182 Scientific Intelligence, 



in this case must be pure, for aqua regia will remove the color in 

 either case. 



But the most delicate test of mercury is, after whitening the gold 

 of this little galvanic apparatus, to coil the strip of gold, place it in 

 the bottom of a tube, draw out the tube at the other end so as nearly 

 to close it, and then by heating the bottom expel the mercury from 

 the gold, and allow it to condense in tlie contracted part of the tube. 

 The smallest portions of mercurial salt may in this way be detect- 

 ed.— /<:?e?». 



23. On Potassium and Sodium. (Ann. de Chim. XL. 327.) — 

 M. SeruUas remarks, that a piece of potassium put upon a bath of 

 mercury, gradually amalgamates, acquiring a rotatory motion due to 

 its action upon the water in the atmosphere which evolves hydrogen. 

 In dry air, the amalgamation takes place without motion. But if 

 pieces of sodium be thrown upon mercury, they are again thrown off 

 with a small explosion, accompanied with light and heat. On the 

 other hand, potassium burns on the surface of water, whilst sodium 

 tlecomposes, without producing combustion, so that the phenomena 

 produced by the metals with the two fluids, are tlie reverse of each 

 other. 



The effects on water are of course due to the superior tempera- 

 ture acquired by the potassium, occasioning inflammation, whilst that 

 obtained by the sodium is not sufficient for the purpose ; but if a so- 

 lution of gum arable be used, not too dense nor too thin, then the 

 sodium fires, because the fragments, being retained at one point, be- 

 come sufficiently heated to ignite with a yellow flame, and then move 

 over the surface of the fluid like potassium. If sodium be fixed upon 

 a bad conductor of heat, as wood, then a drop of water will fire it ; 

 but if it be placed upon glass or porcelain, then the effect will not 

 take place ; the abstraction of heat in these cases, as well as in that 

 where a surface of pure water is used, is too rapid to allow of the 

 sufficient elevation of temperature.-— /c/ew. 



24. Test for vegetable and animal matter. (Jameson's Jour.) — ■ 

 The nitrate of silver is the test which Dr. Davy thinks to be one of 

 the best for detecting the presence of organic matter in solution. A 

 pure solution of this salt is not altered by the sun's rays ; but if the 

 minutest quantity of animal or vegetable substance be dissolved in 

 the water, the solution is discolored : with common distilled water. 



