128 Chemistry. [Lecture 29. 



Those that have the greatest attraction for water 

 require least for their solution : some of them 

 possess so great an attraction for water, as to 

 absorb it from the air. These are called deli- 

 quescent. 



The first phenomenon in the mixture of salts 

 with water is the .separation of air from the 

 water by a seemingly elective attraction. This 

 appears by a muddiness which proceeds through 

 all the parts of the fluid, and is occasioned by a 

 number of little bubbles, which rise to the top 

 so as to form a scum ; when all these are risen, 

 the water becomes transparent. This deserves 

 to be taken notice of, as many have been de- 

 ceived by it, especially those who have written 

 on mineral waters. They often mention effer- 

 vescence in them, where there was none, and 

 the appearance of it was nothing more than the 

 air escaping. 



Another phenomenon is the alteration in the 

 heat of the mixture. In some cases it becomes 

 colder, in others hotter. When heat has been 

 produced, it has been thought owing to the vio- 

 lent attraction between the salt and water; for 

 the production of cold there has been no theory 

 offered but that of latent heat, as stated in a pre- 

 ceding lecture. 



Another phenomenon is, that if we add more 

 and more salt to the water, it will be more and 

 more slowly dissolved, and after a certain quan~ 



