Sulphuric acid 49 _grm._ SO_{4}H_{2} = 40 _grm._ SO_{3} Hydrochloric acid 36·5 " ClH = 35·5 _grm._ Cl. [G]Oxalic acid 63·0 " C_{2}O_{4}H_{2} + 2 Aq. Acetic " 60·0 " C_{2}H_{3}O_{2}H. Soda 40·0 " NaHO. Sodic carbonate 53·0 " Na_{2}CO_{3}. [G]Lime 28·0 " CaO = 37·0 _grm._ CaH_{2}O_{2}. [G]Calcic carbonate 50·0 " CaCO_{3}. Ammonia 17·0 " NH_{3}. [G]Barium hydrate 76·5 " BaO = 85·5 _grm._ BaH_{2}O_{2}. Barium chloride 104·0 " BaCl_{2}. Zinc chloride or sulphate 32·6 " Zn = 16·0 _grm._ S. as sulphide. Silver nitrate 170·0 " AgNO_{3} = 35·5 _grm._ Cl. Potassic permanganate 31·6 " K_{2}MnO_{4}. [Footnote G: Insufficiently soluble in water to form a normal solution.] EXAMINATION OF WATER. _Hardness_ (Hehner's process). (_a_) Temporary Hardness.--As has been stated (p. 84), this consists of lime and magnesia carbonates. As methyl orange is not affected by carbonic acid, bicarbonates of alkaline earths have an alkaline reaction, and may be estimated in solution by standard acid like the alkalies themselves. 100 _c.c._, or in soft waters 200 _c.c._, of the water is measured into a beaker, a drop or two of solution of methyl orange added, and decinormal hydrochloric or sulphuric acid run in from the burette with constant stirring till the colour just changes to pink. This is repeated, and the average taken. The two determinations should not at the most differ more than 1/10 _c.c._ Each _c.c._ represents 5 parts per 100,000 of CaCO_{3} or 2·8 parts of CaO; or corresponding quantities of magnesia (4·2 parts of MgCO_{3} or 2 parts MgO), when 100 _c.c._ of water are used.