198 Mr. T. Taylor on some 



coal : they are hard, brittle, and easily reduced to powder, in- 

 odorous, and have a bitter resinous taste ; their summits are 

 generally quite flat, but are sometimes bevelled at their edges. 

 Three-sided prisms are occasionally deposited, which appa- 

 rently result from an extension of each alternate face of the 

 six-sided prism. 



The crystallized acid fuses at 4-01° Fahrenheit, and when 

 not heated beyond that temperature becomes on cooling an 

 opake crystalline mass. If the fused acid be heated only a 

 few degrees above 401° Fahrenheit, it forms when cold a trans- 

 parent glass, without the slightest trace of crystalline struc- 

 ture : when alcohol is poured over the fused mass a number 

 of minute cracks are suddenly formed, which possess consider- 

 able regularity. If a thin layer of alcohol is allowed to re- 

 main over it, the whole is quickly converted into an aggre- 

 gated mass of regular crystals. The most remarkable circum- 

 stance is that the melting-point of the vitreous or amorphous 

 resino-bezoardic acid is nearly 180° lower than that of the 

 crystallized acid, Prof. Wbhler having determined that the 

 crystallized acid melts at 400° Fahrenheit, while the amor- 

 phous fuses at a temperature between 220° and 230° Fahren- 

 heit. In this respect resino-bezoardic acid resembles sugar, 

 sulphur, amygdaline and silvic acid ; all of which bodies have 

 two distinct fusing-points, according as they are either in a 

 crystalline or amorphous state : this property Wohler believes 

 to be possessed by all dimorphous bodies. The above fact 

 may be readily observed in the following manner, which serves 

 as a very characteristic test of resino-bezoardic acid. Let a 

 few grains of the powdered resin be strewed over a thin slip 

 of glass and held over the flame of a candle until a portion 

 only of the resin is melted : if the edges of the semi- fused 

 portion be examined by the microscope groups of very regu- 

 lar six-sided plates are seen ; the perfectly fused portion is 

 glassy and devoid of crystalline structure. This test does not 

 always succeed with the raw calculus, owing to the foreign sub- 

 stances which it contains. When heated beyond its melting- 

 point this acid gives off* white vapours, which have an aro- 

 matic odour ; it finally catches fire and burns like resinous 

 bodies in general. 



Resino-bezoardic acid is insoluble in water and muriatic 

 acid. It is thrown down from its alcoholic solution by water 

 as a white precipitate, which under the microscope appears in 

 the form of small prismatic crystals arranged in stellate groups. 

 It is readily soluble in a solution of potass, soda, ammonia, 

 and carbonate of ammonia, and is precipitated on the addi- 

 tion of an acid. The precipitate at first forms a dense white 



