270 PETER SPENCE 



cooling this rabble so as to prevent its 

 destruction. 



The " Henderson " process excelled all his 

 attempts to treat copper ores by the wet way, 

 but his automatic calciners are still, in vitriol 

 making, in use in certain districts, where 

 " smalls " are plentiful. 



The discovery of immense quantities of 

 phosphate of alumina and iron in the West 

 Indies, on the Island of Redonda, aroused 

 him to seek to discover a method of utilising 

 this mineral, so as to produce alum from the 

 alumina, and use the phosphoric acid in the 

 manufacture of manures. He patented five 

 processes (in 1870, 1871, 1873, and 1875). 

 The first idea was to dissolve the phosphate 

 of alumina in sulphuric acid, and to the 

 solution add potash salts, or, preferably, 

 ammonia vapour, to form an alum ; then 

 crystallise. The mother liquor was then 

 mixed with sawdust, and dried to a state fit 

 for manure. The second patent proposed to 

 refrigerate the mother liquor before mixing it 

 with sawdust to make it yield up more alum. 

 In the third patent, after the iron in the 

 mother liquor had been thrown down as 

 sulphide by ammoniacal gas water, and 

 phosphate of ammonia had been obtained, 



