Miscellanies. 363 
bon, and as it issues from the tube burns with a flame which emits 
but little light. 
_ The 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 mches 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 steel 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 manes, 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 Fahrenheit,—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 
ih) 
