48 



CHEMISTRY. 



Chloride of Sodium j g^j /^^"^ z ^ Hydrochloric acid gas. 



Sulphuric acid "~""^^^^^^'<Cr'' 



Water \ Hydrogen ^^'^^'^'"'■^^-^^^II::::^:-^.^ 



( Oxygen —11=:^^-^ Sulphate of Soda. 



Prop. — A colourless gas; gives off dense fumes on exposure to 

 the air; has a very powerful affinity for water, and hence must be 

 collected over mercury; condensed into a liquid by a pressure of 

 40 atmospheres; sp. gr. 1-269; water absorbs 418 times its bulk. 



The solution of this gas in water constitutes the muriatic acid of 

 commerce. This, when pure, is colourless ; but usually has a light 

 straw colour — due to impurities. When mixed with nitric acid it 

 forms aqua regia, which has the property of dissolving gold, in conse- 

 quence of the chlorine evolved; water and nitrous acid are also 

 formed at the same time. 



Hydrogen and Iodine. — Hydrioddc acid, HI. — A gas much resem- 

 bling hydrochloric acid; — prepared by heating water in union with 

 iodide of phosphorus ; the hydrogen combines with the iodine to form 

 hydriodic acid, and the oxygen with the phosphorus to form phos- 

 phoric acid. 



Prop. — Colourless, acid ; has a strong affinity for moisture, and 

 gives out white fumes in the air. It is decomposed by chlorine, with 

 the formation of hydrochloric acid and evolution of iodine; sulphuric 

 and nitric acid also decompose it by imparting oxygen, likewise 

 evolving iodine. 



Hydrogen and Bromine. — Hydrobromic acid^ HBr; — prepared 

 like hydriodic acid, from a bromide of phosphorus. 



Prop. — A colourless gas, irrespirable, and acid; is decomposed by 

 chlorine, but not by iodine. 



Hydrogen and Fluorine. — Hydrofluoric acid, HF ; — prepared by 

 the action of dilute sulphuric acid on fluoride of calcium (fluor spar); 

 the chemical changes are analogous to those occurring in the pre- 

 paration of hydrochloric acid. 



Prop. — At 32° it is a colourless liquid, but when exposed to the 

 air, it flies off in dense white fumes; sp. gr. 1*0609; — its affinity for 

 water surpasses even that of sulphuric acid, the combination being 

 accompanied with a hissing noise; its vapour is extremely pungent; 

 it is very destructive to organized bodies, as the skin, upon which it 

 produces a deep and painful ulcer. It acts powerfully on glass, 

 forming with it fluosilicic acid ; on this account it must be prepared 

 in metallic vessels. From its affinity for glass, it may be used for 

 etching on that substance; the glass being coated with a thin film 

 of wax and the figures traced with a pointed instrument ; it is then 

 submitted to the action of the gas which, acting only on the exposed 

 portions of the glass, leaves an indelible mark upon them. 



