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only measurable drawings of this kind which are really useful in 

 practice. In criticising his writings it may perhaps be said that his 

 dread of mere empiricism and his intolerance of inaccuracy often led 

 him to magnify points which now seem to be somewhat trivial, and he 

 sometimes withholds the expression of his own opinion when the reader 

 has fairly a right to expect his guidance and would be grateful for 

 the support of his authority. 



Of all his work that relating to iron and steel is perhaps the most 

 important, and it began early in his metallurgical career with an 

 elaborate piece of analytical work. The first International Exhibition, 

 of 1851, contained a very extensive and highly interesting series of 

 British iron ores, collected with great labour and at considerable ex- 

 pense by Dr. Percy's friend, Mr. H. S. Bakewell, of Dudley, and after- 

 wards presented by him to the Geological Museum in Jermyn-street. 

 Mr. Bakewell placed at Dr. Percy's disposal the sum of £500 towards 

 defraying the cost of analysing the more important of these ores. The 

 work was completed by Dr. Percy with but slender aid from Govern- 

 ment, and the results are embodied in his treatise on Iron and Steel, 

 which was published in 1864. They have rightly been described as 

 the first serious attempt at a survey of our national resources as 

 regards ores of iron. With regard to the actual extraction of iron 

 from its ores, his services were not less important. In 1855 the fact 

 was established that pig iron from the blast furnace contains the 

 greater part of the phosphorus originally present in the ore. Dr. 

 Percy pointed out that phosphorus is not eliminated to a sensible 

 degree in the Bessemer process, as it is in the old process of puddling ; 

 and he was of opinion that if the Bessemer process was to be 

 " generally applicable in this country, it must be supplemented by the 

 discovery of a method of producing pig iron sensibly free from 

 phosphorus and sulphur with the fuel and ores which are now so ex- 

 tensively employed in our blast furnaces." The practical solution of 

 the problem of eliminating phosphorus in the Bessemer converter, 

 and the wide adoption of a process of truly national importance, are 

 the outcome of Dr. Percy's teaching, for the problem was solved by 

 three of his pupils. The delivery of his eloquent address in 1886, as 

 President of the Iron and Steel Institute, fittingly ended the active 

 portion of his labours with regard to these metals. 



His most noteworthy addition to practical metallurgical processes 

 was described in a paper written by him in 1848, and published in 

 the same year in a journal called ' The Chemist.' A translation of 

 this paper reached a distinguished Austrian, who introduced, at 

 Joachimsthal, the process now known as that of von Patera, which 

 depends on the solubility of chloride of silver in hyposulphite of soda. 

 Early in 1884 this process was modified in America, by Mr. E. H. 

 Russell, in order to render it applicable to ores poor in silver, which 



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