26 LESSONS ON CHEJinSTRY. 



that the kind of cabbage used to prepare pickles (red cab- 

 bage), which when growing in the garden is of a violet 

 colour, becomes of a bright red when placed in vinegar. If 

 you were to pour upon the cabbage leaves water mixed with 

 a few drops of vitriol, or spirits of salts, precisely the same 

 change of colooi' would be produced. Now substances which, 

 like vinegar, vitriol, and spirits of salts, possess a sour taste, 

 and alter the violet colour of cabbage leaves to a red, are 

 termed acids by chemists ; and strips of paper coloured by 

 being dipped in liquids procured by boiling in water the 

 leaves of the red cabbage, the common violet, or a certain 

 blue vegetable colouring matter called litmus, are employed 

 by them in their experiments, for the purpose of testing or 

 ascertaining the presence of these substances. 



12. When common potash, or the soda ash employed in 

 bleaching, is dissolved in water, and tested by means of the 

 prepared papers just described, the colour of the paper is not 

 changed to red. On the contrary, if the paper be reddened 

 by the action of an acid, and afterwards dipped in the solu- 

 tions, its original blue colour wUl be restored.* To sub- 

 stances which like potash and soda ash possess a peculiar 

 acrid, disagreeable taste, and restore the blue colour to red- 

 dened test-papers, chemists give the name of alkalies. 



13. When acids and alkalies are mixed together in proper 

 proportions, they enter into chemical combination^ and form 

 what are termed neutral compounds, in which neither acid 

 nor alkaline characters can be detected. Thus the taste of 

 vitriol, (sulphuric acid) is intensely sour, but if we gradually 

 add to it potash, which is an alkaline substance, we can procure 

 a compound in which neither by the taste nor the test-paper 

 can we detect the characters which distinguished these sub- 

 stances before their union, f Such compounds of acids and 

 alkalies are very numerous, and are designated salts by 

 chemists, and receive a name derived from the ingredients 



* When the blue liquid, obtained by steeping or boiling red cabbage 

 or violets in water, is mixed with an alkaline liquid, as a solution of 

 potash, soda ash, or ammonia, its colour is changed to green. 



f The teacher may impress the nature of the change which is 

 effected by chemical combmation, upon the minds of his pupils bj- 

 illustrating the properties of sulphuric acid and soda (soda ash) in 

 their separate state, and as united in sulphate of soda (glauber salt), 

 which compound exhibits no trace of the acid and alkaline characters of 

 its constituents. 



