POTASSIUM AND SODIUM:. 



211 



vinegar. There will be an effervescence, 

 because the acetic acid expels the car- 

 bonic anhydride and forms potassium ace- 

 tate. As the gas fills the tumbler it will 

 extinguish a burning taper introduced 

 into it. 



290. Saleratus. This is the bicarbonate 

 of potash, or, strictly speaking, hydro- 

 potassium carbonate, KHCO 2 , containing 



precisely twice as much carbonic acid as the common car- 

 bonate. It is formed by passing carbonic anhydride through 

 a cold solution of potassium carbonate, and then evapo- 

 rating the solution. On heating the hydro-potassium car- 

 bonate, the extra amount of carbonic acid may be driven 

 off. It therefore loses some of its carbonic acid if it be dis- 

 solved in hot" water ; or, rather, some of it is converted into 

 the carbonate, and you have in the solution a mixture of 

 the two salts. The amount of carbonic anhydride in this 

 salt makes it useful in raising bread and cake. The acid 

 which is employed with it takes the potash to itself, and 

 sets free the gas, which by its expansive force puffs out the 

 dough, forming in it innumerable air-cells, and thus makes 

 it " light." The acid which is in sour milk is as good as 

 any other for this purpose. 



291. Potassium Nitrate, or Saltpetre. This salt, also called 

 nitre, is of special interest to us as being one of the ingre- 

 dients of gunpowder. It is a natural product in some soils 

 in hot climates, as in India and South America. The man- 

 ufacture of potassium nitrate is a curious chemical process. 

 First a calcium nitrate is produced in the following manner: 

 Animal substances, flesh, hides, etc., are mixed with lime 

 and earth, and this mixture is moistened and left to putrefy. 

 Ammonia results, the elements of which, nitrogen and hy- 

 drogen, unite with the oxygen of the air to form two things 



