The Chemistry Of Common Things.

greatest quantity and purity from the salt called chlorate of potash . When heated , this substance eA'olves oxygen copiously . It is usual to mix a little oxide of manganese Avith it , in order that the gas may be more readily disengaged . A small quantity of the salt should bo placed in a Florence flask , and heat applied to the bottom hy means of a spirit lamp . In a short timethe salt Avill melt and effervesce

, , Avhen the gas will be liberated . When the flask is filled with the oxygen , a taper Avill burn very vividly in it , and even if previously bloAvn out , it will be immediately rekindled on introducing it into the flask . A piece of charcoal , Avhich can only be made to burn Avith difficulty in the air , and the light from the combustion of Avhich is of a dull red colour , scarcely visible in daylight , burns with great

splendour in oxygen ; and many metals and other substances , Avhich cannot be burned in the atmosphere Avithout the continued application of a powerful heat—iron , for example—may be made to burn readily , and Avithout requiring any heat but that Avhich results from their OAVU combustion , iu the gas . To observe this , a coil of iron wire should be used , at the end of Avhich is placed a little sulphur or other

inflammable substance . The sul p hur being lighted , and the Avire introduced into the gas , the combustion of the iron will take , place AA'ith great splendour , and sparks are tlnwn out , AA'hich are so highly heated , that by slinking the Avire in a peculiar manner , they may be made to pass completel y through the sides ofthe glass vessel Avhich contains the gas .

Besides atmospheric air , Avhich appears to be merely a mechanical mixture of the two gases , Avithout any chemical union ; oxygen and nitrogen may be combined iu four proportions , forming a series of compounds possessing very peculiar properties . These are : — 1 . Nitrous oxide , or protoxide of nitrogen , which consists of one and three quarter parts , by Aveight , of nitrogen , combined Avith one

of oxygen . 2 . Nitric oxide , deuloxide of nitrogen , or nitrous gas , Avhich contains one and three quarters part of nitrogen and two-of oxygen . 3 . Nitrous add , containing one and three quarters part of nitrogen and four of oxygen . 4-. Nitric acid , composed of one and three quarters part of nitrogen

and five of oxygen . The first named is that curious compound popularly known by the name of laughing gas . Although not fitted to support life , it may be respired , for a short time , Avhen it produces most remarkable and highly pleasurable sensations . The effects upon different persons are very various , but appear to consist generally in an involuntary and

irresistible propensity to laughter , ami to muscular action , thrilling in the extremities , a rapid flow of vivid ideas , & c . Sir H . Davy gives an account of its operation on several persons AVIIO inhaled it . The account of its effect ;* on Mr . Wedgwood is amusing . Mr . WedgAvood breathed atmospheric air at first without knowin g it AY as so . lie declared it to have no effect , Avhich confirmed him iu his disbelief of the