40 



CHEMISTRY. 



rable ; sp. gr. 1-524. It may be condensed into a liquid at 32° by 

 a pressure of 36 atmospheres ; this liquid may be frozen by the cold 

 produced by its own evaporation, which is estimated. at 148°. The 

 liquified acid is colourless, and limpid like water ; the solid acid re- 

 sembles snow. Carbonic acid acts upon animals as a poison, pro- 

 ducing asphyxia ; it is injurious even when largely diluted with air; 

 hence the evils resulting from imperfect ventilation. It sometimes 

 accumulates in wells and mines, constituting the choke-damp of 

 miners. Water absorbs its own volume of this gas, at any pressure ; 

 consequently the amount absorbed is determined simply by the de- 

 gree of pressure to which the gas is subjected ; in this way carbonic 

 acid water is manufactured. Carbonic acid exists in the air, as has 

 been mentioned ; also in common spring water, which owes to it its 

 pleasant flavour; the gas maybe entirely driven off by boiling; 

 hence water which has been boiled is quite insipid. 



The best test for carbonic acid is lime-water^ to which it always 

 imparts a cloudiness, resulting from the formation of carbonate of 

 lime. This may seen also by breathing through a tube immersed in 

 lime-water. 



SULPHUR. 



Is found uncombined in the neighbourhood of volcanoes, as in 

 Italy and Sicily ; also abundantly in a state of combination with 

 various metals, as iron, lead, copper, antimony, &c., constituting 

 the pijrites of mineralogists ; procured by exposing iron pyrites to a 

 red heat in close vessels. 



Prop. — A yellow brittle solid, without odour and taste, under 

 ordinary circumstances, but acquires a peculiar odour when rubbed ; 

 sp. gr. 1-99; a non-conductor of heat and electricity; melts at 

 232°, at which point it is a liquid of an amber colour. If the heat be 

 increased, it begins to thicken and acquires a reddish tint ; between 

 428" and 482°, it is thickest ; and beyond this it again becomes 

 thinner up to its boiling point, 600° ; burns when heated up to 300° 

 in the open air. The roll brimstone of commerce, is melted sulphur 

 run into cylindrical moulds. Floicers o? sidphur diVe minute crystals 

 of sulphur, obtained by subliming sulphur in close vessels. The 

 sp. gr. of the vapour is 6-654. The vapour will support combustion. 

 Crystals of sulphur may be procured by melting any quantity in an 

 earthen vessel, and when partially cooled, breaking the crust and 

 pouring out the liquid contents. Crystals are often found on break- 

 ing the roll brimstone of commerce. 



Sulphur is insoluble in water ; soluble in the fixed and volatile 

 oils; — the best solvent is the bisulphuret of carbon ; it dissolves in 

 alcohol if both substances are brought together in the state of vapour. 

 Eq. =16. Symb. S. 



