117 



each detail carefully rehearsed ; and the workmen executed 

 their orders with a silent and unerring obedience worthy of 

 the calm and provident self-possession in which they were 

 given. 



It has been found that a good criterion of the time for 

 pouring the alloy into the mould is afforded by stirring it with 

 a pole of dry wood. This, as long as the temperature is above 

 a certain point, reduces the film of oxide which covers its 

 surface; and it becomes clean and bright, though a new film 

 forms immediately. At length as it cools this reduction no 

 longer occurs; and at a signal the three crucibles are emptied 

 into the mould by means of levers connected with the pivots 

 of their cradles. Though familiar with heavy castings, Dr. 

 Robinson had never seen any thing so magnificent as the 

 burning lake that was then produced ; and for many minutes 

 it rolled in heavy waves like those of quicksilver, which broke 

 in a surf of fire on the sides of the mould, effecting the most 

 perfect mixture of the metal. At last it became solid, and 

 was examined as it cooled, till it barely yielded to pressure 

 with an iron rod at its centre, which is the indication that it 

 may be removed to the annealing furnace. 



This furnace extends along the fourth side of the mould : 

 it is a low square chamber lined with firebrick, with sides 

 about thirty inches thick, strongly hooped, and covered by 

 an arch, from the centre of which rises a flue. Its floor is 

 convex, of the same curvature as the speculum, and is heated 

 from beneath by nine arches, which communicate with lateral 

 flues. It opens towards the mould by a low arch a little wider 

 than the speculum ; but behind has merely an aperture to ad- 

 mit an iron bar. For some weeks the chamber and arches had 

 been kept full of burning turf, so that the whole interior was 

 of a full red heat. The speculum, also red hot (at which 

 temperature, it is to be remarked, the alloy has nothing of that 

 brittleness which characterizes it when cold, but is as tough 

 as malleable iron), was cleared from the sand, and encircled by 



