PROGRESS OF CHEMISTRY IN SOUTH LANCASHIRE. 119 



In 1850-51, Mr. Spence made about 20 tons of alum per week. The 

 quantity now made by him amounts to 110 tons, of which 70 tons are pro- 

 duced in this district. Fully half of the total quantity manufactured in 

 England (300 tons per week) is made by his process. 



XIV. Protosulphate of Iron. ' 



This salt is manufactured in large quantities in this district, principally for 

 the use of dyers, the amount being about 80 tons per week. The process of 

 manufacture pursued here is as follows : — Iron pyrites, derived from the coal- 

 measures, and commonly called here coal brasses, is piled up in heaps, 

 watered and exposed to the atmosphere. A process of slow oxidation takes 

 place. Sulphate of iron with an excess of sulphuric acid is formed. The 

 latter is removed by means of scrap iron. The salt is obtained by evapora- 

 tion of the liquor, and is tolerably pure. An inferior quality is procured 

 from the mother-liquor, which contains alumina. 



XV. Compounds of Tin. 



Chlorides of Tiji. — The quantity of these compounds (estimated as crystal- 

 lized protochloride of tin) manufactured in this district amounts to about 

 I65 tons per week. 



Stannate of Soda. — This compound has for some time been extensively 

 used for the purpose of preparing calicoes which are intended to be printed 

 with so-called steam colours. It is usually obtained by fusing metallic tin 

 or finely powdered tin ore with nitrate of soda. It has been found that the 

 addition of 5 per cent, of arseniate of soda causes a saving in tin, by render- 

 ing, as it seems, the oxide of tin less soluble in the sulphuric acid, through 

 which the goods are subsequently passed. 



Stannate of soda is also prepared from scrap tin by Mr. Higgin's process. 

 Various attempts, with more or less success, have been made at various times 

 to separate the tin and the iron of scrap tin, or waste tinned iron, and so 

 utilize the former metal. Mr. Higgin acts on the scrap with a mixture of 

 muriatic acid and a little nitrate of soda. When muriatic acid is used 

 alone, the iron diissolves more rapidly than the tin, but when nitrate of soda 

 is added, the tin is acted on in preference. The whole of the nitrate of soda 

 disappears, and the resulting products are bichloride of tin, chloride of 

 ammonium, and chloride of sodium, in accordance with the following equa- 

 tion: 



4Sn+10ClH + NaNOe=4.SnCl,-fNH,Cl-fNaCl + 6HO. 

 The bichloride of tin is then converted, by the excess of tin present, into 

 protochloride. A little iron dissolves at the same time and is separated by 

 means of chalk, which precipitates the protoxide of tin, leaving the iron in 

 solution. The former is then converted, by fusion with nitrate of soda and 

 caustic soda, into stannate of soda, with evolution of ammonia. The iron 

 stripped of the tin is employed for the precipitation of copper. 



XVI. Copper Ores. 



Mr. William Henderson has introduced into this district a mode of dealing 

 with very weak copper ores, which has been found extremely successful at 

 Alderley, where the sandstone contains only \\ per cent, of copper, in the 

 form of carbonate and arseniate. The sand containing the copper is put 

 into wooden vats with muriatic acid, and fresh sand added until the amount 

 of copper is sufficient for saturation. The solution is then drawn off, and the 

 copper precipitated by waste or scrap iron. In this way ores otherwise use- 

 less have become valuable. 



