PHYSICAL PROPERTIES OF MINERALS. 125 



Several varieties of Bitumen possess a bituminous odor. Iron 

 Pyrites emits a sulphureous smell when two pieces are forcibly 

 struck together so as to strike fire. Arsenical Iron under the same 

 circumstances gives the odor of garlick. Black Limestone of a ceiv 

 tain kind emits under the blow of the hammer a fetid smell : pieces 

 of Quartz likewise produce a peculiar odor when struck together. 



Sulphuretted Hydrogen, Sulphurous Acid, and oilier natural gases 

 have various odors ; as that of rotten eggs, of burning sulphur, &c. 



Besides the characters treated of in the foregoing pages, there 

 are still some phenomena which have been made use of in the de- 

 scription and discrimination of minerals. Among these, the Adhe- 

 sion to the Tongue is almost exclusively met with in decomposed 

 minerals ; the Unctuous and Meagre Touch are used for distin- 

 guishing certain friable minerals ; and the Phosphorescence pro- 

 duced by heat is also employed in those minerals in which the nat- 

 ural properties are not observable.* 



* Chemical characters. These are made up of the use of the Blowpipe 

 and the action of acids; of which it maybe remarked, that in strictness, 

 it is no more required of a treatise like the present, to describe the man- 

 ner of examining minerals by heat and the reactions of acids, than it is to 

 give the rules observed by the analyst in ascertaining the composition 

 of minerals: the information pertaining to these subjects being the ap- 

 propriate province of Chemistry, and should, of course, be looked for, 

 when sought in detail, in the works on that science. It is only to abridge 

 the inconvenience of reference to other books, and which may not be 

 within the reach of the reader, that the following account is given of 

 these characters. 



BLOWPIPE. The most simple of all blowpipes is that employed by 

 the smiths to direct the flame of a lamp upon small pieces of metal placed 

 on charcoal. It consists of a tapering metallic tube, Fig. 152, ten or 

 twelve inches long, and bent at right angles towards the smaller extrem- 

 ity, where us opening is so small as scarcely to admit a common sized 

 pin ; while at the larger end it varies from one sixth to one fourth of an 

 inch. In the operations of the artist, (which commonly consist in little 

 solders,) the small extremity, or beak, -is brought near the flame of the 

 lamp, and with the mouth, a current of air is impelled through the tube 

 upon the flame. As the blowing is anly required for a moment at a 

 time, no inconvenience arises from the moisture, which is apt to be 

 Driven along with the current of air from the lungs. But in the experv 



n* 



