208 SCIENTIFIC AMUSEMENTS. 



union of the sulphur and the oxygen, and form a solution con- 

 taining sulphurous acid ; on dipping a blue litmus paper or other 

 test-paper indicating the presence of acids (Expt. 142) into the 

 liquid it will be reddened. Sulphurous acid solution destroys the 

 colour of many vegetable substances, especially when strong,- as it 

 exerts a bleaching action upon them. 



Expt. 239. To prepare Phosphoric Acid. Bum phosphorus 

 in a bottle of oxygen as in Expt. 234; cork the bottle and allow 

 it to stand an hour or two; at the end of this time all the white 

 fumes of oxide of phosphorus formed by the combination of phos- 

 phorus and oxygen will have subsided and become dissolved in 

 the few drops of water which will have remained adhering to the 

 glass Avhen the bottle was filled with the gas. Rinse out the 

 bottle with a teaspoonful of distilled water, and cautiously taste 

 the liquid; it will be found sour to the taste (intensely so if only 

 very little water be used), and highly acid to blue litmus and 

 other similar test-papers. 



By burning phosphorus cautiously in perfectly dry oxygen it 

 is possible to prepare "pentoxide of phosphorus" as a white 

 powdery solid ; if a little of this is brought into contact with a 

 few drops of water a hissing sound is produced and steam is formed 

 on account of the great heat developed during the combination of 

 the pentoxide of phosphorus with the water to form phosphoric 

 acid, which results as a warm concentrated solution if too much 

 water have not been used. 



Expt. 240. To Produce Heat by the Combination of Water 

 with Lime. On to a lump of good quicklime gradually sprinkle 

 water ; the lime will gradually get hot and finally crumble to pieces 

 and give off steam ; if too much water have not been added the 

 resulting " slaked " lime is a powder dry to the touch, notwith- 

 standing that it weighs considerably more than the original quick- 

 lime (3 parts of quicklime furnish nearly 4 of dry slaked lime). 



Pack a tin can holding a pint of water inside a flower pot, filling 

 up the space between with lumps of good quicklime the size of a 

 walnut. Now gradually sprinkle water on the lumps so as to 

 slake the lime ; the heat produced will warm up the water in the 

 tin can so that under favourable circumstances it can be made to 

 boil, or at least to become hot enough to scald the finger if dipped 

 in. 



In this experiment the chemical action is of the same general 

 character as in the last, viz., the combination of water with 

 something else, producing a new substance and developing 

 great heat in so doing; but the compound formed is of very 

 different nature in the two cases ; when phosphorus pentoxide is 



