172 SCIENTIFIC AMUSEMENTS. 



nitrogen under water in a bucket or large basin, and tilting it so that 

 the gas gradually escapes, holding over it the second jar filled with 

 water, so as to collect the escaping gas. Now add sufficient oxygen 

 from another jar containing that gas to fill up the remaining fifth 

 of the jar; the two gases will rapidly intermix by diffusion 

 (Chapter IX.), and ordinary atmospheric air will result, as may be 

 tested by introducing a lighted candle, which will burn just the 

 same in the jar as in another similar one filled with ordinary air. 



Expt. 187. To prepare Laughing Gas (Nitrous Oxide). 

 When nitric acid and ammonia in solution are brought together 

 they combine, forming a neutral salt, nitrate of ammonium, just as 

 sulphuric acid and ammonia form sulphate of ammonium (Expt. 

 138). If this solution be evaporated, and the residual salt heated 

 till all water is driven off, the pure nitrate of ammonium is left as a 

 fused liquid which sets to a crystalline solid mass on cooling. If, 

 however, the heat be continued, the substance decomposes, some- 

 what as nitrite of ammonium splits up (Expt. 183) ; but with this 

 difference, that steam and the gas nitrous oxide are formed instead 

 of steam and nitrogen. The nitrate of ammonium is, like nitrite 

 of ammonium, a ternary compound of nitrogen, hydrogen, and 

 oxygen, but contains more oxygen; the result of which is that, 

 instead of nitrogen being produced, a compound of nitrogen with 

 the surplus oxygen present is formed. 



Nitrous oxide dissolves somewhat readily in cold water, conse- 

 quently it should be collected at the pneumatic trough over water 

 as hot as the hands can possibly bear. 



Expt. 188. Nitrous Oxide supports Combustion. Into a jar of 

 nitrous oxide introduce a lighted candle ; the candle will burn freely, 

 even better than in air. Similarly a 

 bit of sulphur will burn vigorously in the 

 gas if introduced by means of a " deflagra- 

 ting spoon "( fig. 79); the reason for this 

 is that the heat of the burning substance 

 introduced splits up the nitrous oxide 

 into nitrogen and oxygen, and the latter 

 keeps the material alight, just as air 

 would do, and even better. A glowing 

 spill of wood will generally burst into 

 flame when placed in a jar of nitrous 

 Fig. 79. Burning Phos- oxide, iust as it would in oxygen (Expt. 

 phorus in Nitrous Oxide. ' 



When breathed, however, nitrous oxide behaves very differently 

 from air or oxygen ; great excitement and exhilaration is first 

 brought about, which often produces laughing (whence the name 



