330 Prof. Johnston on the Composition of certain 



fracture, not compact, but as if made up of many small por- 

 tions adhering together. The other variety is mixed with a 

 greater or less quantity of a dark brown, bituminous-like 

 substance interposed between the small fragments of which 

 the mass is composed. 



The pure mineral is opake, of a pale yellow colour, yields 

 easily to the knife, may be rubbed to powder ; is very slightly 

 soluble in water, and largely in alcohol, giving yellow solu- 

 tions which have an intensely hitter taste. This last property 

 is highly characteristic. By slow evaporation the alcoholic 

 solution yields pale yellow prisms. As it occurs in nature, 

 the Guyaquillite has a sp. gr. of 1*092; after fusion, it may 

 possibly be a little heavier. 



It begins to melt at ] 57° Fahr., but continues viscid, and 

 does not flow easily till near 212°. As it cools it adheres to 

 the finger and exhibits much tenacity, forming fine threads 

 when drawn out. After fusion it is semitransparent, a little 

 darker in colour, and exhibits the resinous fracture and lustre. 

 Heated in a close tube over a lamp, it darkens, is decomposed, 

 and yields empyreumatic products. 



It dissolves readily in a dilute solution of caustic potash and 

 less so in caustic ammonia, giving yellow solutions, from which 

 it is again precipitated by an acid. Sulphuric acid of com- 

 merce dissolves it in the cold, giving a dark reddish brown 

 solution, from which water throws down the resin apparently 

 unchanged. Muriatic acid boiled over it becomes yellow, but 

 dissolves very little and does not appear to alter it. Strong 

 nitric acid by the aid of heat acts upon it with the evolution of 

 red fumes, becoming yellow. It dissolves it, however, in small 

 quantity only, and the solution becomes milky as it cools, and 

 deposits white flocks. It is also precipitated white by the 

 addition of water. I have had too little of the substance to 

 permit me further to investigate the nature of the change 

 produced by this acid. 



The action of liquid ammonia on the alcoholic solution of 

 this substance is characteristic. The pale yellow solution, by 

 the addition of a few drops of ammonia, gradually darkens, 

 and ultimately becomes dark brownish red. The alcoholic 

 solution gives a yellow precipitate, with a similar solution of 

 acetate of lead. With one of nitrate of silver it gives at first 

 none, but after standing for several hours a small quantity of 

 a very dark precipitate shows itself. The addition of am- 

 monia determines a brown precipitate, which speedily darkens 

 and assumes a deep purple or black colour. This mineral 

 substance, therefore, like the resin of retin asphalt (retinic 

 acid), belongs to the class of acid resins. 



