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POPULAR SCIENCE REVIEW. 
manent phosphorescence is produced. The cause of this is now shown to 
he the successive decomposition and recomposition of a singular body well 
known to chemists, the compound which anhydrous sulphuric acid forms 
with nitrous acid. When in the state of vapour, and very rarefied, the 
spark separates it into its two constituents, nitrous acid and sulphuric 
acid, which have only feeble affinities for each other. When the electricity 
ceases to pass, the elements cannot coexist in the vapourous state without 
recombining, especially in the presence of oxygen ; and it is during these 
molecular evolutions that the phosphorescence is kept up. 
The action of the voltaic pile upon different substances in the state of 
igneous fusion has been examined by M. Giradin, in the laboratory of 
the Due de Luynes. Passing over the results obtained with salts of potash 
and soda, which are of no special interest, we may mention the conclu- 
sions at which he has arrived in the case of alloys. All alloys, without 
exception, lose their homogeneousness when traversed by the current. 
Thus, fused plumbers’ solder, when electrolized, becomes brittle at the 
positive pole, and soft and malleable towards the negative pole. The 
amalgams and alloys of potassium and sodium can be operated upon 
when cold. The amalgam of sodium decomposes water when taken at the 
negative pole, but not at the positive. Potassium and sodium alloy, under 
the influence of the current, solidifies at both poles. Whatever the 
electro-chemical rank of a metal, if present in small quantities in the alloy, 
it goes always to the negative pole. The amalgams of gold and bismuth 
dissolved in mercury may be taken as examples. Whatever the amal- 
gamated metal, it always returns to the negative pole. 
II. Applied Chemistry .—The manufacture of soda has lately received 
a new impetus by the discovery that a very slight additional trouble, in 
one stage of the operations, will enable a large quantity of the soda to be 
obtained in the pure caustic state ; besides effecting a great saving in 
carriage, the product is obtained in a more concentrated and available 
form. Dr. Pauli has lately shown how this crude caustic soda may be 
obtained in the perfectly pure state on the large scale. Three tons of it 
are fused in a cast-iron pot, and the scum which rises to the surface is 
ladled off ; several of the impurities are got rid of in this way. The pot 
is kept at a dull-red heat all night, and in the morning the mass appears 
perfectly transparent, the sides and bottom of the vessel being coated with 
cauliflower- shaped crystals containing all other impurities originally pre- 
sent in the soda. The clear fused liquid is ladled off from these crystals, 
and, when cold, is ready for use. The caustic soda prepared in this way 
is hard and brittle, and can be easily obtained in fine powder ; the only 
impurity which it is likely to contain being a trace of carbonate, it will 
doubtless prove a valuable reagent in manufacturing, and in chemical 
laboratories. 
The application of chemical knowledge to the preservation of food has 
not received the attention which so important a subject deserves. One of 
the most ingenious adaptations of this sort is a plan devised by Mr. M'Call, 
who adopts the old plan of expelling air by boiling, but adds an ingeni- 
ous contrivance of his own. All who have been condemned to live on 
preserved meats, are well aware that a little decomposition almost always 
