| Rubidium | Ru | 104·4 | 11·4 | | Selenium | Se | 79·5 | 4·78 | | Silicon | Si | 28·0 | 2·49 | | Silver (Argentum) | Ag | 108·0 | 10·5 | | Sodium (Natrium) | Na | 23·0 | 0·972 | | Strontium | Sr | 87·6 | 2·54 | | Sulphur | S | 32·0 | 2·05 | | Tantalium | Ta | 182·0 | 10·78 | | Tellurium | Te | 129·0 | 6·02 | | Thallium | Tl | 204·0 | 11·91 | | Thorium | Th | 115·7 | 7·8 | | Tin (Stannum) | Sn | 118·0 | 7·28 | | Titanium | Ti | 50·0 | 4·3 | | Tungsten (Wolfram) | W | 184·0 | 7·5 | | Uranium | U | 120·0 | 18·4 | | Vanadium | V | 51·3 | 5·50 | | Yttrium | Y | 61·7 | -- | | Zinc | Zn | 65·0 | 7·14 | | Zirconium | Zr | 89·5 | 4·15 | +----------------------+---------+--------+-----------+ The figures indicating the proportions by weight in which the elements unite with one another are called the combining or atomic weights, because they represent the relative weights of the atoms of the different elements. Since hydrogen is the lightest element, it is taken as the standard, and its combining or atomic weight = 1. _To find the proportional parts by weight of the elements of any substance whose chemical formula is known_: RULE.--Multiply together the equivalent and the exponent of each element of the compound; the product will be the proportion by weight of that element in the substance. _Example_:--Find the proportional weights of the elements of Alcohol C₂H₆O. Carbon C₂ = equivalent 12 × exponent 2 = 24 Hydrogen H₆ = ” 1 × ” 6 = 6 Oxygen O = ” 16 × ” 1 = 16 Of every 46 lb. of Alcohol, 6 lb. will be H; 16, O; 24, C. To find the proportions by _volume_, divide by the specific gravity. COMMON NAMES OF CHEMICAL SUBSTANCES. _Common Names._ _Chemical Names._ Aqua fortis Nitric acid. Aqua regia Nitro-hydrochloric acid. Blue vitriol Sulphate of copper. Cream of tartar Bi-tartrate of potassium. Calomel Chloride of mercury. Chalk Carbonate of calcium. Caustic potash Hydrate of potassium Chloroform Chloride of formyl. Common salt Chloride of sodium. Copperas, or green vitriol Sulphate of iron. Corrosive sublimate Bi-chloride of mercury. Dry alum Sulphate of aluminium and potassium.