LESSONS IN CHEMISTRY. 



181 



for five or six weeks, then packed with alternate layers of coarsely 

 ground oak or hemlock bark and covered with water for six or 

 eight months, changing them occasionally so that all shall be 

 treated by a uniform strength of the tannic acid. By this time 

 the hide or skin has increased in weight from 30 to 40 per cent., 

 has acquired a uniform brown color and is chemically leather, 

 ready for various mechanical operations which give it the de- 

 sired texture and finish. Special processes are used in preparing 

 kidskins, buckskins, etc. Tannic acid is used in medicine. 



Morphine obtained from opium, quinine derived from Peruvian 

 bark, both used extensively in medicine, are vegetable alkaloids. 

 Strychnine from nux vomica, and nicotine from tobacco, two of 

 the most active poisons, are alkaloids, as are theine and caffeine, 

 the active elements of tea and coffee. 



A list of the more important elements, with the symbol and 

 combining or atomic weight of each. 



NON-METALLIC ELEMENTS. 



Name. Symbol. Weight. 



Oxygen O 15.96 



Hydrogen H 1.00 



Nitrogen N 14.00 



Chlorine Cl 35.36 



Bromine Br 79.75 



Iodine I 126.53 



Fluroine.... ...F 19.10 



Name. Symbol. 



Carbon C 



Silicon Si 



Boron B 



Sulphur S 



Phosphorus P 



Arsenic... ...As 



Weight. 

 12.00 

 28.00 

 11.00 

 31.98 

 30.96 

 74.90 



METALLIC ELEMENTS. 



Potassium (Kalium)...K 39.04 



Sodium (Natrium) Na 23.00 



Lithium Li 7.01 



Calcium Ca 39.90 



Barium Ba 136.80 



Strontium Sr 87.20 



Aluminium A! 27.30 



Magnesium Mg 23.94 



Zinc Zn 64.90 



Silver (Argentum) Ag 107.66 



Copper (Cuprum). .^....Cu 63.30 



Mercury (Hydrargyrum) Hg 



Iron (Ferrum) Fe 



Nickel Ni 



Cobalt Co 



Manganese Mn 



Chromium Cr 



Bismuth Bi 



Lead (Plumbum) Pb 



Tin (Stannum) Sn 



Gold (Aurum) Au 



Platinum..., ...Pt 



199.80 



55.90 



58.60 



58.60 



54.80 



52.40 



207.50 



206.40 



117.80 



196.20 



196.70 



