388 Correspondence of J. Nickles. 
phosphorus by treating phosphate of lime with carbon and chlor- 
hydric acid.—F nally, the investigators of aluminium are giving 
themselves much labor, but still do not succeed in preparing this 
metal except at great expense. 
Dilatation and Contraction of Metallic Plates.—The imstru- 
ments for measuring dilatations of metallic plates are of great 
delicacy, giving results with very close precision. There are 
cases, however, in which a hundredth of a millimeter in differ- 
ence of length may be of value, and this is the fact with the 
standard meter, the basis of the metric decimal system. M. Sil- 
bermann, Superintendent of the Conservatory of Arts and Trades, 
has just carried the precision to 3-thousandths of a millime- 
ter. It is known that a rule suspended by one end becomes 
elongated thereby, and one standing on its end, owing to its 
weight, is shortened: and by placing the rule in a horizontal po- 
Sition again, it is supposed to take its original length. By-em- 
ploying his process, the germ of which is presented in a former 
work of this physicist,* M. Silbermann has shown that the rule 
that has been suspended retains its increased length when placed 
horizontally ; and so with the rule that has stood on itsend. ‘The 
ifference is only in thousandths of millimeters; still if it can be 
measured, this is sufficient reason why it should not be neglected. 
New Greek Fire-—The war in the east has stimulated the 
zeal of those in Europe who are interested in improving the art 
of destruction. Projects the most remarkable and curious are 
proposed. ing persuaded that one of the means of preserving 
peace to humanity consists in perfecting our methods of destroy- 
ing life, and not desiring that in this respect one nation should be 
ore favored than others, we mention here some of the projects 
which rest on serious principles. anil 
The Greek fire has at different times engaged attention with- 
out its being exactly known in what it consists. In 1755 a gold- 
smith of Paris, named Dupré, discovered an inflammable liquid 
which burned under water. Louis XV. allowed him to make ex- 
periments in the canal of Versailles, and then in different sea 
- ports, to try the power of the liquid in setting vessels on fire. It 
is said that the results produced were terrific. However the king 
believed it his duty to refuse the advantages which the invention » 
promised. He withheld Dupré from publishing his discovery; 
and gave him a pension. Dupré died and carried off his secret 
* This Journal, January and March, 1853. 
