104 HEAT OR CALORIC. 



3. Gunpowder is safely dried, in a similar manner. 



4. By surrounding the vessels with steam, pharmaceutical extracts 

 are made, without injury to delicate principles. Chemical precip- 

 itates are sometimes dried in the same mode. 



5. Steam is employed in bleaching. Instead of boiling the stuffs 

 with solution of potash, they are steeped in that alkali, and then hung 

 up while wet, in a chamber which is afterwards filled with steam, 

 which enables the alkali to dissolve and remove the coloring matter 

 more effectually and more rapidly than in the old way.* 



6. It is applied to cookery. It is neat and effectual, and the same 

 water may in fact be used twice ; once in the boiler as water, and 

 once, as steam, in another vessel, which may be made of tinned iron, 

 and placed in any convenient situation, with which a communication 

 should be established by a bright tin tube ; the boiler must be fur- 

 nished with a lid and a safety valve. 



7. It is used for heating baths and dye vats. The steam may be 

 made to pass either through tubes, immersed in the water, or, it may 

 be thrown directly into the water, which it will heat very rapidly. 

 There should be a valve in the tube of communication to prevent the 

 reflux of the water into the boiler. 



Very large quantities of water may be thus heated in vessels of 

 wood, and in one third part of the usual time. 



8. For creating a vacuum. This is perhaps more easily done 

 by the action of steam than in any other way. The first effect 

 when the steam engine is put into operation, is to expel the air, and 

 large vessels may, in this manner, be almost instantly filled with 

 steam, which, being quickly condensed, leaves a pretty good vacuum, 

 containing little else than a feeble vapor of water. 



An ingenious still has been constructed by Mr. Barry, for making 

 vegetable extracts in vacuo ; both still and receiver are freed from 

 air, and as water will then boil at a temperature below 100, the veg- 

 etable extracts are obtained stronger and without empyreuma or de- 

 composition, f 



(V.) NATURAL OR SPONTANEOUS EVAPORATION. 



(a.) This is the gradual wasting of fluids and of some solids at 

 atmospheric temperatures. It takes place at the surface, and there- 

 fore is not attended with ebullition ; it differs not at all in principle 

 from vaporization ; it is only more gentle and never produces any 

 agitation. 



Sb.) Not only all waters, but all animals and vegetables and men, 

 the entire surface of the earth give out moisture by evaporation. 

 Place almost any thing, even ice itself, under an inverted glass which 



* Murray's Elements, 6th Edit. Vol. I, p. 237. t Ibid, p. 143. 



