248 ON THE CONSTRUCTION AND HEATING OF HOT-HOUSES. 
plete, Mr. Witty, civil engineer, constructed a peculiar furnace (figure 6), for which he 
obtained a patent ; Messrs Chanter and Co. purchased the patent right, and made 
several important improvements ; and as such it appeared in our Magazine of 
Botany i vol. 1, page 133, It is now _ 
further improved by the box and screw 
being removed, &c., and from what we 
have seen of its action by two furnaces 
erected at Chatsworth, we apprehend it 
will answer admirably ; but of these 
we shall speak at a future time more 
fully. 
It will be seen in our previous description, vol. 1, page 133, that these furnaces 
are constructed so as to divide the consumption of coal into two distinct processes, 
viz., carbonisation and combustion. For this purpose there is a retort, and carbonis- 
ing plate or distilling plane, added to the furnace grate and clinker door ; so that 
the coals are first submitted to dry distillation, and then to combustion, the gas and 
coke being burnt together, and thus prepared before they reach the bars ; thereby 
availing itself of the essential principles of combustion;, by separating the gas from 
