194 ACIDS, ALKALIES, AND CLEANING 



taste and other properties of the residue show that it is 

 common salt. It is " neutral to litmus," as we should ex- 

 pect from the method by which it was made. 



If dilute nitric acid is neutralized with soda or with caustic soda, the 

 solid obtained is sodium nitrate; with dilute sulphuric acid the product 

 is sodium sulphate. If potassium carbonate or potassium hydroxide 

 were used with each of these acids, the products would be potassium 

 chloride, potassium nitrate, and potassium sulphate, respectively. Since 

 all of these substances are formed by the neutralization of an acid by a 

 basic substance, just as sodium chloride is, they are all called salts. 

 They have, in general, a salty taste, although there are decided dif- 

 ferences between the tastes. Calcium hydroxide, or carbonate, if 

 neutralized with these acids, gives calcium chloride, calcium nitrate, 

 and calcium sulphate, respectively. 



221. Tests for Certain Salts. To test for a substance, 

 as we use the word " test " in this section, is to find out 

 whether the substance in question is present or not. We 

 find this by the behavior of whatever is being tested. 

 Thus we can show that a solution contains an acid by 

 using the litmus test, and by the behavior of the solution 

 with metals, carbonates, etc. (cf. 214 to 217). Still, 

 these tests will not distinguish sulphuric acid from many 

 other acids. But if we apply the test for sulphates, in addi- 

 tion to the other tests, then there can be no doubt. Tests 

 " work " because no two substances behave exactly alike, 

 or have exactly the same properties (cf. 5). 



In testing for a salt we ask ourselves two distinct ques- 

 tions : 



(1) What metal does it contain? 



(2) To what acid is it related; that is, is it a sulphate, a 

 chloride, or what? 



