14-8 Chemistry. [Lecture 29. 



plain they have a disposition to solidity, and that 

 the reason of their fluidity is their strong attrac- 

 tion for water, and the great difficulty of sepa- 

 rating it from them. 



The sulphuric acid has been crystallized by a 

 great degree of cold. The regular crystallization 

 depends on a certain degree of strength, T78 

 specific gravity, and is favoured by the mixture 

 of another acid, as the muriatic or nitric. It 

 shoots into fine crystals in this case, in a tem- 

 perature several degrees above the freezing 

 point. 



The nitric acid is always congealed into a 

 number of spiculae at four degrees below Fahr. 

 We have no account of the congelation of the 

 muriatic acid ; but it is highly probable that it 

 would also congeal. 



Another general property of these acids is, that 

 they change the colour of blue and purple vege- 

 table substances into a bright red; and this they 

 do, though the infusion has been changed into 

 green by an alkali. If the change has been recently 

 produced by an acid, the infusion may again be 

 made green by an alkali, and so on alternately. 

 It is common to deepen the colour of conserve 

 of roses by adding a little acid, by which the con- 

 serve appears richer than it usually is. 



A further property is, they readily unite with 

 alkalies, and when the alkali is what is called 

 mild (that is, in the state of a carbonat, or com- 

 bined with carbonic acid) produce great effer- 



