338 Chemical Examination of Microliie. 



in their construction, to increase their elasticity, we would add, that 

 all springs, which have been subjected to this process, have, for a 

 certain length of tirpe, a decided disposition to accelerate progress- 

 ively ; and it would therefore appear, that some particular change 

 invariably goes on in the spring after the operation of exposure to 

 the 6re, the fiature of which we are at present very imperfectly ac- 

 quainted with ; but, from the few experiments v\^e have made, we 

 are convinced that glass is in every respect capable of being intro- 

 duced into the manufacture of chronometers. 



Art. XVI. — Chemical Examination of Microliie; by Charles 

 Upham Shepard, M. D. Professor of Chemistry in the Medical 

 College of the State of South Carolina. 



For my description of this mineral,* I could command only a few 

 minute crystals, the largest of which weighed but four tenths of a 

 grain. Had these not been possessed of considerable regularity of 

 form and at the same time afforded very uniform results in the de- 

 termination of their hardness and specific gravity, I should not have 

 ventured on referring them to a new mineralogical species. The 

 recent examination however of three crystals of the same substance 

 from Chesterfield, each weighing about five grains, completely estab- 

 lishes the description already given, and enables me to throw some 

 light on the chemical constitution of the species. 



A. A very thin fragment of one of these crystals was heated be- 

 fore the blowpipe ; it turned lemon-yellow at the apex, but without 

 having suffered fusion. The same piece dissolved freely in borax 

 with much effervescence, and formed a colorless, transparent glass. 



B. 24-5 centigrammes of the mineral, in the state of an impalpa- 

 ble powder, were heated to whiteness in a platinum crucible. It 

 lost 0-5 centigramme ; i. e. 2-04 p. c. 



C. Another portion in powder was treated with sulphuric acid 

 in a glass tube, and heat applied. No perceptible corrosion of the 

 glass was observed. 



D. A few centigrammes were digested, first in dilute hydrochloric 

 acid and afterwards in dilute agua-regia during several hours. The 

 mineral was not sensibly attacked. 



* American Journal of Science and Arts, vol. xxvii. p. 361, and my Treatise on 

 Mineralogy, Part second, vol. ii. p. 45. 



