So) SoS not 5 2! pa BN ei mee 
San oe ea ha ee a 
Mineralogy and Geology. 349 
‘slightly discolored, it appeared to be feebly negative. Rosin, pitch, 
‘gum lac, and amber, both with the paper and the cotton, became always 
‘Positive, as did also the native rubber, by which I mean the rubber as 
itis imported. Sealing-wax with the cotton became always positive, 
used in making gas bags) would sometimes become positive and some- 
‘times negative, and the e was true of gutta percha, two different 
* . 
: = Was even fearful that it might become ignited by the sparks pro- 
duced | 
they shall have returned to their natural condition at all points. Some- 
‘times a substance when first rubbed, after having remained undisturbed 
‘wenty-four hours or more, will take on one electricity, but, by continu- 
ing the friction a very little time, it will take on the other. Thus, a 
Stick of sealing-wax in its natural state, when gentl rubbed, one or two 
strokes, with a silk handkerchief, will often be found decidedly positive, 
it by a few strokes more it will become as decidedly negative; and it 
cannot be made positive again by friction with silk until allowed by re- 
Pose first to return to its natural state. 
II. MINERALOGY AND GEOLOGY. 
1. On Tin Ore at Durango in Mexico ; by Prof. C. F. CHANDLER.— 
‘ Thave Tecently examined a sample of 1450 grams of tin ore from Du- 
r, some of the crystals might easily be mistaken for cassiterite. 
_ AX Jour. Sct.—geconp Sunms, Vou. XXXIX, No. 117.—May, 1865. 
45 
