266 Mr. Schunck on the Substances 



precipitating basic acetate of lead, reducing chloride of gold, 

 and giving a red colour with ammonia and red flocks on 

 boiling with nitric acid. Erythric acid then, like lecanoric, 

 is converted by alkalies into orcine and carbonic acid. A so- 

 lution of erythric acid in ammonia exposed to the air soon 

 becomes of a dark-red or purple colour. It is the basis, and 

 I believe the only one, of the colouring matters derived from 

 the plant. An alcoholic solution of erythric acid, is not pre- 

 cipitated by nitrate of silver, but the addition of nitrate of 

 silver to an ammoniacal solution produces a white precipitate, 

 which on boiling becomes black, a mirror of silver being 

 formed at the same time on the sides of the glass. Chloride 

 of gold added to an alcoholic solution is not changed even on 

 boiling. With perchloride of iron an alcoholic solution strikes 

 a deep purple colour ; on the addition of ammonia the colour 

 is changed into yellow, but the oxide of iron is not precipi- 

 tated, unless the fluid be boiled. It is not precipitated by 

 an alcoholic solution of acetate of lead, but basic acetate of 

 lead produces immediately a copious precipitate. 



On combustion with oxide of copper the following results 

 were obtained : — 



I. 0-5400 grm. dried at 212° gave 1-1640 carbonic acid 

 and 0-2530 water. 



II. 0-3640 grm. gave 0*7835 carbonic acid and 0-1820 

 water. 



These numbers lead to the following composition : — 



34 equivs. Carbon . 2550*0 



19 ... Hydrogen 237*5 



15 ... Oxygen . 1500-0 



4287-5 



The lead compound was prepared by precipitating an alco- 

 holic solution of erythric acid with basic acetate of lead, 

 filtering, washing the precipitate with cold water and drying 

 in vacuo. 



I. 0*6340 grm. gave 0*6435 carbonic acid and 0*1215 water. 

 0*3465 gave 0*0075 lead and 0*1970 oxide of lead. 



II. 0*3195 grm. gave 0*3160 carbonic acid and 0*0630 water. 

 0*4345 gave 6*0945 lead and 0*2520 oxide of lead. 



This gives — 



9415*5 100*00 100*00 100*00 



