CHAP, i.] THE ART OF WARMING. 345 



as the grate is only visible through a narrow aperture, there is 

 scarcely any direct radiation from the flames or the glowing coals. 

 The draught, on the contrary, is not diminished, but the amount of 

 air passed through is relatively rather small, on which account the 

 ventilation is generally insufficient. Hygienically speaking, stoves 

 form an inferior means of warming to open fireplaces. Their forms 

 are very varied, as well as the material of which they are made. 

 Cast-iron stoves, owing to the great conductibility of the metal, are 

 very quickly heated : their sides become red-hot, and, besides the 

 insufferable heat thus caused, serious inconveniences are the re- 

 sult. One of these arises from the high temperature to which the 

 air is raised, and the consequent dryness which affects the organs of 

 respiration. This is remedied by placing a vessel of water upon the 

 stove; this, by evaporating slowly, furnishes the required moisture 

 to the air. Another inconvenience of more consequence has been 

 recently noticed. The red heat of the cast-iron causes the formation 

 of a gas, carbonic oxide, which is eminently poisonous, even when 

 mixed with the air in very small proportion. It is thought by some 

 that the glowing metal becomes permeable to the gases of combustion 

 by a process of exosmosis or of dialysis, as explained by several 

 writers, Graham, Henry St. Glair Deville, &c. ; by others it is 

 believed that the gas in question is formed at the expense of the 

 organic particles of dust which become burnt by contact with the 

 sides of the stove, or else by the decomposition by the glowing 

 metal of the carbonic acid of the atmosphere. Whatever may be the 

 cause of its formation, the phenomenon is proved, and with it the 

 unhealthiness of cast-iron stoves, whenever, at least, they are heated 

 till the sides become red-hot. 



Stoves of brick, earthenware, and fire-clay, or even metal stoves 

 which have a fire-clay lining to the grate, are without this incon- 

 venience ; but then they are heated much less quickly, on account of 

 the feeble conductivity of the material forming the covering, although 

 of course, for the very same reason, they preserve their heat much 

 longer, and their use is much more healthy than that of cast-iron 

 stoves, whose principal advantage is their being very economical. We 

 have already ,said that ventilation with stoves is much worse than 

 with open fireplaces. Their heating effect is as much greater. They 



