258 METALS. 



643. But this rule is not without ex- 



Do impurities 



always pro- ception. Certain substances seem to in- 

 crease the action. It is therefore always 

 prudent where it is proposed to conduct water through 

 leaden pipes, to ascertain by direct experiment, whether 

 the particular water in question acts upon the lead or 

 not. 



644. ILLUSTRATION. The difference in 



Describe the . 



experiment the action of pure water upon lead, and 

 ithlead and that which contains foreign substances in 



distil Lea water. 



solution, may be readily proved by exper- 

 iment. For this purpose, bright slips of lead may be 

 placed in two tumblers, the one containing rain water, 

 and the other well or spring water. The former will 

 soon become turbid while the latter remains unaffected. 



645. The presence of lead in the former 



How may the 



presence of case may be still more strikingly shown, 

 fawn*/ ^ eUeT ky adding to the water a few drops of a 

 solution of hydrosulpluric acid. The for- 

 mation of a dark cloud will show the presence of lead, 

 and indicate the danger to be apprehended. 



646. LEAD TREE. Dissolve some crys- 



Describe the 



lead tree and tals of sugar of lead, in thirty or forty 



Us" production. timeS theif bulk f Wat6r > and fil1 a vial 



with the solution. A strip of zinc, hung 

 in the vial, will branch out in a beautiful ar- 

 borescence of metallic lead. It may be neces- 

 sary to clarify the solution by the addition of 

 a little clear vinegar or acetic acid. A day or 

 two will be required for the completion of 

 the experiment. The effect depends on the 



