OF SILVER. 405 



measured as carefully as possible with the com- 

 mon goniometer, are 70 37', and 109 23'. The 

 usual plates in which its crystals appear, if at- 

 tentively examined, show clearly enough that 

 the shape is rhomboidal, and the angles of the 

 larger faces may easily be observed ; but, by 

 spontaneous crystallization, I have obtained large 

 and very regular crystals though the faces were 

 not smooth enough to admit of measurement by 

 the reflecting goniometer. The properties of 

 this salt are sufficiently known. It dissolves in 

 its own weight of cold water, and in about four 

 times its weight of alcohol. Its taste is exceed- 

 ingly acrid, and it constitutes a violent poison. 

 When heated it melts, and, on cooling, congeals in- 

 to a mass of a grey colour, and composed of small 

 needle-form crystals. In this state it is used by sur- 

 geons as an escharotic, under the name of lunar 

 caustic. I have never yet met with lunar caustic, 

 as it is prepared for sale, absolutely pure. It al- 

 ways contains some gold, and often a little cop- 

 per. Both of these metals separate in dark flocks 

 when the caustic is dissolved in water. Not un- 

 frequently it contains nitrate of potash ; and 

 perhaps there may be other occasional impuri- 

 ties, which I have not detected. This salt is an- 

 hydrous, both when crystallized and in the state 

 of lunar caustic. 21-5 grains of the crystals, 

 dried upon blotting paper, when kept for 20 

 minutes in a state of fusion in a platinum cru- 



Cc3 



