76 PHENOMENA OF HEAT AND SOUND. 



works, and a discussion of some of these will close this 

 account of Aristotle's description of the phenomena of heat. 



It seems to have been usual for people living near the 

 Black Sea to encamp on the ice, for the purpose of fishing, 

 and to secure their tent poles in holes made in the ice. In 

 order to make the poles very secure, Aristotle says that they 

 poured hot water round the lower parts of the poles, and 

 that the ice formed by the rapid freezing of the water was a 

 substitute for lead.* He also says that it was a common 

 custom for some people, when they wished to freeze water 

 quickly, to expose it first to the heat of the sun.t 



Aristotle describes the manufacture of pearl-ash by the 

 Umbrians, who burnt plants, boiled the resulting ash in water, 

 and finally cooled down to crystallize the salts produced. 1 



In Meteorol. iv. c. 6, s. 7, Aristotle refers to the distortion 

 of articles of potters' clay, if these articles, hardened by cold 

 or frozen, are placed in the oven. He explains the distortion 

 by saying that there is a temporary softening of the clay by 

 the action of the water resulting from the thawing during 

 the first stage of the baking process. 



Aristotle gives a short account of the production of steel. 

 " Worked iron," he says, can be heated so as to be liques- 

 cent, and then can be solidified again, and, in this way, 

 they make steel, for the slag falls down beneath and is 

 cleared off. When this process has been carried out many 

 times, and the metal has become pure, steel is produced. § 



The " worked iron," which might at first sight be taken 

 to be wrought iron, can scarcely be this metal, because 

 Aristotle's description shows that the " worked iron " was 

 comparatively easily fusible, whereas wrought iron is not so. 

 He says, in fact, in an earlier passage, || that iron can be 

 melted only by a very intense heat, but it can be softened. 

 Here he evidently refers to wrought iron, or, perhaps more 

 correctly, a steely iron. The " worked iron " was probably 

 a crude steely iron, containing manganese, such as could be 

 obtained from the manganiferous iron ores of Greece, by 

 the ancient process of extraction by means of carbon. 

 Unfortunately, Aristotle does not describe the method of 

 extraction. The method of making steel, described by him, 

 consisted in repeatedly heating the crude steely iron, each 

 heating resulting in an elimination of some of the im- 



^= Meteorol. i. c. 12, s. 18. | Ibid. 



I Ibid. ii. c. 3, ss. 42 and 43. § Ibid. iv. c. 6, s. 9, 



II Ibid. iv. c. 6, s. 8. 



