148 PRACTICAL LESSONS IN SCIENCE. 



still in solution. In refining the niter it is dissolved in boiling 

 water, filtered, then allowed to cool and crystallize while kept in 

 constant motion, so that the salt may be deposited in smaller 

 crystals than if allowed to crystallize from a quiet liquid. The 

 crystals are thoroughly washed, then dried for use. 



These operations illustrate some curious and interesting prop- 

 erties of the substances spoken of, and how these properties have 

 been studied out and made use of in preparing the substances for 

 use, and in most cases they were discovered and utilized by non- 

 scientific men, under pressure of business competition long before 

 they were even partially explained by a scientific man. 



Potassium nitrate is a crystalline salt that readily dissolves 

 in water, having a cooling saline taste, and strong antiseptic 

 powers, so that it is often used in preserving meats. Potassium 

 forms an interesting compound with chlorine, called potassium 

 chloride, formula KC1, which occurs in great masses in the salt 

 mines in Saxony, and is an important source of potassium and 

 its compounds. It resembles rock salt in appearance. Another 

 important salt of potassium is potassium chlorate, formula 

 KC10 3 . It is prepared by passing chlorine gas through a solu- 

 tion of potassium carbonate. As this salt gives up its oxygen 

 freely to other bodies, it is called an oxidizing agent. 



Pulverize carefully a small piece of potassium chlorate and mix 

 with it an equal bulk of sugar ; put the mixture on a brick in the 

 open air, then let a drop of sulphuric acid fall on it and a vivid 

 combustion will follow. Care should be taken both in pulverizing 

 and mixing not to use percussion or heavy pressure, and small 

 quantities should be used at least until one is familiar with the 

 explosive powers of this salt. Cream of tartar, much used in 

 cooking, is potassium tartrate, mainly obtained from fermenting 

 grape juice. 



Potassium as a metal is of no economic value, but some of its 

 compounds are among the most important known. The use 

 of the carbonate as an alkali in making soap, the use of the 

 chlorate as an oxidizing agent in the manufacture of matches, 

 and the use of the nitrate as an oxidizing agent in the manufac- 



