CHAPTER XXVI. 

 SALTS. 



78. PREPARATION OF SALTS. 



IT has been found that certain substances acids turn litmus red 

 while others turn reddened litmus blue. It will be interesting to investi- 

 gate the effect of adding these two classes of substances to one another 

 in the presence of litmus. 



i. Preparation of salts. (a) Sodium chloride. Make a solution of 

 sodium hydrate, as in Expt. 71 ii., or by dissolving caustic soda in water. 

 To a portion of the solution in an evaporating basin add dilute hydrochloric 

 acid, drop by drop, until the solution has no effect upon either a red or blue 

 litmus paper. The solution is then said to be neutral. Gently evaporate 

 the solution on a sand-bath until a dry white residue is left. Then, by 

 tasting the solid, satisfy yourself that it is common salt, or sodium chloride. 



(b) Magnesium sulphate. Take about 10 c.c. of dilute sulphuric acid in 

 a basin, and warm gently. Then add, in the presence of litmus, small 

 quantities of magnesium oxide, till the litmus is changed in colour. 

 Evaporate to half the bulk and place on one side. After a time crystals 

 are formed which may be recognised as Epsom salts. 



Acids. Hydrochloric, sulphuric and nitric acids have now been 

 studied, and it is necessary here to consider what characters these 

 three compounds, so dissimilar in many of their properties, have in 

 common, which leads chemists to call them all acids. The experiments 

 described from time to time have shown that the three compounds 

 all have a sour taste, and that they all possess the power of turning 

 a blue litmus paper red. These two properties are possessed by almost 

 all acids. In addition, moreover, all acids contain hydrogen, which 

 can, in suitable circumstances, be replaced by a metal. The metal 

 may itself turn out the hydrogen by acting on the acid directly. An 

 example of this is afforded by the preparation of hydrogen by acting 

 on sulphuric acid with /inc. Or, the hydrogen of the acid may be 

 replaced by the metal in a compound like caustic soda (sodium hydrate),. 



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