HEAT. 153 



Many colors are better and more economically prepared 

 by steam than by fire. Vegetable extracts for medi- 

 cinal purposes are best prepared by the heat of steam. 

 For heating baths, steam is far cheaper than fire. Large 

 or small apartments may be warmed by steam with clean- 

 liness andj great safety. All the culinary operations of 

 boiling are better performed by steam than in any other 

 way. In order to heat a liquid by steam, the vessel con- 

 taining the liquid, should be placed in a larger one, 

 making the open space between them steam tight, and the 

 steam admitted into this space will raise 20 gallons of 

 water at 5'2, to 212 in eleven minutes. 



One gallon of water made into steam will heat six 

 gallons at 50 to the boiling point, or eighteen gallons 

 from 50 to 100. 



It has been found that in warming large buildings, such 

 as manufactories, one cubic foot of the boiler will heat 2000 

 cubic feet of space to 70 or 80 ; and that one square 

 foot of surface of a steam pipe, will heat two hundred 

 cubic feet of space. Cast-iron pipes are considered the 

 best for heating apartments by steam, and should be 

 covered with lampblack and placed near the floor, as the 

 coldest air is always lowest. 



Animal food is considered more nutritious and easier 

 to digest, when prepared with steam, than when cooked in 

 the usual method. 



Evaporation. When a liquid gradually assumes the 

 form of an elastic vapor at all temperatures, it is said to 

 evaporate ; and as the temperature is increased, the eva- 

 poration is also increased. Likewise, as the pressure is 

 diminished, the evaporation is increased. 



The reason of evaporation is beautifully explained by 

 the doctrine of latent heat. We have explained how 

 liquids, in order to be converted into steam or vapor, 

 require a large quantity of heat, which combines with 

 them and becomes latent, and taking away this heat pro- 

 duces cold. 



Experiment. Place a watch glass with a small quantity 

 of ether in it, in another glass containing a small quantity of 

 water, and place them both under the receiver of an 

 air-pump. Exhaust the receiver, and in a short time the 

 ether will have disappeared, and the water will be frozen. 

 , TOL. i. NO. vi. 14* 



