280 



On Chemical Tests. 



[Oct. 



lxi. It may lastly be mentioned, to prevent misconception by the 

 young beginner, that in all cases, except where otherwise specified, the 

 test, and the substance tested, is to be in the state of solution. And 

 that, where neutralization is mentioned, he will remember that acids 

 are neutralized by alkalies, and alkalies by acids. When a solution 

 is neutralized it affects neither blue, nor leddened litmus papers; 

 i. e. the solution, so neutralized, does not change the colour of either. 

 Some neutral salts however affect litmus paper. See, Nos. 77 in the 

 subsequent list of test. 



lxit. H5f It will be highly conducive to improvement, and to the 

 acquisition of the most useful knowledge relative to the action of tests 

 if the young experimentalist exercise himself in the examination of 

 easy compounds made up by him of known combinations : for instance, 

 let him mix a little common salt, and saltpetre together in solution, and 

 test them for the bases, potash and soda; and for the acids muriatic, and 

 nitric. Let him refer to those four articles in the list of tests, and 

 endeavour, from the directions given, to ascertain both the bases, 

 and the acids to his own satisfaction, and beyond doubt. He will learn 

 more by this one experiment than by pages of printed directions not re- 

 duced to practice. Of course he is supposed to understand the modern 

 nomenclature, and to be aware that common salt is muriate of soda; 

 and that saltpetre is nitrate of potash : or, in other words, that com- 

 mon saltis muriatic acid in combination vith scda, and that saltpetre is 

 nitric acid in combination with potash. From this experiment he may 

 proceed to others ; and after he has attained some facility and skill, he may 

 examine other combinations making them more complex and difficult, 

 in proportion as his knowledge increases, and as he obtains more confi- 

 dence and dexterity in qualitative examinations. 



OBSERVATIONS ON THE BLOW PIPE. 



lxiii. So also with regard to the use of the blow pipe, practice is the 

 only efficient teacher : and the unpractised experimentalist should ini- 

 tiate himself by operating first on small fragments of known minerals 

 and metals. A few concise observations here follow with respect to 

 the examination of minerals. 



lxiv. Take a minute chip of the mineral, and place it in a hollow made 

 in a piece of well burned, hard, charcoal. Apply the blow-pipe, at first 

 at the extremity of the flame where there is the leas^ heat, and after- 

 wards gradually at the point of the blue flame where there is the great- 

 est heat. Observe the phenomena that occur, such as phosphorescence 



