Dr. Schunck on Rubian and its Products of Decomposition. 211 



Another specimen of the lead salt, prepared by precipitating 

 an alcoholic solution of the acid with an alcoholic solution of 

 basic acetate of lead, was found to have a composition agreeing 

 tolerably well with the formula C^^ h^s Q^s + 9PbO. When this 

 precipitate was redissolved in a mixture of alcohol and acetic 

 acid, and a fresh precipitate was produced by means of a little 

 ammonia, the latter was found to contain acid and oxide of lead 

 in the proportion of 1 equiv. of the former to 6 equivs. of the 

 latter. It appears, therefore, that these lead precipitates are by 

 no means uniform in composition. 



The silver salt was obtained by dissolving the acid in boiling 

 water, adding a small quantity of ammonia and then nitrate of 

 silver, when it fell in the form of a dark chocolate-coloured floc- 

 culent precipitate, which, when viewed under a lens, was some- 

 times seen to consist Of small crystalline needles. The preci- 

 pitate was collected on a filter and slightly washed with water. 

 As it was found to dissolve in water with a reddish-brown colour, 

 as soon as the excess of nitrate of silver was removed, the edul- 

 coration was completed with alcohol, in which the salt is insoluble. 

 After being dried in vacuo — 



0*6300 grm. gave 0*1370 grm. chloride of silver, equivalent 

 to 0-11076 or 17*58 per cent, of oxide of silver. The formula 

 C52H28 0^+AgO requires 17*47 per cent. 



The alizarine and sugar obtained by the decomposition of 

 rubianic acid with acids and alkalies, I found to have the usual 

 composition, as the following analyses will show : — 



I. 0*2190 grm. alizarine, obtained by the action of sulphuric 

 acid on rubianic acid, dried at 100° C, yielded 0*5550 carbonic 

 acid and 0*0850 water. 



II. 0*3320 grm. alizarine, formed by the decomposition of 

 rubianic acid with caustic soda, dried at 100° C, gave 0*8480 

 carbonic acid and 0*1195 water. 



These numbers give in 100 parts — 



The sugar derived from the decomposition of rubianic acid with 

 sulphuric acid was prepared for analysis by heating it, after the 

 solution had been evaporated to a syrup, for some time at 100°C. 

 until it became sufficiently brittle to be pulverized, when 



0*3600 grm. yielded 0*5840 carbonic acid and 0*2060 water, 

 corresponding with the following composition : — 



P2 



