24 British Assodatio7i for the Advancement of Science. 



pigs made with the cold and hot blast, and that he had not found 

 any phosphorus in the specimens of cast iron whose analysis he 

 he had detailed. — Mr. Tennant stated, that the bar iron by the 

 hot blast was equally tough, both hot and cold. — Mr. Guest in- 

 quired of Mr. Tennant, whether in the puddling, hot blast iron 

 did not lose more than the cold blast iron : but to this no satisfac- 

 tory answer was given. — Dr. Clarke contended, that as the impu- 

 rities of cold blast iron are about double those of hot blast iron, 

 it was impossible that, as suggested by Mr. Guest, this latter 

 should undergo a greater waste in the process of refining. If 

 such should be proved, he would consider it a chemical miracle. 

 In continuation, Dr. Clarke observed, that manufacturers were 

 too much in the habit of working by what he called the Rule of 

 Thumb, and that, in particular, as the difference of the quantity 

 of pig iron depended materially upon the heat employed, by not 

 attending to this essential condition, iron-masters were liable to 

 fall into erroneous conclusions as to the value of any particular 

 improvement. ]\Ir. Guest being called on by the President to 

 speak to this point, stated distinctly, that he found the hot blast 

 iron to, lose more in puddling than the cold ; and he had the im- 

 pression that it was of inferior quality. — Dr. Thomson asked, 

 whether the iron referred to by Mr. Guest was, or was not, made 

 from cinder ; to which Mr. Guest replied, that in some cases it 

 was, but that his observation in reference to the greater loss ex- 

 perienced by hot blast iron in the refining surface was applicable 

 to varieties in the manufacture of which cinder was not employed. 

 — Professor Johnston expressed his surprise at the absence of 

 phosphoric acid from the GlasgoAv iron, the more especially, as in 

 the Newcastle coal-field phosphoric acid is abundant, and the 

 nodules of clay iron-stone, which may be considered as coprolites, 

 always, as is well known, include phosphoric acid. He also 

 stated, that as specimens of hot and cold iron have frequently the 

 same physical properties, it is very difficult to pronounce upon 

 the relative value of these processes. The white and black cast 

 iron also may have the very same composition, and therefore the 

 quality of iron must be referred to something totally extraneous 

 to chemical constitution. In fact, quick or slow cooling will de- 

 termine the pig to be of the one or the other color. — The President 

 observed, that, though generally speaking, black iron may be 

 considered as yielding the best malleable iron, this could not, 



