Dr. Schunck on Rubian and its Products of Decomposition. 223 



silver, perchloride of tin, protonitrale of mercury, perchloride of 

 mercury and chloride of gold produce uo precipitate whatever 

 in a watery solution of pure rubian, nor does any reaction take 

 place, except a darkening of the solution in the case of some of 

 these salts. If the rubian be impure, which is always the case 

 when the solution has been incautiously evaporated and the 

 rubian has been exposed to too great a heat after evaporation, 

 then its solution, though it does not differ in appearance from 

 one of pure rubian, when mixed with any mineral or organic 

 acid, even acetic acid, or the salts of the alkalies or alkaline earths, 

 is rendered milky, and a quantity of dark brown transparent 

 resinous drops, mixed with yellow flocks, are deposited. These 

 drops, in the case of the salts, consist merely of a substance 

 insoluble in saline liquids, which dissolves again in pure water; 

 but in the case of acids, they are, though similar in appearance, 

 a product of decomposition of the latter substance, and do not 

 redissolve in pure water. Sugar of lead gives, in a solution of 

 impure rubian, a dark reddish-brown precipitate. Most me- 

 tallic salts also give precipitates, consisting either of the sub- 

 stance itself which accompanies the rubian, or of compounds of 

 this substance, with the respective metallic oxides. I shall re- 

 turn to these reactions when I come to treat of the action of 

 heat on rubian. Basic acetate of lead gives a copious light red 

 precipitate in a solution of pure rubian, the solution becoming 

 colourless. This is the only definite compound of rubian with 

 a base that I am acquainted with. Concentrated sulphuric acid 

 dissolves rubian with a blood-red colour ; on boiling the solution 

 it becomes black and disengages sulphurous acid gas in abun- 

 dance, after which water precipitates a black carbonaceous mass. 

 If sulphuric acid be added to a watery solution of rubian, and 

 the mixture be boiled, the solution, if dilute, becomes opalescent, 

 and on cooling a quantity of light yellow flocks are deposited ; 

 and if the solution was concentrated, these are formed in such 

 abundance jon cooling as to render the liquid thick. If these 

 flocks exhibit the least tinge of green, the presence of chlorogenine 

 is indicated. Muriatic acid acts in precisely the same manner. 

 Nitric acid produces in the cold no effect in a solution of rubian ; 

 but on boiling, a disengagement of nitrous acid takes place, the 

 liquid becomes light yellow, and now contains the acid which I 

 called in my former papers alizaric acid, and which Laurent 

 and Gerhardt consider as identical with naphthalic acid. Phos- 

 phoric, oxalic, tartaric and acetic acids produce no effect on t lie 

 •olution, even on boiling for gome time. "When a stream of 

 chlorine gai 18 pa- id through a watery solution of rubian, the 

 solution immediately becomes milky mid begins to deposit a 

 lemon-yellow powder, into which, on continuing the action, the 



