contained in the Roccella tinctoria. 269 



easily in boiling water. Its solution in the latter, however, does 

 not re-deposit it on cooling. On evaporating a solution of it 

 in water or alcohol, it is left behind as a white crystalline 

 mass, but never in well-defined crystals or needles. Its so- 

 lutions redden litmus paper slightly. It does not undergo 

 any further change on being treated with boiling water, nor 

 does it form an aether on being treated with boiling alcohol, 

 as erythric acid does ; it has therefore little or no claim to be 

 considered as an acid. Heated on platinum 'foil it melts to a 

 yellow fluid, is decomposed, and burns with a bright flame, 

 leaving no ash. Heated in a tube closed at one end it gives 

 a sublimate of orcine. It is decomposed by boiling nitric acid 

 with an evolution of nitrous acid. Concentrated sulphuric 

 acid dissolves it, and on boiling decomposes it with a disen- 

 gagement of sulphurous acid. It dissolves in caustic alkalies, 

 and in lime and baryta water in the cold. Its solution in 

 baryta water deposits carbonate of baryta on boiling, and the 

 solution then contains nothing but orcine. Its solutions in 

 alkalies speedily become red on exposure to the air. Its aque- 

 ous solution is not precipitated by neutral acetate, but copi- 

 ously by basic acetate of lead. With perchloride of iron it 

 gives a deep purple colour, which is destroyed by ammonia, 

 the oxide of iron being immediately precipitated. Nitrate of 

 silver is not changed by it on boiling, but on the addition of 

 ammonia a precipitate is produced, which on boiling the fluid 

 is reduced, the silver being deposited as a metallic mirror on 

 the sides of the glass. Chloride of gold is slowly reduced by 

 it on boiling, the gold being deposited in the shape of metallic 

 scales ; if caustic potash be added the reduction is effected 

 instantaneously, the gold being deposited as a black powder. 

 It gives no precipitate with a solution of glue. Its analysis 

 gave the following : — 



I. 0*5090 grm. gave 0*9830 carbonic acid and 0*2850 water. 

 II. 0*4690 grm. gave 0*8970 carbonic acid and 0*2510 water. 



These numbers give the following composition : — 



The compound with oxide of lead, prepared by precipita- 

 tion with basic acetate of lead, gave the following results : — 



0*2575 grm. gave 0*1465 carbonic acid and 0*0430 water. 



0*3185 grm. gave 0*0220 lead and 0*1960 oxide of lead. 

 This corresponds to — 



