140 
Iron. 
quantity of materials consumed, and in the quality and 
quantity of metal produced* 
It has been already demonstrated, that the air in winter, 
by containing less moisture, is more proper for combus- 
tion. and more calculated to produce carbonated crude 
iron, than the air existing at any other season* From 
this superior quality the manufacturer obtains advantages, 
which induce him to wish for a continuance of cool air 
e * 
throughout the whole year. These effects are not, how- 
ever, uniform ; they depend greatly upon a light or heavy 
atmosphere. The keener and more still the air, the more 
rapid the combustion. During a severe frost, the de- 
scent of the materials is facilitated from one tenth to one 
fifteenth more than in rainy or hazy weather, and at the 
same time the quality of the iron is rather improved than 
impaired. When a change from frost to snow or rain 
takes place, the effects frequently become almost imme- 
diately obvious : the colour of the flame at the furnace 
head is changed ; the tuyere of the furnace inflames, and 
burns with great violence ; the lava, as it flows from the 
notch of the dam-stone, becomes lengthened and tena- 
cious ; the form of it is changed, and the colour under- 
goes the most visible alterations ; the iron no longer re- 
tains its complete saturation of carbon, but flows out 
sensibly impaired of its fluidity, and, when cold, the pri- 
vation of carbon is most evident by the examination of 
its fracture. 
When such consequences arise from the transition so 
frequent in winter from frost to thaw, it will be easily con- 
ceived that the change effected during the milder and 
warmer months must produce proportionally additional 
effects. The increase of temperature by taking up, and 
holding in solution, a much greater portion of aqueous 
vapour, will account for the ordinary effects which are an- 
nually observable in every work, Where these pernicious 
