allowing the 

 mixture to stand exposed to the air for some time and filtering, 

 when the insoluble baryta compound left on the filter will yield 

 rubianic acid and rubidehydran, and the liquid rubihydran. 

 The same process of decomposition takes place, if caustic soda, 

 ammonia, or lime water be added to a wateiy solution of rubian, 

 and the mixtures be allowed to stand exposed to the air for 

 some time. On now adding chloride of barium to any one of 

 them a dark red precipitate falls, which being collected on a 

 filter, washed with water and then treated in the same manner 

 as the red flocks obtained by means of bicarbonate of baryta, 

 afibrds in each case rubianic acid and rubidehydran, while the 

 liquid contains rubihydran. If a small quantity of any acid be 

 added to a watery solution of rubian, and if the acid be then 

 neutralized with carbonate of baryta, the small quantity of 

 bicarbonate of baryta formed is sufficient to induce a decom- 

 position of the rubian, for the filtered solution on exposure to 

 the air very soon begins to deposit red flocks, which consist of 

 rubianic acid and rubidehydran in combination with baryta. It 

 is for this reason that I have recommended the employment of 

 carbonate of lead instead of carbonate of baryta for the purpose 

 of neutralizing the sulphuric acid used in purifying rubian*. 

 Even oxide of lead is a sufficiently strong base to cause rubian 

 to undergo this process of decomposition, when oxygen is pre- 

 sent at the same time. If rubian be precipitated from its 

 watery solution by means of basic acetate of lead, and the lead 

 compound be left exposed to the air for a short time, it will be 

 found no longer to contain unchanged rubiuu. If the com- 

 pound be decomposed with sulphuric acid in the cold, and the 

 excess of acid be neutralized with carbonate of lead, the filtered 

 solution deposits during evaporation crystals of rubianic acid, 

 and leaves at last a brown deliquescent mass, which unless it be 

 strongly dried is with difficulty removed from the vessel con- 

 taining itf. In short, whenever rubian is brought into contact 

 at the same time with oxygen and an alkaline or other strong 

 base, it undergoes decomposition. Hence it follows, that in 

 preparing the so-called xanthine according to the methods pro- 



* See Phil. Mag. for March 1862, p. 222. 



t In purifying i-ubian by precipitation with basic acetate of lead, as de- 

 scribed in the first part of this paper, care must be taken to wash the pre- 

 cipitate with alcohol and not with water. If the former be employed, de- 

 composition is almost entirely prevented, whereas in using water the rubian 

 in the precipitate imdergoes complete decomposition during the short time 

 necessary for edulcoration. 



