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as well as light, is one which demands our strictest atten- 
tion. The heating value of gas is even greater than that 
of coal, and its application to domestic purposes easy and 
economical. The separation from it of ammonia by the 
processes just now alluded to, the removal of naphtha 
vapour and bisulphide of carbon, which are the chief causes 
of the unpleasant odour of gas, and the application of all 
these products to economic purposes, render the gas free 
from all the objections to which, if used in large quantities, 
it would otherwise be liable. Its advantages, too, are mani- 
fest ; the absence of all smoke, and, if properly ventilated, 
of all deposit of soot, the cheerful brilliancy of its flame, 
the facility with which the supply can be regulated, and 
the temperature consequently decreased or elevated, all 
combine to render the use of gas as a substitute for coal 
in domestic, as well as in manufacturing establishments, at 
once practicable and beneficial. 
Mr. Appold, the talented inventor of the centrifugal pump, 
at his residence, near London, has erected a small gas manu- 
factory in one of his outbuildings, and uses its products for 
every heating purpose throughout his entire premises; and 
by introducing the gas through a number of small orifices at 
the back of the grates, he obtains a cheerful and exceedingly 
warm fire. I may mention that, among other ingenious ex- 
periments he has provided each supply pipe with a throttle 
valve, so delicately suspended as to be opened or closed by 
the fall or rise of a thermometer placed on the stairs 
leading to the drawing room ; and so admirably can the 
temperature of the house thus be regulated, that he has 
assured a friend of mine that it does not vary more than 
3° or 4° during the whole year. The opening of a window 
in one of the bedrooms in a few minutes produces a fall 
in the central thermometer, which opening the supply valve 
and admitting a larger quantity of gas, causes an imme- 
