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 the contracted part of the tube. 
The smallest portions of mercurial salt_ may in this way be detect- 
ed.—Idem. 
23. On Potassium and Sodium. (Ann. de Chim. XL. 327.)— 
M. Serullas 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 
decomposes, without producing combustion, so that the phenomena 
produced by the metals with the two fluids, are the 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 arabic 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 5 
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 
cient elevation of temperature.—Idem. 
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, 
