Miscellanies. 363 
bon, and as it issues from the tube burns with a flame which emits 
but little light. 
he time necessary for the completion of the process depends on 
the dimensions of the bars of iron and the temperature to which they 
are subjected. When the tube is of a red brown color and the bars 
are two inches wide and six lines thick, eighteen or twenty hours 
are sufficient for the cementation. The iron may be very easily 
surcharged with carbon. I have seen thin bars which were almost 
in the state of graphite (plumbago). ‘Trial bars placed in the dises 
which close the tube indicated the progress of the cementation and 
the moment when the operation should be stopped. 
The steel, when taken from the tube, is covered with little blis- 
ters exactly like those made by the common methods. I have not 
seen the apparatus in operation and can give no details relative to 
the manner of conducting it; neither do I possess any statements of 
its economy. M. Macintosh, from whom I have the few details 
that have been mentioned, is satisfied that the process may with res- 
pect to expense, come into competition with the usual mode of ce- 
mentation. He considers the stee] obtained by the hydrogen gas as 
more homogeneous and of a superior quality to the ordinary. He 
has manufactured several tons in this mode in order to demonstrate 
the reality of his discovery for which he has obtained a patent. 
All the steel fabricated by M. Macintosh has been sold and used, 
the greatest part converted into cast steel and employed in the man- 
ufacture of fine cutlery and the preparation of instruments which re- 
quire steel of the first quality —Annales des mines, tome v. 171. 
14. J. G. Determination of the Mathematical Law by which the 
elastic force of Aqueous Vapor increases with the temperature ; by 
M. Rocue, Professor of Mathematics and Physics in the School of 
Marine Artillery, at Toulon. Extracted from the Recueil Indus- 
triel, for Mars, 1829.—It has been ascertained, Ist that a moder- 
ate increase of temperature, greatly increases the elastic force of 
steam; 2d that this force increases nearly in geometrical progres- 
sion for every 30° of Fabhrenheit,—the elastic force doubling suc- 
cessively for every successive augmentation of 30° from the boiling 
point. 
The experiments however, both of French and English philoso- 
phers prove that the tension of steam at high temperatures varies 
very sensibly from this law, and various empirical formule have been 
