98 Chemistry. [Lecture 27. 



pure distilled water, which produces no white- 

 ness at all. 



3. The influence or energy of this attraction 

 reaches to a distance so small as to be imper- 

 ceptible to our senses, as it does not appear to 

 act till the bodies are in contact. Of this there 

 is an instance in the difficulty of applying the 

 particles of sulphur and mercury sufficiently 

 near to make them unite. In this respect che- 

 mical attraction is analogous to the attraction of 

 cohesion. For if two pieces of lead are pressed 

 strongly together with a twisting motion, so as 

 to bring them into violent contact, they take 

 hold of one another almost as firmly as if united 

 by fusion. 



From these observations we shall understand 

 some of the principal laws of mixture and solu- 

 tion. 



I. When we desire to make two bodies act 

 upon one another, it is necessary that one or 

 both of them should be fluid, or rendered fluid, 

 or disposed to fluidity, immediately after mixing. 

 This rule is applied to salts in particular, 

 " which do not act unless in solution." To il- 

 lustrate this by experiment : 



First. To crude muriate of ammonia in pow- 

 der (which is a compound of ammonia or vola- 

 tile alkali and muriatic acid, which has a strong 

 attraction for it, and depresses its volatility) I 

 add another salt in powder, which has a greater 



