Xl PEOCEEDEN'GS OF THE GEOLOGICAL SOCIETY. 



ignited with, nitre, the resulting oxide washed and reduced, at the 

 same time that the fusion of the alloying metals was effected. 



After a few years, owing to his many engagements and the 

 pressure of what he considered his more legitimate work, he ceased 

 to apply himself so diligently to the German-silver business, and it 

 was then most energetically taken up by the Biraiingham firm, 

 Evans and Askin, who have ever since retained it almost exclu- 

 sively in their hands. 



It was about this time that he was much engaged in mining- 

 pursuits, and was consulted upon, and visited professionally, nearly 

 all the mining-districts in England and Wales, as well as many 

 important ones abroad. He was the fii^st to introduce in Corn- 

 wall the German shaking and washing table, with modifications 

 of his own. Eesiding during a part of the year at Ward 

 Cottage, beautifully situated on the banks of the Tamar, he was 

 able to make frequent visits to the interesting although short- 

 lived mines of the district of Callington, and to those of Calstock 

 and Beer Alston. He will always be remembered throughout the 

 mining-districts for his great kindness and consideration towards 

 the miners, whose social condition it was his constant aim to im- 

 prove. At great expense to himself he erected schools &c. in the 

 neighbourhood of the mines, and took an active part in their super- 

 vision. He also used his utmost endeavours to alleviate the toil of 

 the miners in ascending and descending mines : with this view, as 

 well as for the improvement of the ventilation, he, at the Tamar 

 mines, made the experiment of a sloping gallery, which ran for a 

 considerable distance under the river, by which means the miners 

 could walk up and down without the use of ladders. 



Amongst his many minor chemical discoveries may be mentioned 

 several pottery colours, amongst them the rose-pink, at a time 

 when that colour was much wanted in the potteries, the manufac- 

 ture of which he carried on for many years, at the same time as 

 " oxide of uranium," a valuable colour much used in glass-making, 

 of which he always maintained the monopoly. 



Mr. Johnson alloyed, melted, and assayed the trial-plate of the 

 Pyx, which is the criterion of the quality of the coin of this country, 

 and which is still kept in the Lord Chancellor's office. 



His greatest success, however, and that which has proved the 

 most valuable to the progress of chemistry and manufacture gene- 

 rally, was the treatment of platinum. To him undoubtedly belongs 

 the credit of having been the first after Dr. WoUaston who success- 

 fully refined and manufactured that metal upon a commercial scale, 

 and introduced it for many of the valuable purposes to which it is 

 specially adapted. The first large and perfect sheet of pure platinum 

 ever produced was made by Mr. Johnson at 79 Hatton Garden ; and 

 seeing the immense importance of this metal, he ever afterwards 

 made it his speciality. 



As narrated by Percival Johnson, it is an interesting and perhaps 

 not well-known fact that the discovery of the mode of refining 

 and consolidating platinum was disputed with Hr WoUaston by 



