120 SCIENTIFIC AMUSEMENTS. 



will be produced, from which crystals of nitrate of barium will 

 deposit after evaporation. 



Expt. 116. To dissolve Copper in Nitric Acid. Pour some 

 diluted nitric acid (aquafortis) on fragments of copper ; these will 

 rapidly dissolve, forming a blue solution, whilst a gas (nitric oxide) 

 is evolved with effervescence. As with the chalk, chemical change 

 takes place, so that metallic copper cannot be regained from the 

 solution by simple evaporation or cooling ; the gas now evolved is 

 different from either hydrogen or carbon dioxide, one principal 

 characteristic of it being that it forms deep red fumes when it 

 comes in contact with the air (vide Expt. 223). A saline com- 

 pound termed nitrate of copper is produced in this experiment, 

 corresponding with the chloride of calcium formed in the previous 

 one. 



Expt. 117. Another Way of dissolving Copper. Put a few 

 copper filings into a test-tube, pour over them a teaspoonful of 

 strong sulphuric acid (oil of vitriol), and heat cautiously with a 

 lamp. As the acid gets hot a chemical action begins (not per- 

 ceptible whilst the materials are cold) ; the copper gradually 

 dissolves, and effervescence takes place ; but the gas now evolved 

 (sulphur dioxide) is different from either of those obtained in 

 the last two experiments, possessing a strong smell of burning 

 brimstone. When the contents of the test-tube have cooled, pour 

 them slowly into a little water ; a great deal of heat will be pro- 

 duced, and probably some steam, owing to the action of the water 

 on the acid (Expt. 98), and a blue solution will be formed, con- 

 taining the compound sulphate of copper, corresponding with the 

 nitrate of copper formed in the last experiment. 



Caution. Be careful in mixing the sulphuric acid with water 

 after the heating is finished. Let the whole cool, and pour the acid 

 into the water, and not vice versa. Compare Expt. 98. 



The gas (sulphur dioxide) produced in this experiment in some 

 respects resembles carbon dioxide (Expt. 99) in its chemical 

 properties. If a little of it be collected in a jar by displacement, 

 holding the jar mouth upwards (as in fig. 57, and using a generator 

 like that shown in fig. 55), it will be found to extinguish a lighted 

 candle when this is lowered into the jar at the end of a wire or 

 string; by pouring a little water into the jar, and shaking it up 

 vigorously, the water will dissolve the gas, forming a solution of 

 sulphurous acid, such as that used in Expts. 135 and 164. If a 

 little solution of caustic soda be used instead of water, the soda 

 will combine with the gas (as with carbon dioxide, Expt. 143), 

 forming a compound termed sodium sulphite ; from which the gas 

 sulphur dioxide can be reproduced by treating it as directed in 



