ACTION OF NITRIC ACID ON INDIGO. 35Q 



combined, is more fixed. Thus the compound of polash 



with amer detonates more loudly than that of ammonia, and 



less than that of oxide of lead. But there are various cir- Circumstances 



cumstances capable of modifying the strength of the deto- ^^^'^ ™°'^'^y *^* 



nation: 1st, the quantity of amer united with the base: 



2d, the force with which they are combined ; and 3d, the 



nature of the base. Thus, for instance, the metallic oxides 



that are easily reducible form compounds, that detonatemore 



feebly than those that are difhcult of reduction. 



24. The solution of amer precipitates isinglass: but the Amer precF- 

 precipitate is soluble in an excess ef gelatine, and in all P"^'^* gelatine. 

 the acids. This property I shall notice in a subsequent 



paper. 



§ III. Art. 2. Of the Volatile Add. 



25. The orange-coloured matter separated from the resin The oran^e-co- 



by boiling water (10) was little soluble in cold water. '''"''"^ "^^"'^^ » 

 T, .,■ , . - . , , compound. 



iioiliog water separated some resin from it; and the crystals, 



that fell down on cooling, Averc fawn-coloured. These 

 crystals were composed of volatile acid, resi?i, and a small 

 quantity of amer. I purified it in the following manner. The volatile 

 I dissolved 5 gram. [77 grs.] in hot water, added in fi^e ^^'*^ P""^^'^* 

 portions as many grammes of carbonate of lead, boiled and 

 filtered. On the paper was left a yellow powder, consist- 

 ing of resin and a portion of volatile alkali combined with 

 oxide of lead. To the filtered liquor I added sulphuric acid ; 

 and the oxide of lead (with which the volatile acid had 

 combined, forming with it a soluble compound with excess 

 of acid) fell down in the state of sulphate. The liquor I 

 filtered still boiling, evaporated, and obtained by refrigera- 

 tion white acicular crystals, united by their extremities in 

 the form of stars. Having left them to drain, I redissolved 

 them in boiling water, and thus separated a small quantity 

 of resin ; when the crystals obtained by cooling were of a 

 fine white like wax. To obtain these crystals in all their 

 whiteness, care must be taken not to dry them on paper 

 that contains carbonate of lime, or oxide of iron, as this 

 would turn them yellow, or reddish. 



On boiling down the mother water, that had yielded the More obtahied 

 crystals of volatile acid, more crystals of YolatUeacid ^^'"^ [^5"^^^^?** 



depositetl 



