244 Intelligence and Miscellaneous Articles. 



which, resting- in grooves on the top and bottom of the stove, forms a 

 chamber round it which is only connected with the external air by 

 the interstices in the grooves between the envelope and the cylinder. 



To investigate the nature of the gases which might pass from 

 the stove proper into the room, the following arrangements were 

 adopted. The gases which transpire into this chamber are aspired 

 into a meter placed at the end of a series of absorption-tubes ; 

 they deposit their carbonic acid and aqueous vapour in U-tubes, 

 some filled with pumice soaked with strong sulphuric acid, and 

 some with pieces of potash. Thus purified, they pass over oxide 

 of copper heated to redness ; the hydrogen and carbonic oxide 

 they contain are converted into aqueous vapour and carbonic acid. 

 These substances are weighed by being successively passed through 

 tared tubes, the first containing pumice impregnated with concen- 

 trated sulphuric acid, and the second potash. The gases are then 

 drawn into the meter, which sends them into the atmosphere. 



[It would seem, from an extensive Table furnished by the authors, 

 that 1000 litres of air drawn through the tubes contained, on the 

 average, about \ a litre of hydrogen and \ a litre of carbonic 

 oxide. These gases therefore pass through the sides of a cast-iron 

 stove heated to dull or to bright redness.] 



These results are readily explained if we remember the porosity of 

 iron, and the greater porosity of cast iron*. 



Graham's experiments have shown, moreover, since our own of 

 1863, that iron absorbs at a red heat 4*15 times its volume of oxide 

 of carbon when it is exposed to an atmosphere of this gas. 



The oxide of carbon absorbed on the inside of the stove dif- 

 fuses on the outside into the air ; and the effect is continuous ; 

 hence the disagreeable nature of the air in rooms heated by cast-iron 

 stoves, or by air in contact with red-hot plates. — Comptes Rendus, 

 January 13, 1868. 



ON CURVES FULFILLING THE EQUATION 



da/ 2 dy 2 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 I find that the property of multiple points in curves fulfilling the 

 above condition, demonstrated in a paper which I sent to the Royal 

 Society last year, and which appeared in their ' Proceedings ' and in 

 your Magazine, had been previously published ( a few years ago by 

 M. Haton dela Goupilliere in the Journal de T E cole Poly technique. 

 I am, Gentlemen, 



Your most obedient Servant, 



W. J. Macquorn Rankine. 



- * We have not yet found cast-iron tubes which would preserve a vacuum. 



